2009.06Design Criteria for Infrastrcture Projects-Rev 02 Final June

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Guidance Document Design Criteria for Infrastructure Projects

The Great Socialist People’s Libyan Arab Jamahiriya

Housing and Infrastructure Board (HIB)

Program Management Department (PMD)

Revision No. 2

June 2009

The Great Socialist People’s Libyan Arab Jamahiriya Housing and Infrastructure Board Program Management Department

Guidance Document Design Criteria for Infrastructure Projects

Revision No. 02 June 2009

JUNE 2009 REVISION NO. 02

Revision Tracking

Revision No.: Description Date

Revision No. 00 DRAFT Version 01‐July‐08

Revision No. 01 Working Copy 21‐Aug‐08

Revision No. 02 Working Copy June 2009

JUNE 2009 REVISION NO. 02 I

Table of ContentsACRONYMS AND ABBREVIATIONS ...................................................................................................... I

INTRODUCTION ................................................................................................................................. 1

1 WATER DESIGN STANDARDS ........................................................................................ 1-1

1.1 OBJECTIVES .............................................................................................................................. 1-1

1.1.1 OPERATION AND MAINTENANCE ASPECTS ........................................................................... 1-1

1.2 POTABLE WATER DEMAND .................................................................................................... 1-1

1.3 WATER TRANSPORT AND DISTRIBUTION SYSTEM ................................................................ 1-3

1.3.1 RESERVOIR DESIGN ................................................................................................................. 1-3

1.3.2 GROUND LEVEL TANKS ........................................................................................................... 1-4

1.3.3 ELEVATED WATER TANKS ....................................................................................................... 1-4

1.3.4 TRANSPORT WATER LINES...................................................................................................... 1-5

1.3.5 DISTRIBUTION WATER LINES .................................................................................................. 1-8

1.3.6 FIRE HYDRANTS ..................................................................................................................... 1-10

1.3.7 LATERALS ............................................................................................................................... 1-10

1.3.8 BACKFLOW PREVENTION ...................................................................................................... 1-11

1.3.9 OPERATION AND MAINTENANCE ........................................................................................ 1-11

1.4 WATER WELL DESIGN ........................................................................................................... 1-11

1.5 SURFACE WATER, GROUND WATER, AND SEAWATER TREATMENT ................................. 1-15

1.5.1 PURPOSE ................................................................................................................................ 1-15

1.5.2 WATER TREATMENT DESIGN CRITERIA ............................................................................... 1-17

2 SEWERAGE ................................................................................................................... 2-1

2.1 SEWER DESIGN CRITERIA ........................................................................................................ 2-1

2.1.1 SEWAGE FLOW ........................................................................................................................ 2-1

2.1.2 HYDRAULIC ANALYSES ............................................................................................................ 2-3

2.1.3 FLOW VELOCITIES.................................................................................................................... 2-4

2.1.4 DEPTH OF FLOW ...................................................................................................................... 2-4

2.1.5 PIPE GRADIENTS ...................................................................................................................... 2-5

2.1.6 PIPE MATERIALS ...................................................................................................................... 2-6

2.1.7 MINIMUM COVER REQUIREMENTS ....................................................................................... 2-6

2.1.8 UTILITY CROSSINGS ................................................................................................................. 2-6

2.1.9 MANHOLES .............................................................................................................................. 2-7

2.2 PUMPING STATIONS ............................................................................................................... 2-8

2.2.1 PUMPING STATION TYPE ........................................................................................................ 2-8

2.2.2 PUMP SELECTION .................................................................................................................. 2-10

JUNE 2009 REVISION NO. 02 II

2.2.3 PUMPING STATION STRUCTURES ........................................................................................ 2-11

2.2.4 SURGE PROTECTION ............................................................................................................. 2-11

2.2.5 ELECTRICAL AND INSTRUMENTATION SYSTEMS ................................................................ 2-11

2.2.6 ODOR CONTROL .................................................................................................................... 2-12

2.2.7 RISING MAINS ........................................................................................................................ 2-12

2.2.8 AIR VALVES AND WASHOUTS ............................................................................................... 2-12

2.2.9 EMERGENCY POWER SUPPLY ............................................................................................... 2-13

2.2.10 PUMPING STATIONS OPERATIONS AND MAINTENANCE ................................................... 2-13

3 SEWAGE TREATMENT .................................................................................................. 3-1

3.1 PURPOSE .................................................................................................................................. 3-1

3.2 SEWAGE TREATMENT DESIGN CRITERIA ............................................................................... 3-2

3.2.1 POPULATION AND GROWTH PROJECTIONS .......................................................................... 3-3

3.2.2 SEWAGE FLOW GENERATION................................................................................................. 3-3

3.2.3 SEWAGE LOADINGS ................................................................................................................ 3-4

3.2.4 DESIGN DISCHARGE QUALITY LIMITATIONS ......................................................................... 3-4

3.3 SITE SPECIFIC DESIGN CONSIDERATIONS .............................................................................. 3-5

3.4 TREATMENT PROCESS DESIGN CRITERIA .............................................................................. 3-6

3.4.1 LIQUID PROCESS ...................................................................................................................... 3-6

3.4.2 LIQUID PROCESS HYDRAULIC SYSTEMS ............................................................................... 3-10

3.4.3 BIOSOLIDS SYSTEMS ............................................................................................................. 3-11

3.4.4 PUMPS AND PIPING FOR TREATMENT PLANTS .................................................................. 3-12

3.4.5 MECHANICAL ODOR CONTROL SYSTEMS ............................................................................ 3-13

3.4.6 LAGOON TREATMENT SYSTEMS .......................................................................................... 3-14

3.4.7 TERTIARY TREATMENT FOR LAGOONS ................................................................................ 3-17

3.4.8 PACKAGE TREATMENT PLANT .............................................................................................. 3-18

3.4.9 MOBILE PACKAGE TREATMENT PLANT ............................................................................... 3-18

4 STORM WATER ............................................................................................................ 4-1

4.1 STORM WATER MANAGEMENT POLICY ................................................................................ 4-1

4.1.1 STORM WATER QUANTITY MANAGEMENT .......................................................................... 4-2

4.1.2 ENHANCING STORM WATER QUALITY .................................................................................. 4-2

4.2 STORM WATER DESIGN CRITERIA .......................................................................................... 4-3

4.2.1 DESIGN STORM........................................................................................................................ 4-3

4.2.2 RUNOFF COEFFICIENTS ........................................................................................................... 4-6

4.2.3 RUNOFF VOLUMES .................................................................................................................. 4-6

4.3 HYDRAULIC ANALYSES ............................................................................................................ 4-7

JUNE 2009 REVISION NO. 02 III

4.3.1 FLOW VELOCITIES.................................................................................................................... 4-7

4.3.2 CLEAR TIMES ............................................................................................................................ 4-8

4.3.3 DEPTH OF FLOW ...................................................................................................................... 4-8

4.4 PIPE MATERIALS ...................................................................................................................... 4-8

4.4.1 PIPE GRADIENTS ...................................................................................................................... 4-9

4.4.2 MINIMUM COVER REQUIREMENTS ..................................................................................... 4-10

4.4.3 MANHOLES ............................................................................................................................ 4-10

4.4.4 CONNECTION CHAMBERS..................................................................................................... 4-10

4.4.5 CATCH BASINS AND TRENCH DRAINS .................................................................................. 4-11

4.4.6 UTILITY CROSSINGS ............................................................................................................... 4-11

4.5 DETENTION PONDS (SEPARATE STORM DRAINAGE ONLY) ................................................ 4-11

4.5.1 POND INLET AND OUTLET STRUCTURES ............................................................................. 4-12

4.5.2 DISCHARGE CONTROL STRUCTURES .................................................................................... 4-12

4.5.3 POND DEPTH ......................................................................................................................... 4-12

4.5.4 DETENTION POND EMPTYING .............................................................................................. 4-13

4.5.5 DRY DETENTION PONDS ....................................................................................................... 4-13

4.5.6 WET DETENTION PONDS ...................................................................................................... 4-13

4.5.7 RETENTION PONDS ............................................................................................................... 4-14

4.5.8 BURIED DETENTION CHAMBERS .......................................................................................... 4-14

4.6 OIL-WATER SEPARATORS ..................................................................................................... 4-14

4.7 STORM WATER MANAGEMENT WITHIN AN AIRPORT ....................................................... 4-16

4.7.1 BIRD SCARE ............................................................................................................................ 4-16

4.8 GROUNDWATER DEWATERING ........................................................................................... 4-17

4.9 PUMPING STATIONS AND RISING MAINS ........................................................................... 4-17

4.9.1 PUMPING STATION TYPE ...................................................................................................... 4-17

4.9.2 WET WELL VOLUME .............................................................................................................. 4-18

4.9.3 WET WELL DEPTH.................................................................................................................. 4-18

4.9.4 PUMP SELECTION .................................................................................................................. 4-19

4.9.5 PUMPING STATION STRUCTURES ........................................................................................ 4-19

4.9.6 SURGE PROTECTION ............................................................................................................. 4-19

4.9.7 ELECTRICAL AND INSTRUMENTATION SYSTEMS ................................................................ 4-20

4.9.8 RISING MAINS ........................................................................................................................ 4-20

4.9.9 AIR VALVES AND WASHOUTS ............................................................................................... 4-20

4.9.10 EMERGENCY POWER SUPPLY ............................................................................................... 4-21

4.9.11 RELIABILITY ............................................................................................................................ 4-21

JUNE 2009 REVISION NO. 02 IV

5 WATER REUSE FOR LANDSCAPE IRRIGATION ............................................................... 5-1

5.1 GENERAL .................................................................................................................................. 5-1

5.1.1 IRRIGATION SUPPLY ................................................................................................................ 5-1

5.1.2 TRANSMISSION NETWORK ..................................................................................................... 5-1

5.1.3 DISTRIBUTION NETWORK ....................................................................................................... 5-2

5.1.4 IRRIGATION WATER QUALITY STANDARDS ........................................................................... 5-2

5.2 IRRIGATION DESIGN CRITERIA................................................................................................ 5-3

5.2.1 IRRIGATION DEMANDS ........................................................................................................... 5-3

5.2.2 DISTRIBUTION NETWORK ....................................................................................................... 5-4

5.2.3 FLOW METERS AND STRUCTURES ......................................................................................... 5-6

5.2.4 STORAGE .................................................................................................................................. 5-7

5.2.5 PUMPING STATIONS ............................................................................................................... 5-7

5.2.6 FIRE HYDRANTS ....................................................................................................................... 5-9

5.2.7 ELECTRICAL AND INSTRUMENTATION SYSTEMS .................................................................. 5-9

6 STANDARDS FOR BARRIER-FREE DESIGN ...................................................................... 6-1

6.1 INTRODUCTION ....................................................................................................................... 6-1

6.1.1 PURPOSE .................................................................................................................................. 6-1

6.1.2 APPLICATION ........................................................................................................................... 6-1

6.1.3 DEFINITION OF SIGNIFICANT RENOVATION .......................................................................... 6-1

6.1.4 MAINTENANCE ........................................................................................................................ 6-1

6.1.5 EMERGENCY EVACUATION PLANNING .................................................................................. 6-1

6.2 EXTERIOR AREAS ..................................................................................................................... 6-2

6.2.1 PARKING AND DROP-OFF AREAS ........................................................................................... 6-2

6.2.2 WALKWAYS AND RAMPS ........................................................................................................ 6-6

6.2.3 ENTRANCES AND EXITS ......................................................................................................... 6-10

6.2.4 EXTERIOR AMENITIES............................................................................................................ 6-13

6.3 INTERIOR AREAS .................................................................................................................... 6-13

6.3.1 STAIRS AND RAMPS .............................................................................................................. 6-13

6.3.2 LOBBIES AND CORRIDORS .................................................................................................... 6-15

6.3.3 ELEVATORS AND LIFTS .......................................................................................................... 6-15

6.3.4 INTERIOR DOORS AND DOORWAYS..................................................................................... 6-16

6.4 FACILITIES .............................................................................................................................. 6-18

6.4.1 WASHROOMS/BATHROOMS/TOILETS ................................................................................. 6-18

6.4.2 SHOWER AND BATH FACILITIES ........................................................................................... 6-20

6.4.3 DRINKING FOUNTAINS .......................................................................................................... 6-24

JUNE 2009 REVISION NO. 02 V

6.4.4 PUBLIC PAY TELEPHONES ..................................................................................................... 6-25

6.4.5 CONTROLS ............................................................................................................................. 6-25

6.4.6 SIGNAGE ................................................................................................................................ 6-26

6.4.7 TACTILE WARNINGS .............................................................................................................. 6-27

6.4.8 COUNTERS AND LINE UP GUIDES ......................................................................................... 6-29

6.4.9 PLACES OF ASSEMBLY ........................................................................................................... 6-29

6.4.10 ASSISTED LISTENING DEVICES .............................................................................................. 6-30

6.4.11 VISUAL AND AUDIBLE ALARMS ............................................................................................ 6-31

6.4.12 LIFE SAFETY ............................................................................................................................ 6-31

6.4.13 COOKING & LAUNDRY FACILITIES ........................................................................................ 6-31

7 SURVEYING STANDARDS .............................................................................................. 7-1

7.1 PURPOSE .................................................................................................................................. 7-1

7.2 HORIZONTAL CONTROL SURVEYS .......................................................................................... 7-1

7.2.1 DEFINITION .............................................................................................................................. 7-1

7.2.2 FIELD METHODS ...................................................................................................................... 7-1

7.2.3 COORDINATE ADJUSTMENT ................................................................................................... 7-2

7.3 VERTICAL CONTROL SURVEYS ................................................................................................ 7-2

7.3.1 DEFINITION .............................................................................................................................. 7-2

7.3.2 GPS NETWORK DESIGN EXAMPLE:......................................................................................... 7-3

7.3.3 BENCHMARKS .......................................................................................................................... 7-4

7.4 TOPOGRAPHIC SURVEYS ......................................................................................................... 7-5

7.4.1 DEFINITION .............................................................................................................................. 7-5

7.4.2 UTILITY SURVEYS ..................................................................................................................... 7-5

7.4.3 DIGITAL TERRAIN MODEL (DTM) ........................................................................................... 7-6

7.4.4 ROUTE SURVEY ........................................................................................................................ 7-6

7.4.5 CONSIDERATIONS - OTHER TECHNOLOGY ............................................................................ 7-7

7.4.6 WORK PRODUCT ..................................................................................................................... 7-7

7.4.7 INFORMATION REQUIRED ...................................................................................................... 7-7

7.4.8 MONUMENTS .......................................................................................................................... 7-8

7.4.9 FIELD PROCEDURES ................................................................................................................. 7-8

7.4.10 TOPOGRAPHIC FEATURES ..................................................................................................... 7-10

7.4.11 ELECTRONIC DATA ................................................................................................................ 7-10

7.4.12 DATA COLLECTION ................................................................................................................ 7-10

7.5 CONSTRUCTION STAKING ..................................................................................................... 7-11

7.5.1 FIELD METHODS .................................................................................................................... 7-11

JUNE 2009 REVISION NO. 02 VI

7.6 AS-BUILT SURVEYS ................................................................................................................ 7-11

7.6.1 DEFINITION ............................................................................................................................ 7-11

7.6.2 DELIVERABLE ......................................................................................................................... 7-11

7.7 SURVEY MAP CHECK LIST ...................................................................................................... 7-11

ATTACHMENT 7-A ................................................................................................................................. 7-13

8 ROADWAY ................................................................................................................... 8-1

8.1 HIGHWAY SYSTEMS ................................................................................................................ 8-1

8.1.1 FUNCTIONAL CLASSIFICATION ............................................................................................... 8-1

8.1.2 FREEWAYS................................................................................................................................ 8-1

8.1.3 EXPRESSWAYS ......................................................................................................................... 8-1

8.1.4 ARTERIALS ................................................................................................................................ 8-2

8.1.5 COLLECTORS ............................................................................................................................ 8-2

8.1.6 LOCAL ROADS .......................................................................................................................... 8-2

8.2 TRAFFIC .................................................................................................................................... 8-2

8.2.1 LEVEL OF SERVICE ................................................................................................................... 8-2

8.2.2 DESIGN VEHICLES .................................................................................................................... 8-3

8.3 SPEED ....................................................................................................................................... 8-4

8.3.1 DESIGN SPEED ......................................................................................................................... 8-4

8.3.2 POSTED SPEED ......................................................................................................................... 8-5

8.3.3 RAMPS...................................................................................................................................... 8-5

8.4 SIGHT DISTANCE ...................................................................................................................... 8-6

8.4.1 STOPPING SIGHT DISTANCE (SSD) .......................................................................................... 8-6

8.4.2 PASSING SIGHT DISTANCE (PSD) ............................................................................................ 8-8

8.4.3 DECISION SIGHT DISTANCE..................................................................................................... 8-8

8.5 HORIZONTAL ALIGNMENT ...................................................................................................... 8-9

8.5.1 GENERAL .................................................................................................................................. 8-9

8.5.2 TYPES OF HORIZONTAL CURVATURE ................................................................................... 8-10

8.5.3 MINIMUM CURVATURE ........................................................................................................ 8-14

8.5.4 SPIRAL CURVE TRANSITION .................................................................................................. 8-15

8.5.5 HORIZONTAL STOPPING SIGHT DISTANCE .......................................................................... 8-17

8.5.6 SUPERELEVATION .................................................................................................................. 8-18

8.5.7 MINIMUM LANE WIDTH ON CURVES .................................................................................. 8-23

8.6 VERTICAL ALIGNMENT .......................................................................................................... 8-24

8.6.1 GRADES .................................................................................................................................. 8-24

8.6.2 VERTICAL CURVES ................................................................................................................. 8-26

JUNE 2009 REVISION NO. 02 VII

8.6.3 COMBINING HORIZONTAL AND VERTICAL ALIGNMENTS .................................................. 8-30

8.6.4 VERTICAL CLEARANCES ......................................................................................................... 8-33

8.7 CROSS SECTION ELEMENTS .................................................................................................. 8-34

8.7.1 GENERAL ................................................................................................................................ 8-34

8.7.2 TRAVEL LANES ....................................................................................................................... 8-34

8.7.3 SHOULDERS ........................................................................................................................... 8-35

8.7.4 CURBING ................................................................................................................................ 8-36

8.7.5 BORDERS, BUFFER STRIPS AND SIDEWALKS ....................................................................... 8-36

8.7.6 MEDIANS ................................................................................................................................ 8-36

8.7.7 CROSS SLOPES ....................................................................................................................... 8-38

8.7.8 SIDE SLOPES ........................................................................................................................... 8-38

8.7.9 DITCH SECTIONS .................................................................................................................... 8-38

8.7.10 RIGHT-OF-WAY LIMITS .......................................................................................................... 8-39

8.7.11 HORIZONTAL CLEARANCES ................................................................................................... 8-40

8.7.12 OTHERS .................................................................................................................................. 8-41

8.8 GRADE SEPARATIONS AND INTERCHANGES ....................................................................... 8-43

8.8.1 WARRANTS ............................................................................................................................ 8-43

8.8.2 INTERCHANGE TYPES ............................................................................................................ 8-44

8.8.3 INTERCHANGE ANALYSIS ...................................................................................................... 8-49

8.8.4 TRAFFIC LANE PRINCIPLES .................................................................................................... 8-50

8.8.5 LANE BALANCE ...................................................................................................................... 8-51

8.8.6 FREEWAY/RAMP JUNCTIONS ............................................................................................... 8-54

8.8.7 CAPACITY AND LEVEL OF SERVICE ....................................................................................... 8-69

8.8.8 RAMP DESIGN ........................................................................................................................ 8-72

8.8.9 SPACING OF RAMP TERMINALS ........................................................................................... 8-75

8.8.10 APPENDICES ........................................................................................................................... 8-77

8.9 SUMMARY OF DESIGN PARAMETERS .................................................................................. 8-90

8.9.1 LOCAL ROADS AND STREETS ................................................................................................ 8-90

8.9.2 COLLECTORS .......................................................................................................................... 8-95

8.9.3 ARTERIALS ............................................................................................................................ 8-101

8.9.4 FREEWAYS/EXPRESSWAYS ................................................................................................. 8-108

8.10 HIGHWAY FACILITIES .......................................................................................................... 8-114

8.10.1 GENERAL .............................................................................................................................. 8-114

8.10.2 PUBLIC TRANSPORT FACILITIES .......................................................................................... 8-115

8.10.3 PARKING FACILITIES ............................................................................................................ 8-117

JUNE 2009 REVISION NO. 02 VIII

8.10.4 SAFETY BARRIERS ................................................................................................................ 8-122

8.10.5 IMPACT ATTENUATOR SYSTEMS ........................................................................................ 8-128

8.10.6 TRAFFIC CALMING ............................................................................................................... 8-130

8.11 INTERSECTIONS ................................................................................................................... 8-134

8.11.1 GENERAL DESIGN CONSIDERATIONS ................................................................................. 8-134

8.11.2 INTERSECTION SIGHT DISTANCE ........................................................................................ 8-140

8.11.3 INTERSECTION TURNS......................................................................................................... 8-149

8.12 ROUNDABOUTS ................................................................................................................... 8-181

8.12.1 GENERAL .............................................................................................................................. 8-181

8.12.2 DESIGN PRINCIPLES ............................................................................................................. 8-181

8.12.3 GENERAL FEATURES OF A ROUNDABOUT ......................................................................... 8-182

8.12.4 SPEEDS THROUGH THE ROUNDABOUT ............................................................................. 8-184

8.12.5 DESIGN VEHICLE .................................................................................................................. 8-189

8.12.6 INSCRIBED CIRCLE DIAMETER ............................................................................................ 8-189

8.12.7 CIRCULATING ROADWAY WIDTH ....................................................................................... 8-190

8.12.8 ENTRY WIDTH ...................................................................................................................... 8-191

8.12.9 ENTRY CURVES .................................................................................................................... 8-193

8.12.10 EXIT CURVES ....................................................................................................... 8-195

8.12.11 VERTICAL CONSIDERATIONS ............................................................................. 8-197

8.12.12 VISIBILITY ............................................................................................................ 8-200

8.12.13 ENTRY CURBING ................................................................................................. 8-203

8.12.14 SAFETY AT ROUNDABOUTS ............................................................................... 8-204

9 FLEXIBLE PAVEMENT DESIGN MANUAL ........................................................................ 9-1

9.1 PURPOSE .................................................................................................................................. 9-1

9.2 GENERAL .................................................................................................................................. 9-1

9.3 REFERENCES ............................................................................................................................ 9-1

9.4 DESIGN CONSIDERATIONS ...................................................................................................... 9-1

9.5 PAVEMENT TYPES ................................................................................................................... 9-2

9.6 DEFINITIONS AND ABBREVIATIONS ....................................................................................... 9-2

9.7 PAVEMENT DESIGN PROCESS................................................................................................. 9-3

9.7.1 COLLECT BASIC PROJECT DATA .............................................................................................. 9-3

9.7.2 DETERMINE THE PRELIMINARY SCOPE OF WORK ................................................................ 9-4

9.7.3 FRICTION .................................................................................................................................. 9-4

9.7.4 WIDENING AND CORRECTIVE WORK TO THE EXISTING PAVEMENT ................................... 9-5

9.7.5 DETERMINE DBR...................................................................................................................... 9-5

JUNE 2009 REVISION NO. 02 IX

9.7.6 SUBMIT ALL PAVEMENT DESIGN INFORMATION ................................................................. 9-5

9.7.7 HIB REVIEWS SCOPE OF WORK .............................................................................................. 9-5

9.7.8 HIB REVIEWS DBR DETERMINATION ..................................................................................... 9-5

9.7.9 REQUEST LAB ANALYSIS FROM MATERIALS LAB .................................................................. 9-9

9.7.10 USE DBR FROM PREVIOUS WORK .......................................................................................... 9-9

9.7.11 REVIEW AND ANALYSIS OF THE DATA SUBMITTED .............................................................. 9-9

9.7.12 DESIGN ENGINEER CONDUCTS PAVEMENT DESIGN ANALYSIS ........................................... 9-9

9.7.13 NEW/RECONSTRUCTED PAVEMENT ...................................................................................... 9-9

9.7.14 PAVEMENT OVERLAYS ............................................................................................................ 9-9

9.7.15 COMBINATION (PAVEMENT OVERLAY WITH WIDENING) ................................................... 9-9

9.7.16 SUBMIT PAVEMENT DESIGN RECOMMENDATION TO HIB ENGINEER ................................ 9-9

9.7.17 REVIEWS AND APPROVES ..................................................................................................... 9-10

9.8 NEW AND RECONSTRUCTED PAVEMENT ............................................................................ 9-10

9.9 PAVEMENT OVERLAYS .......................................................................................................... 9-25

9.10 RECYCLING ............................................................................................................................. 9-39

9.11 SKID RESISTANCE ................................................................................................................... 9-40

9.12 REFERENCES .......................................................................................................................... 9-41

10 UNIFORM TRAFFIC CONTROL DEVICES ....................................................................... 10-1

10.1 TRAFFIC CONTROL FOR WORK AREA (SUPPLEMENTS) ...................................................... 10-1

10.2 ROADWAY CONSTRUCTION ................................................................................................. 10-1

10.2.1 CORRIDOR AND NETWORK-WIDE CONSTRUCTIONS .......................................................... 10-1

10.2.2 AUTHORITY ............................................................................................................................ 10-2

10.3 TRAFFIC CONTROL ZONES .................................................................................................... 10-5

10.3.1 APPLICATION ......................................................................................................................... 10-6

10.3.2 GUIDELINE ............................................................................................................................. 10-6

10.3.3 TRAFFIC MANAGEMENT PLANS ........................................................................................... 10-8

10.3.4 COMPONENTS OF TEMPORARY TRAFFIC CONTROL ZONES............................................... 10-9

11 LANDSCAPE DESIGN CRITERIA .................................................................................... 11-1

11.1 LANDSCAPE DESIGN CRITERIA .............................................................................................. 11-1

11.1.1 LANDSCAPE AND PLANTING ................................................................................................. 11-1

11.1.2 PLANTING ON PRIVATE DEVELOPMENT PARCELS .............................................................. 11-3

11.1.3 PLANTING ON PUBLIC STREETS AND STREETS WITHIN PRIVATE DEVELOPMENTS .......... 11-5

11.1.4 PLANTING ON PUBLIC PARKS AND LANDSCAPED OPEN AREAS ........................................ 11-6

11.2 LANDSCAPING PLANS SUBMITTALS REQUIREMENTS ......................................................... 11-7

11.3 LANDSCAPE GRADING PLAN................................................................................................. 11-8

JUNE 2009 REVISION NO. 02 X

11.3.1 TREE AND PLANT MAINTENANCE ...................................................................................... 11-11

12 STREETSCAPE ............................................................................................................. 12-1

12.1 INTRODUCTION ..................................................................................................................... 12-1

12.2 GOOD DESIGN ....................................................................................................................... 12-1

12.3 OVERARCHING OBJECTIVE.................................................................................................... 12-2

12.4 PRINCIPLES............................................................................................................................. 12-2

12.5 DESIGN GUIDELINES AND CRITERIA ..................................................................................... 12-4

12.5.1 PLANTING REGIMES .............................................................................................................. 12-4

12.5.2 FOOTWAY LAYOUT ................................................................................................................ 12-5

12.5.3 PAVING................................................................................................................................... 12-5

12.5.4 STREET FURNITURE AND FEATURES .................................................................................... 12-7

12.5.5 LIGHTING ............................................................................................................................... 12-7

12.5.6 BENCHES ................................................................................................................................ 12-8

12.5.7 PLANTERS ............................................................................................................................... 12-8

12.5.8 PLAYGROUND EQUIPMENT .................................................................................................. 12-8

12.5.9 WATER FEATURES IN PUBLIC OPEN SPACES ....................................................................... 12-9

12.5.10 SHADING STRATEGIES .......................................................................................... 12-9

12.5.11 SIGNAGE ............................................................................................................... 12-9

12.6 DELIVERING THE PRINCIPLES ................................................................................................ 12-9

13 BRIDGE INSPECTION................................................................................................... 13-1

13.1 INTRODUCTION ..................................................................................................................... 13-1

13.1.1 REFERENCES .......................................................................................................................... 13-1

13.1.2 AASHTO INSPECTION MANUALS .......................................................................................... 13-2

13.1.3 INSPECTION PROCEDURES ................................................................................................... 13-8

13.2 QUALIFICATIONS, RESPONSIBILITIES, AND DUTIES OF BRIDGE INSPECTION PERSONNEL13-9

13.2.1 REQUIREMENTS..................................................................................................................... 13-9

13.2.2 BRIDGE INSPECTION PERSONNEL ...................................................................................... 13-10

13.2.3 BRIDGE INSPECTIONS BY CONTRACTORS .......................................................................... 13-11

13.2.4 USE OF THE CONTRACTOR POOL ....................................................................................... 13-12

13.3 FIELD INSPECTION REQUIREMENTS ................................................................................... 13-13

13.3.1 TYPES OF BRIDGE INSPECTION ........................................................................................... 13-13

13.3.2 INITIAL INSPECTIONS .......................................................................................................... 13-14

13.3.3 ROUTINE INSPECTIONS ....................................................................................................... 13-14

13.3.4 DAMAGE INSPECTIONS ....................................................................................................... 13-15

13.3.5 IN-DEPTH INSPECTIONS ...................................................................................................... 13-15

JUNE 2009 REVISION NO. 02 XI

13.3.6 SPECIAL INSPECTIONS ......................................................................................................... 13-24

13.4 RATINGS AND LOAD POSTING ............................................................................................ 13-24

13.4.1 OVERVIEW ........................................................................................................................... 13-24

13.4.2 CONDITION RATINGS .......................................................................................................... 13-25

13.4.3 APPRAISAL RATINGS ........................................................................................................... 13-27

13.4.4 LOAD RATINGS .................................................................................................................... 13-31

13.4.5 LEGAL LOADS AND LOAD POSTING .................................................................................... 13-37

13.5 ROUTING AND PERMITS ..................................................................................................... 13-43

13.5.1 OVERVIEW ........................................................................................................................... 13-43

13.5.2 ROLE OF INSPECTION ENGINEERS AND THE TRAFFIC AUTHORITIES .............................. 13-44

13.5.3 PERMITS ............................................................................................................................... 13-44

13.5.4 EXAMPLE OF INVENTORY, OPERATING, AND PERMIT LOADS ......................................... 13-47

13.6 BRIDGE PROGRAMMING .................................................................................................... 13-51

13.6.1 BASIS FOR BRIDGE REHABILITATION OR REPLACEMENT ................................................. 13-51

13.6.2 BRIDGE PROGRAM .............................................................................................................. 13-51

13.6.3 SUFFICIENCY RATINGS ........................................................................................................ 13-53

13.7 BRIDGE RECORDS ................................................................................................................ 13-57

13.7.1 OVERVIEW ........................................................................................................................... 13-57

13.7.2 DEFINITION OF TERMS ........................................................................................................ 13-58

13.7.3 CONTRACTOR REQUIREMENTS .......................................................................................... 13-60

13.7.4 CODING GUIDELINES ........................................................................................................... 13-61

13.7.5 FORMS ................................................................................................................................. 13-62

13.7.6 CALCULATIONS .................................................................................................................... 13-65

13.7.7 DATA SUBMITTAL ................................................................................................................ 13-69

13.7.8 THE BRIDGE FOLDER ........................................................................................................... 13-73

13.8 APPENDIX ............................................................................................................................. 13-75

14 ELECTRICAL ................................................................................................................ 14-1

15 TELECOMMUNICATION .............................................................................................. 15-1

16 GAS DISTRIBUTION .................................................................................................... 16-1

JUNE 2009 REVISION NO. 02 1

Acronyms and Abbreviations 2WLTL Two‐Way Left‐Turn Lane ADT Average Daily Traffic ANSI American National Standards Institute AOR Actual Oxygenation Rate AWWA American Water Works Association CBD Central Business District C‐D Collector‐Distributor CIE The International Commission on Illumination cm Centimeters Cs carbon steel CT Contact Time D nominal pipe Diameter d Depth DHV Design Hourly Volume DIP Ductile Iron Pipe EWT Elevated Water Tank FAA Federal Aviation Administration FRP Fiberglass Reinforced Plastic Fs side friction factor GECOL General Electric Company of Libya GLT Ground Level Tanks GMR Great Man‐made River GRP Glass Fiber Reinforced Plastic GWA General Water Authority H Height HDPE High Density Polyethylene HI Hydraulic Institute HIB Housing and Infrastructure Board ICD Inscribed Circle Diameter l/d/c liters per day per capita km/h kilometers per hour M Meters m3 cubic meters MCL Maximum Contaminant Level mg/l milligrams per liter Ml Milliliters MLSS Mix Liquor Suspended Solids Mm Millimeters MPN Most Probable Number NPSHR Net Positive Suction Head Required NTU Nephelometric Turbidity Unit pc/h passenger cars per hour PCC Point of Compound Curvature PF Peaking Factor PRD Perception/Reaction Distance PSC Point of Spiral to Curve

JUNE 2009 REVISION NO. 02 2

PSD Passing Sight Distance PT Point of Tangency PVC Polyvinyl Chloride Q Flow RCP Reinforced Concrete Pipe ROW Right‐Of‐Way rpm revolutions per minute RSR Rapid Sludge Return SCADA Supervisory Control And Data Acquisition SOR Standard Oxygenation Rate SSD Stopping Sight Distance TDS Total Dissolved Solids TSE Treated Sewage Effluent UI Longitudinal Uniformity Ratio uPVC Unplasticised Polyvinyl Chloride USEPA United States Environmental Protection Agency VCP Vitrified Clay Pipe WEF Water Environment Federation WSP Welded Steel Pipe

JUNE 2009 REVISION NO. 02 INTRODUCTION 1

Introduction

This Design Criteria for Infrastructure presents design criteria for water, sewage, storm water, barrier‐free, surveying, roadways, pavement design, uniform traffic control devices, landscape, bridge inspection, electrical, telecommunication and gas systems. The criteria presented in the following sections are provided as the basis for all designs prepared for the Libya Housing and Infrastructure Board (HIB).

This design criteria is presented to support the design intent of the HIB infrastructure planning.

Plans and construction documents for all systems shall be submitted to HIB for review and approval at designated stages of the project. Designs shall be in accordance with the following guidelines and with all other applicable criteria and shall be carried out using approved modeling software as noted in each section. If deviations are required for special cases, HIB approval shall be obtained on a case by case basis.

These design criteria should be implemented in conjunction with the Housing and Infrastructure Master Specifications and Standard Details and the Design Criteria for Housing Projects. The geotechnical design criteria for treatment plants and pump stations shall be in accordance with the Section 5.6 of the Design Criteria for Housing Projects.

JUNE 2009 REVISION NO. 02 WATER Design Standards 1‐1

1 Water Design Standards

1.1 Objectives The objective of the Libya Housing and Infrastructure Board (HIB) water supply system is to provide safe, potable, adequate, reliable, efficient, and effective water supply facilities. Water service is to be provided in an economically and environmentally sustainable manner in terms of both water treatment and water distribution. The objective of the water treatment is to produce and maintain finished water quality that is hygienically safe and aesthetically pleasing, in an economic manner while complying with water quality standards provided by the World Health Organization (WHO) and/or the United States Environmental Protection Agency (USEPA). The evaluation of water quality should not be limited to the treatment facilities, but should extend the distribution system to the point of consumer consumption. The distribution system should maintain adequate pressure and safe water quality, while meeting fire protection needs.

Specific goals of the HIB are:

1. Provide water sources, water treatment plants, water storage facilities, and transmission and distribution delivery systems with sufficient capacity to supply current and future water demands;

2. Provide adequate and reliable water distribution facilities (supply mains, pump stations, service reservoirs, transmission, and distribution systems) that meet peak hour demands and sustained periods of high demand while maintaining adequate delivery pressures and water quality.

3. Provide a level of fire fighting capability adequate in relation to the recommendations defined in this document;

4. Maintain a safe, potable, adequate, and reliable water supply for consumers.

The water system design must be compatible with the overall community master development plan. The system layout shall be designed for, and take into account, water quality, pressure, flow rate, and long‐term planning. Hydraulic calculations performed by the designer shall be submitted to HIB for review and approval in support of the design.

1.1.1 Operation and Maintenance Aspects Water supply systems should be designed with consideration of the system’s current and future operation and maintenance requirements. The result will be a system that can be easily and economically operated and maintained using standard techniques and equipment essential for the reliability of the water system.

1.2 Potable Water Demand Water demand determination is the starting point for the design of water supply systems. Water demand is typically based on population data and population growth projections, combined with established values of the water demand per capita along with the specific needs of large water users. The water demand per capita is usually based on historical data and is typically dependent on the size of


the community. Smaller community water use is predominantly residential, while larger community water use can include significant requirements for commercial and industrial water demand. For smaller communities with significant commercial or industrial components, special consideration should be given to the commercial and industrial water needs.

Other factors in water demand calculations for facilities design are the seasonal and daily variations in demand with particular emphasis on maximum daily demand, maximum hourly demand, and fire fighting demand.

Table 1—1 presents the demand criteria and key factors for use in sizing the water supply, treatment, and distribution systems. Water systems are typically designed to serve both the current and the projected population for 20 to 25 years in the future. To limit the immediate capital costs, designs are usually prepared for phased implementation, with system upgrades added as the demand increases over time.

Table 1—1: Criteria for Establishing Water Demand

Component Design Criteria

Average water demand m3/d

[Qave]

(Water distribution pipe leakage, pipe flushing, lawn irrigation etc. included.)

Average Water Demand

Population [inhabitants] Demand [Q]

<3,000 Q= 150 l/d/c

3,000 – 20,000 Q= 180 l/d/c

20,000 – 50,000 Q= 200 l/d/c

50,000 – 100,000 Q= 250 l/d/c

100,000 – 500,000 Q=300 l/d/c

>500,000 Q=350 l/d/c

Maximum daily demand m3/d

[Qmaxd=kmaxd *Qave]

Maximum Daily Demand Factor

Population [inhabitants] Factor kmaxd [‐]

<10,000 1.8

10,000 – 30,000 1.5

30,000 – 100,000 1.4

> 100,000 1.3



Maximum Peak hour demand m3/h

[Qhmax=khmax* Qave]

Maximum Hour Demand Factor

Population [inhabitants] Factor khmax [‐]

<10,000 3.0

10,000 –30,000 2.7

30,000 – 100,000 2.5

> 100,000 2.0

Fire fighting demand Qff [l/s]

Using any suitable fire fighting equation (i.e. AWWA M31 Distribution System Requirements for Fire Fighting) with a total duration of 4 hours (assume two fires at the same time with 2 hour duration each).

Population [inhabitants] Qff, Fire Demand (l/s)

Up to 10,000 20

10,000 – 25,000 25

25,000 – 50,000 30

50,000 – 100,000 40

100,000 – 200,000 45

greater than 200,000 50

Minimum demand [Qdmin] [Qhmin]

Qdmin = 0.6 to 0. 7 *Qave

Qhmin = 0.3*Qave

1.3 Water Transport and Distribution System

1.3.1 Reservoir Design This section addresses reservoir sizing of Ground Level Tanks (GLT) and Elevated Water Tanks (EWT). Values from the water demand projections, as previously addressed, shall be used to calculate the design capacity of the GLT and EWT.


1.3.2 Ground Level Tanks Ground Level Tanks shall be designed to handle storage volume for the maximum day demand. The volume shall be calculated using the differences between the cumulative curves of constant pumping and hourly consumption during a maximum day. Fire fighting volume shall also be added to this calculated amount and calculated volumes shall be based on the following equation:

V = (Qmaxd – Qp) + 80% of fire fight demand (assume two fires for 2 hours duration each)

Where:

V is the Volume (m3)

Qmaxd is the maximum daily demand (m3/d)

Qp is the constant water supply pumping rate (m3/d)

When GLT is filled from a water treatment plant, Qp would be the average treatment capacity of the plant. When the GLT is filled from groundwater wells, Qp would be the well output with the largest well out of service. When the supply of water to fill the tank is intermittent, then Qp should be considered to be zero. Tanks filled directly from the distribution system, either from a different pressure zone or via a pressure reduction valve should consider Qp to be zero. These types of tanks should be filled in four hours or less during the early morning hours when other demand are low.

The minimum storage capacity for systems not providing fire protection shall be equal to the average daily consumption. This requirement may be reduced when the source and treatment facilities have sufficient capacity with standby power to supplement peak demands of the system. Ground level storage tanks are generally used for storage only and not for setting hydraulic gradients in the system. These types of tanks serve as wet wells for booster pumps that serve the customers in a service area. If an existing reservoir is in good condition and able to handle the proposed design storage requirements, a new reservoir shall not be required. In addition, the residence time and internal mixing in tanks must be considered to avoid dead zones where stagnation may occur and to provide a sufficient turnover rate of the tank’s contents. In general, the tank’s contents should be replenished at least once every 3 days. Where possible, separate inlet and outlet pipes should be provided for all tanks.

1.3.3 Elevated Water Tanks EWT shall be designed to provide storage for 35% of maximum day demand. The volume shall be calculated using the differences between the cumulative curves of constant pumping and hourly consumption during a maximum day. Fire fighting volume shall also be added to this calculated amount. The greater of the two calculated volumes shall be used based on the following equations:

V = (Qmaxh – Qmaxd) + 20% of fire fight demand (for 4 hours) or

V = (Qmaxh – Qp) + 20% of fire fight demand (for 4 hours)

Where:

V is the Volume (m3)

Qmaxd is the maximum daily demand (m3/h)


Qmaxh is the maximum hourly demand (m3/h)

Qp is the constant water supply pumping rate (m3/h)

Elevated water tanks shall be designed similar to ground storage tanks and are intended to minimize the unusable storage below the minimum acceptable level. The height (h) of the EWT shall be designed to meet the water distribution system pressure requirements, as determined by the hydraulic modeling of the system. In absence of modeling, the following criteria may be used. The minimum level in the tank is based on providing a minimum pressure in the distribution system in accordance with the following:

• Normal demands based on providing a minimum pressure equal to 25 m at the highest ground elevation within the service area of the tank

• Fire fighting demands based on providing a minimum pressure equal to 15 m at the highest ground elevation within the service area of the tank

Volumes in the tank below the minimum level for firefighting are considered emergency reserves and may require temporary pumping to be delivered. In cases where sufficiently high ground levels are available, a ground storage tank may be used. In general, elevated tanks may be used in conjunction with supply pumps that can provide more than 65 percent of the demand in the tank’s service area.

1.3.4 Transport Water Lines Transport water lines are intended to deliver water from the main supply source to storage reservoirs and distribution networks. These lines are not intended to distribute water directly to service connections. Delivery pressures shall be maintained by pressure sustaining valves at ground reservoirs and by the hydrostatic head at elevated water tanks.

Network Analyses

Network analyses of the water system shall be performed to ensure that an adequate and safe water supply is available to all consumers connected to the system for all defined modes of operation. The system shall be sized in accordance with the design parameters listed in Table 1—2.

Table 1—2. Transport Water Line Design Parameters

TRANSPORT WATER LINES

Design Flow Qdes (average flow)

Use the greater of the following values: Qdes = Qave, v = 1.0 m/s, or Qdes = Qmaxd, v = 2.5 m/s

Minimum Pressure 5 m (0.5 bar) above the highest point in system (provided there are no

customers serviced by this line)

Maximum Operating Pressure

100 m (10 bar)


TRANSPORT WATER LINES

Design Maximum Pressure

Maximum Expected Operating pressure x 2 + water hammer allowance of 70 m (7 bar)

Minimum Velocity 0.6 m/s

Maximum Velocity 2.5 m/s

Materials1 Ø 150 mm ‐ 400 mm: PVC or HDPE Ø >400 mm: DIP, FRP or HDPE

Roughness Coefficient Per pipe specifications and formulas. Not to exceed a Hazen‐Williams

roughness coefficient of 140

1Consideration must be taken for aggressive soil conditions and economical comparison.

Fittings

The following fittings shall be included along the water transport lines for facilitating the operation, control, and maintenance:

1. Air release, Air/Vacuum, Combination Air and Vacuum relief Valves: Air release and vacuum relief valves are often needed along transmission mains. Air release valves shall be provided at summits along the pipe profile and along long stretches with uniform slope to purge out accumulated air in the pipe system. Air must be bled slowly from high points to prevent (1) “air binding” and (2) the reduction of the cross section of the pipe at high points. Combination air release valves are used to vent large quantities of air from the pipeline when the pipe in being filled as well as releasing the small quantities of accumulated air during normal operations. Air/vacuum valves are used to prevent excessively low pressures when the pump head drops quickly (as in power failures) to prevent column separation and at extreme high points in pipelines to prevent potential pipeline collapse due to vacuum. Vacuum relief valves can be as large as one‐sixth of the diameter of the transmission main, whereas air release valves may be as small as one‐fiftieth of the diameter of the pipe. The selection of the sizes of these valves shall be in accordance with AWWA’s Manual of Water Supply Practice M51 Air‐Release, Air/Vacuum & Combination Air Valves.

2. A combination of air and vacuum valves shall be provided at appropriate locations for quick air entry or vent to prevent cavitations and facilitate quick filling of the pipe. In general, air‐valves are to be installed at crest points, change in elevations and in case of constant rising mains having moderate slope, at a maximum spacing of 500 m to 750 m.

3. Washout valves: These valves will be provided at low points or sags along the pipe profile. These valves facilitate flushing, repair or maintenance of the pipe wherever necessary. In cases where the static head on these valves exceeds 15m, proper energy dissipation devices and erosion control shall be provided.


4. Isolating valves: The location of these valves shall consider the profile of the pipeline and the location of washout and air valves. Isolating valves shall be provided at a maximum distance of every 2 to 3 kilometers.

5. Isolating Valves with diameter smaller than 300 mm shall be gate valves and larger diameter shall be butterfly valves.

6. Non‐Return Valves (Check Valves): These valves will be provided in the pump station to prevent a reverse flow into the pumps and shall be of noiseless non‐slam type.

7. Tapping Sleeves and tees: These fittings are used to add branches for the pipe line. In general, tapping sleeves shall not be used where the branch size is greater than or equal to one half of the main pipe diameter. In such cases, standard tees should be used.

The pressure ratings of all fittings shall equal or exceed the maximum design pressure requirement for the pipeline.

All transport line valves not located in a pump station structure shall be installed inside reinforced concrete valve chambers.

Suction Pipes

Suction pipe diameters shall be sized with due regard for the pumping net positive suction head requirement (NPSHR), and shall generally provide for a flow velocity, v ≤ 10.0 m/s.

Pumps

Pump capacity shall be designed to meet the required water demand, Q, and total dynamic head, H. Elevated water tanks provide a buffer for constant speed pumps. For distribution systems without an elevated water tank, a variable running speed drive is required to allow the pumping rate to maintain a constant discharge pressure as the system demands are provided.

The following fittings shall be provided with each pump:

1. Isolation valves (one provided upstream and downstream of each pump to protect pumps and all associated fittings)

2. Non‐return valve or a hydraulically actuated control valve design to close more slowly than a non‐return valve. If a hydraulically actuated control valve is used, a special hydraulic transient analysis must be performed to demonstrate that excessive surge pressures will be controlled. These valve shall be placed directly downstream of the pumps

3. Flow meter (downstream of pump)

4. Pressure gage (downstream of pump)

5. Sampling tap (downstream of pump)


6. Air valve on discharge pressure main (downstream of pump)

Emergency Power Supply

All pumping stations shall be provided with back‐up, diesel engine‐driven electrical power generators sized to power 100 percent of the rated pumping station power demand.

Reliability

For reliability, provide installed spares for all rotating equipment shall be provided to provide N+1reliability (duplicate of largest pump). All equipment shall be supplied with the manufacturer’s required spare parts.

1.3.5 Distribution Water Lines Distribution water lines shall provide service to commercial and residential developments. Distribution lines, sized according to calculated demand, are divided into three categories: Main Lines, Secondary Lines, and Laterals.

Distribution Lines Network Analyses

Network analyses of the water system shall be performed to ensure that an adequate and safe water supply is available to all consumers connected to the system for all defined modes of operation. The system shall be in designed in accordance with the hydraulic design parameters listed in Table 1—3.

Table 1—3. Distribution Water Line Design Parameters

DISTRIBUTION WATER LINES

Secondary Line Main Line

Line Diameter Size < 200 mm > 200 mm

(All water lines used for firefighting shall be at least 200 mm)

Design Flow Qdes (average flow)

Use the greater of the following values: Qdes = Qave x Khmax Qdes = Qmaxd+ Qff

Minimum Pressure Head 15 m(1.5 bar)

Maximum Pressure Head 60 m (6.0 bar)

Minimum Design Velocity 0.1 m/s 0.6 m/s

Maximum Design Velocity 1.5 m/s 2.5 m/s

Materials1 PVC, HDPE Ø 150 mm ‐ 400 mm: PVC, HDPE

Ø > 400 mm: Ductile Iron

Gradient Not less than 0.1%


DISTRIBUTION WATER LINES

Secondary Line Main Line

Roughness Coefficient Per pipe specifications and formulas

1 Consideration must be taken for aggressive soil conditions and economical comparison.

Alignment

For distribution systems downstream of reservoirs, a ‘looped’ rather than ‘branched’ layout should be used to provide more than one supply route on distribution systems wherever possible. The valve arrangement shall be designed to limit the area needing to be shut down when isolating and repairing any section of water line is necessary.

Deviation of a pipeline around an obstruction can be achieved by deflection at pipe joints or in combination with bends or connectors. The deflection angle permitted at a flexible joint shall be in accordance with the pipe manufacturer’s recommendation. For laying plastic pipes on curves, minimum radii are to be as per pipe manufacturer’s recommendations. If deflection of joints does not provide the necessary deviation, bends and other fittings shall be used.

Pipe Cover and Placement

The pipe cover depth must follow the pipe manufacturer’s recommendations and protection requirements or meet the following criteria (whichever is greater):

Pipe Under Traffic: Cover Depth ≥ 1.0 m (Pipe thickness design shall consider the maximum expected traffic loading on the pipeline).

Pipe Outside Traffic: Cover Depth ≥ 0.8 m

Any pipe placed less than the minimum cover requirements shall be encased in concrete.

Water lines shall be placed a minimum of 3 m horizontally from any existing or proposed gravity sewer line, storm water line, septic tank or subsoil treatment system. The horizontal distance shall be measured from the outside edge of the water line to the outside edge of the line or structure.

Water lines crossing above or below sewer lines shall be placed a minimum of 0.5 m apart vertically. The vertical distance shall be measured from the outside edge of the water line to the outside edge of the sewer line. A full‐length section of the water line shall be placed at the crossing so as to maximize the distance of the joints from the sewer line. When the water line is placed below the sewer line, the water line shall be encased in concrete for a total length of 3 m centered on the crossing point.

Thrust Blocks

Thrust or anchor blocks of plain or reinforced concrete, which have been designed to resist unbalanced hydraulic forces, shall be provided at all bends, tees, tapers, in‐line stop valves and dead ends. Thrust blocks shall be designed according to the water line pressure and soil horizontal bearing capacity.

Valves


Isolation valves shall be located approximately every 500 m and shall also be located near each tee connection. The following valve types should be used for different water line diameters:

Ø < 200 mm: Gate valve using underground installation with spindle and surface box

Ø ≥ 200 mm (or two or more valves are in a group): Gate valve in a chamber

Ø ≥ 300 mm: Butterfly valve

Ø ≥ 400 mm: Bypass valve

1.3.6 Fire Hydrants The requirement for water for fire‐fighting purposes shall be determined in accordance with local regulations and Infrastructure Design Criteria.

Location of fire hydrants shall avoid lot entrances and obstruction to pedestrian movement or generally be placed at the corner of street intersections and property corners. Criteria for fire hydrant assembly spacing are as follows:

1. Limited‐Access Roads (Ring Roads), 300 m on alternating sides of the road

2. Divided Roads With Medians or Barrier Dividers, 75 m on alternating sides of the road

3. 2‐Lane Local Roads, 150 m

4. 2‐Lane Residential Roads, 120 m

5. Hydrants shall be located at a maximum spacing of 150 m in single family residential areas, 120 m in multiple family areas, and 75 m in commercial, school and industrial areas.

6. Hydrant location shall be such that the distance to any building does not exceed 75 m and not less than 12 m.

7. Hydrant shall be located within 2.5 m of finished curbing on the end of paved surface.

Distances shall be measured along road centerline or fire lane. Hydrant assemblies shall be located within public road rights‐of‐way unless otherwise approved by the fire department.

Fire hydrants leads shall be a minimum of 150 mm diameter. Hydrants shall not be connected to pipelines less than 200 mm in diameter. Hydrants shall be dry barrel type with isolation valves.

Hydrants may also be used for operational purposes, such as filling, draining, venting, and flushing of the water main. These requirements are to be considered while selecting location and type of hydrants.

1.3.7 Laterals Laterals (house connections) shall be designed to provide a flow equal to 0.3 l/s. The maximum velocity shall be no greater than 1.0 m/s. Each house connection must be installed with a flow meter used to


measure the amount of water supplied. No house connections shall be made to water lines with diameter greater than 300 mm.

Pipe material should be PE except in rocky soil where galvanized steel pipe or copper may be used. If PE pipe is used in rocky soil, the pipe must be protected by a 200 mm thick sand layer on all sides. For copper pipe; solders, flux, and pipe fittings containing lead shall not be allowed.

1.3.8 Backflow Prevention Backflow prevention shall be provided to eliminate any connection between the water distribution system and any system of pipes, pumps, hydrants, or tanks that have the potential to allow contaminated materials into the drinking water supply. To prevent cross‐contamination of drinking water, suitable backflow prevention devices must be installed. Backflow prevention devices shall comply with appropriate AWWA standard.

1.3.9 Operation and Maintenance Follow the guidelines included in AWWA Standard G200‐04: AWWA Standard for Distribution Systems Operation and Management.

1.4 Water Well Design Groundwater is the typical water supply source for communities and settlements not served by the Great Man‐made River (GMR) water supply. For the security and reliability of water supply to these communities and settlements, it is important that water supply wells be constructed to an acceptable standard of reliability and performance. A series of design criteria have been established for potable water supply wells in Libya.

Table 1—4: Water Well Design Criteria presents the design criteria governing the design and construction of potable water supply wells.

Table 1—4: Water Well Design Criteria


Approval of New Wells All new wells and well designs should be approved by the General Water Authority (GWA).

Design life Normally 25 years, except if used as a temporary source. Wells deeper than 350 m should be designed for 50 years.

Number of wells Minimum of two wells per settlement, except where there is a reliable alternative backup source of water. The number of wells should be sufficient to satisfy water demand even when there are interruptions due to maintenance. The number of wells should allow for meeting the average daily demand with the largest capacity well out of service.



Depth of wells Ideally wells should penetrate the entire aquifer, except where there are financial constraints (e.g. deep Kiklah aquifer) or a deterioration of water quality with depth. The final drill depth should be sufficient to prevent possible cave in before the placement of screens and casing.

Distance between wells To be determined by hydrogeological studies, based on pumping tests in existing wells. The distance should be sufficient to minimize interference effects between adjacent wells.

Drilling diameter Should be sufficient to allow a minimum of 5 cm gap between the borehole and the casing/screen for placing the gravel pack and cement grout.

Casing/screen material Choice of material should be based on technical constraints (well depth, aquifer and groundwater characteristics), and economic analysis. Corrosive resistant materials [e.g. glass fiber reinforced plastic (GRP), polyvinyl chloride (PVC), unplasticised polyvinyl chloride (uPVC), stainless steel (SS), etc.] to be used in areas of aggressive groundwater.

Cement grout Only neat cement grout to be used (no sand/gravel).

Well head A conductor casing of minimum length 6 m grouted into position to avoid surface contamination of the well. A concrete protection pad of minimum 1 m high around the top of the wellhead, of which 0.75 m is below ground level. The top of the casing should extend minimum 0.8 m above ground level. The casing should be locked shut/spot welded after completion to avoid contamination/vandalism of the well.

Disinfection of Wells All wells should be disinfected after completion by chlorination (sodium hypochlorite or calcium hypochlorite) at a concentration no less than 10 mg/L as free chlorine for 24 hrs. The wells should then be purged by pumping to waste until the presence of chlorine is reduced, as verified through testing or until the water no longer smells of chlorine. Note that the presence of chlorine in groundwater will tend to oxidize metals such as iron and manganese, creating dark particulates in the pump‐to‐waste water. Flushing shall continue until these particulates are removed.



Well Head Protection The well should be protected by a well house that also contains the control panel. An area of 15 m radius around the well should be fenced. In areas of shallow aquifers, no water degradation activities such as agriculture to be allowed in a 120 m radius. No cesspools or septic tanks within 60 day travel time as defined by hydrogeological studies. No use of dangerous chemicals (e.g. pesticides) within the catchment zone of the well as defined by hydrogeological studies.

Pumping Tests All production wells should be tested by:

- A variable discharge rate pumping test (min 4 steps of min 60 minutes each).

- A constant discharge rate pumping test (rate based on results of variable rate test). The length of the test to be decided based on aquifer characteristics and size of settlement to be supplied. Minimum length is 24 hours for small settlements (<1000 population), 72 hours (1000‐10,000 population), 120 hours (>10,000 population). In unconfined aquifers, the pumping test must be long enough to include delayed yield, and the final drawdown curve.

- A recovery test (continued until a minimum 95% recovery is reached, minimum test duration is 24 hours)

During the pumping tests hydrochemical parameters (including, at a minimum, pH, Temperature and Conductivity) should be monitored at regular intervals.

Water Analysis Water quality to be analyzed for all parameters in the Libyan Standard No. 82 and as included herein.

Pump capacity/type Pump capacity to be chosen based on well completion report and calculated using results of pumping tests. The capacity should not exceed 70% of the maximum pumping test rate. Pump material should be based on technical constraints and economic analysis. Corrosive resistant materials to be used in areas of aggressive groundwater. Aggressive groundwaters are usually very low alkalinity and or low TDS waters. These conditions generally do not exist in Libya.

Pump Setting Depth The pump setting depth is calculated based on the pumping test results, and allowing for a decline in the water table due to the pumping from the well, and adjacent wells. A safely margin of 5 m should be added to this depth.



Rising Main Size is determined by pump characteristics.

Rising main material should be based on technical constraints and economic analysis. Corrosive resistant materials to be used in areas of aggressive groundwater.

Dipper tube All production wells must have a 1" (25 mm) dipper tube, to enable water levels to be measured using an electronic water level dipper. The dipper tube can be hanging separately from the rising main (e.g. GI pipe), or attached to it if it is flexible (e.g. PVC/PET tube). The dipper tube should extend to minimum 10 m below the expected water level during maximum pumping rate. Corrosive resistant materials to be used in areas of aggressive groundwater.

Records A record of the construction details shall be prepared for all production wells. Recorded information must include well location; borehole diameter and depth; well casing details (diameters, materials, schedules, and depths of all permanent casings); well screen details (diameters, materials, opening widths, and depths); depth of grouted and sand‐packed intervals; original yield/drawdown; original water level.

Surface Fittings Minimum controls at the surface are flow control valve, flow meter, pressure gauge, non‐return valve, sampling tap.

Monitoring All wells to be monitored on at least a monthly basis for pumping water levels, well yield and water quality (minimum measurement = conductivity). Record to be kept of daily pumping hours and daily total flows for each well.

Emergency power supply If the existing power supply is unreliable some/all of the wells in a well field should have access to an emergency power source such as a standby automatic switchover generator.

Pump Protection The pumps should be protected by electric cut off switches. All pumps should have protection from electrical and hydraulic surges.

Spare parts Full stock of spare parts to be available so that interruptions in the supply for maintenance works are minimized.



Decommissioning of old wells

Wells to be plugged at depth with cement/bentonite if they traverse more than one aquifer. Backfilling of the well with non‐contaminated materials and protection by a surface cement or bentonite plug over the top 10 m of the well.

Protection against voltage fluctuations

Protection against voltage fluctuations by electrical surge protectors is essential for each well. To support the monitoring and operation system and to avoid electrical problems, the best protection systems should be applied such as:

- Protection against overload - Protection against short circuit - Protection against prolonged start - Earth fault protection - Temperature protection

‐ Voltage protection (protection against phase loss, protection against phase unbalance and phase sequence protection)

1.5 Surface Water, Ground Water, and Seawater Treatment

1.5.1 Purpose The purpose of the Design Criteria is to establish the common criteria for the process design of Libya HIB water treatment plants. Following is a list of goals and objectives for water treatment plant design.

1. Treatment plants for average daily demand less than 10,000 m3/day shall be designed based on the characteristics of the specific water supply. Types of process and general sizing criteria are presented in this document.

2. Water treatment plant design is dependent on the quantity and quality of water to be treated to meet finished water criteria suitable for potable water consumption.

3. Plant buildings shall be architecturally designed structures with adequate heating, ventilating, and air conditioning systems. The buildings shall be constructed of concrete or masonry with concrete roofs.

4. All treatment facilities shall be equipped with automatic changeover diesel generators suitably sized to operate the water treatment facility at average demand and to meet peak electrical load.

5. All treatment processes shall be designed for N‐1 redundancy, meaning that the facility shall be able to provide the maximum daily demand with one process train out of service.


6. Surface water treatment plants shall consist of typical conventional treatment processes such as rapid mix/coagulation, flocculation, sedimentation, filtration, disinfection and fluoridation, meeting generally accepted design standards (i.e., Health Research Incorporated Recommended Standards for Water Works, 2007)

7. Groundwater treatment plants shall consist of processes based on treating constituents in the groundwater. For Libya, the typical constituents are iron, manganese, and high total dissolved solids (TDS).

8. Electrical and Mechanical Reliability standards shall be equivalent to United States Environmental Protection Agency (USEPA) Reliability Class II.

9. All plant process basins, walkways, and stairways shall be equipped with a railing system designed with a three rails, and toe plate. The design shall be based on equivalent standards established by the Occupational Health & Safety Administration (OSHA) or National Examination Board Occupational Health & Safety (NEBOSH).

10. Pipe galleries and below grade pump rooms shall be ventilated in accordance with normal practice to reduce moisture buildup and potential for toxic gas buildup.

11. All plants shall be equipped with a Supervisory Control and Data Acquisition (SCADA) system to facilitate process control and monitoring of the facility. Flow meters shall be provided to monitor raw water, individual filtered water, and finished water.

12. Water treatment plants will have continuous online monitoring of raw water temperature, flow, turbidity, and pH; individual filtered water turbidity and flow filter headloss; finished water temperature, turbidity, pH, and chlorine residual . Plants shall also be equipped with laboratory equipment for monitoring water quality of grab samples throughout the treatment process.

13. Process design shall consider overall water conservation. Conservation of raw water supply can be achieved through the treatment and recycle of spent filter backwash water. Conservation of finished water supply for filter backwash can be achieved through the use of a combined air and water backwash system.

14. Low Pressure Membrane filtration with air backwash can be considered as an alternative to conventional water treatment with appropriate pretreatment units ahead of the membrane filtration units.

15. All treatment plants shall have primary disinfection with either ultraviolet disinfection for pathogens and chlorine for viruses, or chlorination alone. The primary disinfection shall satisfy the virus and Giardia inactivation requirements as established by the CT product method (USEPA Surface Water Treatment Rule). Secondary disinfection shall be provided via chlorination for maintaining free chlorine residual in the distribution system of not less than 0.2 mg/L as free available chlorine.

16. Water storage facilities shall be sized to meet the required contact time (CT) prior to distribution to the first customer downstream of the water treatment plant, unless the water treatment plant is the first customer. If the water treatment plant is the first


customer, then provide CT prior to sending the water back into the water treatment plant.

17. All treatment plants shall be supplied with the required service vehicles, operation and maintenance manuals and software, recommended spare parts for 2 years, workshop and training of local staff, special tools for equipment maintenance, laboratory for the required raw and treated water quality analyses, and other facilities as required.

18. All treatment plants shall be designed to allow for ease of operation and maintenance, which the contractor shall provide for a period of two years following a successful commissioning. Operation and Maintenance activities shall include routine, periodic, and preventive tasks, detailed daily recording of operations activities, materials used, etc. as recommended by the contractor or equipment manufacturers, and as indicated in the equipment operation and maintenance manuals.

1.5.2 Water Treatment Design Criteria Population and Growth Projections

Population and growth projections shall be based on the saturated population of the Third Generation Master Plan area with the water supply sources and treatment capacity according to projected population to 2025.

Water Demand

Water treatment plants shall be designed considering average daily demand and maximum instantaneous daily demand. The plant hydraulics shall be designed for maximum daily demand and future expansion. The maximum daily demand for small residential areas can range from 1.0 to 2.0 times the average daily demand. Storage capacity at water treatment plants shall be determined based on demand in the distribution system, the water need at the plant such as backwashing, service water at the plant site, and for allowing adequate contact time for disinfection. At a minimum, the plant should have 10 percent of its daily capacity available for storage over and above the volume needed for internal uses and disinfection. Fire flow demand is not included in the typical calculations for average and maximum daily water demands, but should be included when sizing finished water storage facilities.

Finished or Treated Water Quality

Finished or treated water must meet water quality standards with mean concentrations at or below the following maximum contaminant levels (MCL’s) as listed in Table 1—5. Table 1—5 also lists available treatment technologies that are commonly effective at reducing contaminants of concern. It should be noted that combinations of unit processes may be required. The source water must be sampled for the constituents below in order to establish the appropriate treatment technology.


Table 1—5: Treated Water Quality Parameters

Contaminant ‐ Microbials MCL Available Treatment Technologies(1)

Turbidity

Finished water < 0.3 NTU in 95 % of measurements

Not to exceed 1 NTU at any time

In‐line, direct, or conventional filtration. Or low pressure membranes UF or MF. Groundwater sources that meet turbidity and other standards may require no treatment through unit processes.

Total Coliforms (including fecal coliform and E. Coli)

No more than 5 % positive samples in distribution system per month

Primary disinfection for surface water systems, and maintain distribution system residual > 0.2 mg/l free available chlorine. Groundwater system may also be required to chlorinate to comply with MCL depending on source water quality.

Giardia and Viruses Achieve 3‐log and 4‐log removal

respectively

For surface water systems using conventional filtration, provide 0.5 log removal of Giardia through primary disinfection. For direct filtration, provide 1‐log inactivation of Giardia through primary disinfection. For groundwater systems, provide 4‐log removal of viruses prior to first user through chlorination, if groundwater shows evidence of fecal contamination of source.(2)

Contaminant ‐ Inorganic Chemicals

MCL Available Treatment Technologies(1)

Antimony 0.006 mg/L Granular activated carbon

Arsenic 0.01 mg/l Oxidation and then coagulation with ferric sulfate or alum (pH dependent)

Asbestos 7 million fibers/liter (longer than 10 µm)

Coagulation/filtration

Barium 2 mg/L Lime softening or ion exchange


Beryllium 0.004 mg/L Chemical precipitation

Cadmium 0.005 mg/L Ferric sulfate coagulation or lime softening

Chromium (total) 0.1 mg/L Ferric sulfate coagulation or lime softening

Copper 1 1.3 mg/L Ferric sulfate coagulation

Cyanide (as free cyanide) 0.2 mg/l GAC and chemical oxidation

Fluoride 4 mg/L Chemical precipitation or ion exchange

Mercury 0.002 mg/L Ferric sulfate coagulation

GAC

Nitrate 10 (as Nitrogen) Ion exchange or nanofiltration

Nitrite 1 (as Nitrogen) Ion exchange or nanofiltration

Selenium 0.05 mg/L

Ferric sulfate coagulation,

or Ion exchange,

or reverse osmosis

Thallium 0.002 mg/L Chemical precipitation followed by filtration

Contaminant ‐ Organic Chemicals

MCL Available Treatment Technologies(1)

Synthetic organic Chemicals (SOC’s) and

Volatile Organic Compounds (VOC’s)

Comply with the USEPA Drinking Water Contaminants and Maximum

Contaminant Levels

Generally, aeration, air‐stripping, GAC adsorption, or combinations thereof are required. Advanced oxidation may be required for certain compounds.

(1)Other treatment technologies may also apply. It may be necessary to install multiple unit processes depending

on source water quality.

(2)Conventional filtration is defined as having the following unit processes: Coagulation (i.e., chemical mixing),

flocculation, sedimentation, and filtration. Direct filtration consists of coagulation, flocculation, and filtration. In‐line filtration consists of coagulation and filtration.


Secondary Maximum Contaminant Levels (MCLs) are provided in Table 1—6. These contaminants are not considered to present a risk to human health at the maximum levels given in the table, but are related to the aesthetic quality of the water. If these contaminants are present at the levels above these standards, the contaminants may cause the water to appear cloudy or colored, or to taste or smell bad, resulting in a significant number of consumer complaints.

Table 1—6: Secondary Maximum Containment Levels

Contaminant Secondary MCL Noticeable Effects above the Secondary MCL

Available Treatment Technologies

Aluminum 0.05 to 0.2 mg/L*

colored water Coagulation & clarification

Chloride 250 mg/L salty taste Reverse osmosis Color 15 color units visible tint Conventional or direct filtration Corrosivity Non‐corrosive metallic taste; corroded

pipes/ fixtures staining pH adjustment or sequestration

Fluoride 2.0 mg/L tooth discoloration Chemical precipitation or ion exchange Foaming agents 0.5 mg/L frothy, cloudy; bitter taste;

odor Iron 0.3 mg/L rusty color; sediment;

metallic taste; reddish or orange staining

Oxidation and filtration

Manganese 0.05 mg/L black to brown color; black staining; bitter metallic taste

Oxidation and filtration

Odor 3 TON (threshold odor number)

"rotten‐egg", musty or chemical smell

Powdered or granular activated carbon

pH 6.5 ‐ 8.5 low pH: bitter metallic taste; corrosion high pH: slippery feel; soda taste; deposits

pH adjustment

Silver 0.1 mg/L skin discoloration; graying of the white part of the eye

Coagulation with ferric sulfate or alum, or lime softening

Sulfate 250 mg/L salty taste Lime softening or reverse osmosis

Total Dissolved Solids (TDS)

500 mg/L hardness; deposits; colored water; staining; salty taste

Lime softening for hardness reduction (Ca, Mg, and sulfates) or reverse osmosis for sodium, chloride, nitrates

Zinc 5 mg/L metallic taste Coagulation * mg/L is milligrams of substance per liter of water

The available treatment technologies for removal of secondary contaminants vary. Many secondary contaminants can be removed through conventional processes.


Treatment Process Operations

Table 1—7 lists basic design criteria for specific unit treatment process operations:

Table 1—7: Treatment Process Operations

BASIC TREATMENT PROCESS OPERATIONS

Rapid Mix

Design Flow Maximum Daily Flow

Allowable Types Vertical Shaft Mechanical Mixing, Jet Mixers, Static Mixers, or In‐line mixers

Velocity Gradient, G 600‐100 secs‐1

Hydraulic Retention Time 30 sec for mechanical mixing

Recommended Pre‐treatment Chemicals for reduction of:

Turbidity Aluminum Sulphate, Ferric or Ferrous Sulfate or Ferric Chloride, Polyaluminum chloride, flocculant aid polymer

Metals Ferric sulphate, Lime softening, Sodium Hydroxide for ph adjustment

Hardness Lime and/or Lime/Soda Ash to elevate pH to 10.5

General Pre‐treatment requirement ahead of Reverse Osmosis Membranes (also consult with RO system supplier)

Sulfuric acid and/or antiscalant

Flocculation

Design Flow Maximum Daily Flow

Flow‐through velocity 0.15 m/min to 0.50 m/min

Detention Time 20‐30 minutes total through minimum of two stages

Allowable Mixing Devices Axial flow propellers or turbines, flat blade turbines, reciprocating units (walking beam)

Velocity Gradient, G 70‐10 sec‐1, tapered flocculation (diminishing G) preferred

Plain Sedimentation Basins

Number of Units 2 minimum



Design Flow Maximum Daily Demand

Average Daily Demand (one unit out of service)

Detention Time 4 hours

2 hours (lime‐soda softening)

Surface loading rate 1.22 m/hr

Weir Overflow Rate 250 m3 per day per meter of weir length

Flow‐through Velocity 0.15 m/min

Minimum Sidewater Depth 3 m

Freeboard 0.5 m

Absorption Clarifiers (or other high‐rate clarifiers)

Design Size Sized by Manufacturer (Typically smaller footprint than Conventional Sedimentation Basin. Suitable for Influent Turbidities less than 30 NTU)

Tube or Plate Settlers

Design Size Sized by Manufacturer

Application Rate

< 4.8 m/hr for tubes settlers

< 1.2 m/hr for plates settlers (based on 80 % of the projected horizontal plate area

Granular Media Filters

Number of Units 2 minimum

Design Flow Maximum Daily Demand (with one unit out of service)

Filter Media Dual Media (Anthracite, Sand), Mono media (sand or anthracite) or Granular Activated Carbon (GAC)

Loading Rate 4.9 to 9.8 m/hr (2‐4 gpm/sf)

Media Depth 1 ‐ 2 m depending on water quality

Underdrains Ceramic Perforated Blocks, nozzles and false floor decking, folded steel plate,

Backwash rates Up to 49 m/hr depending on temperature and media



Backwash bed expansion 20‐30 %

Surface wash rate 1.22 to 9.76 m/hr depending on arm diameter and nozzle orientation

Air wash rate 37 to 91 m/hr air

Finished Water Clearwell

Design Flow

Maximum Daily Demand

Include system storage and fire fighting demands if not provided in distribution system.

Process Functions Chlorine Contact Time needed for C(t) (see below) plus 2 Backwash Cycles for all Filter and Process Units Requiring Water Backwash

Disinfection

Design Flow Maximum Daily Demand and lowest temperature

Minimum Contact Time

Based on effective Contact time times concentration [C(t)] required. The effective contact time is a fraction of the theoretical contact time. This fraction is dependent on : baffling, finished water pH, finished water chlorine residual, water temperature, maximum flow and minimum clearwell depth

Internal Baffling Dimension Ratio 10 Length to 1 Width

Filter Control Valves

Purpose Regulate Filter Feed and Backwash Operation

Allowable Valve Type Electrically Operated Butterfly Valve

Backwash Pump

Capacity Capable of supplying 40 m3/hr/m2 of filter area

Allowable Type

Vertical Turbine Pumps Sized to Create 30% Expansion of the Filter Bed.

Variable speed drives.

Elevated Storage Tank sufficient to hold at least 2 backwash cycles with a minimum level sufficient to provide driving head to furnish design backwash flow rate.


Other unit processes that are typically included are used in solids handling applications. This may include gravity thickeners, lagoons, dewatering equipment, and solids drying.

Treatment Plant Layout

A typical conventional water treatment plant can be configured for a campus‐style layout with separate buildings and structures for each treatment process or can be a compact design with shared‐wall construction. The layout of the facility is based on the availability of land and the existing topography.

Desalination Plants

There are two principal types of desalination plant processes, membrane desalination including electrodialysis reversal, nanofiltration, and reverse osmosis; and thermal methods including multi stage flash distillation, multiple effect distillation, and vapor compression. These types of plants may be used for sea water, brackish water in estuaries or in shallow aquifers near shorelines. For both desalination processes, seawater intake points must be located in a current environment that is directed seaward. The intake line must be situated at a depth to prevent interference with shipping operations and designed to prevent fish from entering the intake.

Reverse Osmosis (or High Pressure Membrane Process)

Pretreatment units may be required prior to the reverse osmosis process to condition the water before being treated by the membranes. Chlorine, phosphorus, and iron substantially shorten the membrane life and must be removed prior to membrane treatment. Organics must not be applied to the membranes because they cause biofouling and will also shorten membrane life.

Reverse Osmosis Membranes are spiral wound membranes offered by numerous manufacturers worldwide. For Mediterranean seawater with a total dissolved solids estimated at 30,000 mg/l, these membranes are designed to operate at operational pressures up to 60 bar.

Figure 1—1: Typical treatment process for seawater desalination is illustrated below.


Multi Effect Desalination (Distillation)

Distillation uses heat exchangers to heat the water to be treated to a boiling point. Water is boiled off of the exchanger and based though a condensing unit that produces finished water free of pathogens. Only residual chlorination of the finished water is required.

Brine Disposal

Both types of desalination plants produce brine waste that is 30 to 60 percent of the water flow. Brine should be captured in percolation or evaporation ponds. For special conditions, brine may be discharged back to the sea. These discharge pipelines must be designed with similar considerations as the intake line. The discharge pipe must terminate in an area where currents flow away from the shoreline and away from the plant intake screening system.

Pipe Materials

Table 1‐8 lists water treatment plant pipe components and the corresponding allowable material:

Table 1‐8: Pipe Materials for Water Treatment Plants

Pipe Component Allowable Material

Air Purgable Inlet and Brine Outlet Screens

5 mm Opening Size, 316 stainless steel

316 Stainless Steel Wedgewire Screen

Screen Hydraulics Designed for 50% Obstruction

Inlet/Brine Outlet Pipe (material dependent upon size)

Fiberglass Reinforced Plastic (FRP) per AWWA C950 (requires ballasting or anchors to prevent flotation)

High Density Polyethylene (HDPE) per AWWA C901 and C906 (requires ballasting or anchors to prevent flotation)

Ductile Iron (per ANSI/AWWA C151/A21.5)

Polyvinyl Chloride (PVC) (per AWWA C900)

Underground Site Pipe

Mechanical Joint Pressure Class 350 Ductile Iron Pipe(per ANSI/AWWA C151/A21.5)

Precast Concrete Cylinder Pipe (for pipes larger than 1200mm) per AWWA standards C300, C301, C302, C303, and C304)

In‐Plant Mechanical Process Pipe Pressure class 350 Ductile Iron Pipe with 125 psi Flanges

Chemical Feed Lines Non Corrosive High Density Polyethylene

JUNE 2009 REVISION NO. 02 SEWERAGE 2‐1

2 Sewerage This section presents standard design criteria for sewerage systems.

The criteria presented have been standardized to reflect typical installations. It is understood that certain situations may require deviation from the criteria herein.

2.1 Sewer Design Criteria Sewerage systems include collection of wastewater from each source, transport, including pumping stations, delivery to a treatment facility, treatment, and disposal of solids generated during the treatment process. Storage and handling of Treated Sewage Effluent (TSE) is considered part of the irrigation system and is covered in Section 4.0.

In general, sewer capacity should be designed for the estimated ultimate contributing population and the full expected development of industrial and commercial areas.

2.1.1 Sewage Flow For community wide design average wastewater flows are determined as 80% of the design average water demand. Table 2—1 lists average water and wastewater flow rates based on community population size.

Table 2—1 Wastewater Unit Flow Rates

Population [Inhabitants]

Average Potable Water Demand [Q]

Domestic Sewage Flow [Q]

Average Water Demand m3/d [Qave] (Water distribution pipe leakage, pipe flushing, lawn irrigation etc. included.)

<3,000 Q= 150 l/d/c Q= 120 l/d/c

3,000 – 20,000 Q= 180 l/d/c Q= 145 l/d/c

20,000 – 50,000 Q= 200 l/d/c Q= 160 l/d/c

50,000 – 100,000 Q= 250 l/d/c Q= 200 l/d/c

100,000 – 500,000 Q= 300 l/d/c Q= 240 l/d/c

>500,000 Q= 350 l/d/c Q= 280 l/d/c

Design peak hourly sewage flows shall be calculated by using a Peaking Factor (PF) for all sewage flows from a known or assumed tributary population, based on the Babbitt Formula, as follows:

PF = 4.25 × (Population ÷ 1000)‐1/6

The PF shall be used to project peak hourly sewage flows from tributary areas with contributing population equal to or greater than 500 persons, up to 90,000 persons. For tributary areas with fewer than 500 persons, an alternative method of estimating peak flows is allowable.


For example, the peaking factor for a population of 3,000 using the Babbitt Formula is PF = 3.5

For populations 90,000 and above, or sewage flows of 18,000 m3/d or greater, the peaking factor shall never be less than 2.0.

For concentrated commercial and light industrial area, Table 2—2 presents flow rates for selected commercial activities.

Table 2—2 Land Use Based Flows for Sewerage

Type/Activity Unit Unit Flow Rate (l/unit/day)

School – Kindergarten

Child Employee

25 50

School – Daily School

Student Employee

40 50

Institutes and medium schools Student Employee

50 50

Universities and higher Student Employee

60 50

Intern Quarters Resident 120

Institutions with beds (other than hospitals)

Employee Bed

50 200

Hospital ‐ Psychological Employee Bed

60 300

Hospital – Medical Employee Bed

60 400

Senior Care Residence Employee Resident

100 400

Care Houses (economy) Employee Resident

60 120

Public Administrative Buildings Person 50

Camps with toilet & shower Person 200

Museums and Monument Buildings

Visitor Employee

10 50

Mosques Person 30

Sports Club (with toilets only) Member 50


Type/Activity Unit Unit Flow Rate (l/unit/day)

Sports Club (with toilets and shower)

Employee Member

50 200

Cultural Club (with toilets only) Employee Visitor

50 10

Recreational Club (with toilets only)

Employee Visitor

50 25

Factories & Commercial Varies according to industry type

Parks (with toilets only) Employee Visitor

50 10

Offices (with toilets only) Employee Visitor

50 10

Hotels Room Employee

380 50

Exhibition Halls Employee Visitor

50 20

Airport Passenger Employee

18 54

Petrol (Fuel) Stations Car 100

For other commercial and industrial sewage flow projection, a detailed evaluation is required by type on a case‐by‐case basis subject to occupancy regulations.

2.1.2 Hydraulic analyses Hydraulic analyses shall be carried out using approved computer modeling software. Acceptable models are Infoworks, SewerCAD, Mouse Model, InfoSewer, and other equivalent commercially available models.

Roughness coefficients based on the pipe material as shown in Table 2—3 shall be used. The roughness coefficient is a measure of the variation and magnitude of protuberances on the interior surface of the pipe. The roughness therefore is a function of the pipe material, age, and condition. Poor pipe conditions are to be assumed for sewage system designs.


Table 2—3 Typical Roughness Coefficients

Pipe Material

Manning’s Coefficient, n

Normal Maximum

uPVC 0.010 0.013

GRP 0.010 0.013

HDPE 0.010 0.018

RCP 0.012 0.016

DIP with

mortar lining 0.012 0.016

2.1.3 Flow Velocities The design flow velocity limits are listed below.

Table 2—4 Minimum and Maximum Velocities in Sewer Pipes

Pipe Description Minimum Velocity

(m/s) Maximum Velocity

(m/s) Design Velocity

(m/s)

Gravity pipe 0.5 2.5 0.75

Pressure pipe 0.6 to 1.0 2.5 1.5

2.1.4 Depth of Flow The following table shows the recommended depth of flow in gravity sewer lines. The ratio d/D is the ratio of the flow depth (d) to the nominal pipe diameter (D).


Table 2—5 Minimum and Maximum Depth of Flow in Sewers at Peak Flows

Description Maximum (d/D) Minimum (d/D)

Trunk sewer lines 0.75 0.50

Main and lateral sewer lines 0.85 0.50

2.1.5 Pipe Gradients In order to achieve the required minimum velocity in sewer lines, pipes should be designed by observing the minimum gradients listed in the table below.

Table 2—6 Pipe Gradients

Pipe Diameter (mm)

Minimum Gradient (m/m)

(Velocity 0.75 m/s)

200 0.00500

250 0.00370

315 0.00270

400 0.00200

500 0.00150

600 0.00120

700 0.00100

800 0.00085

900 0.00070

1000 0.00060

1100 0.00055

1200 and larger 0.00050


2.1.6 Pipe Materials Sewer pipe materials have been selected to be consistent with local standard practices, based on economics and local availability. The following materials shall be used for various pipe sizes:

(1) For sewer mains equal to or less than 315 mm in diameter, uPVC shall be used. For sewer mains larger than 315 mm in diameter, GRP shall be used. Other corrosion resistant materials, such as PVC greater than 315 mm, high density polyethylene pipe (HDPE) or vitrified clay pipe (VCP) may be considered.

(2) For pressure mains, GRP, HDPE or PVC shall be used. DIP with mortar lining or ceramic epoxy lining may be considered for special circumstances.

2.1.7 Minimum Cover Requirements The minimum cover recommended is 1.2 m above the pipe crown, in order to protect from external loads. If the available cover is less than 1.2 m, then additional protection such as full concrete encasement or the use of concrete protection slabs shall be provided. In special areas with heavy loading, specific protection may be required based on structural evaluations.

The actual cover required for construction and access may be greater than that required solely for structural integrity. For example, the minimum cover required by the physical dimensions of a typical access manhole is 2 m above the pipe crown. However, for small pipes less than or equal to 315 mm in diameter, the required cover may be less than 1.2 m. If inspection chambers are installed rather than manholes, 1.0 m of cover will suffice.

The maximum cover depth recommended is approximately 10 m. This maximum depth is consistent with typical pipe installation standards and manufacturer recommendations. Should the actual cover be greater than 10 m, pipe materials and loads should be evaluated and a higher strength class of pipe utilized.

For pipes installed at less than these minimum values or at excessive depths, concrete encasement may be required to protect the pipe from damage. Alternatives of different pipe size at a different slope should be considered before designing the pipelines outside of the specified depth ranges.

In all cases, the pipe minimum and maximum depths shall be in conformance with the pipe manufacturers’ recommendations

2.1.8 Utility Crossings Utility crossings for this project shall follow the guidelines shown in Table 2—7.

Table 2—7 Utility Crossings for Sewer Pipes

Parameter Minimum Criteria

Vertical Clearance - 50 cm; if less than 50 cm, use concrete saddle and provide

concrete encasement to first joint on each side of crossing



Horizontal Clearance - 3.0 m

- Where available corridor space is limited, minimum clearance may be reduced to 1.2 m assuming structures can overlap into adjacent corridors.

- If in same trench, place other utility on separate bench on undisturbed soil above sewage line

Potable Water Lines Always place sewage lines below potable water lines

Pipes shall be aligned to cross under roads at 90 degrees or perpendicular to the road.

2.1.9 Manholes Manholes are required to provide access to the sewer mains. They are also provided at each change in direction (vertical or horizontal), change in diameter, and connection of two or more lines. Sewage manholes are to be installed a maximum of 100 m apart. Sewage manholes shall be constructed of reinforced concrete with GRP lining for corrosion protection. These structures shall be circular in shape and designed in accordance with the standards provided in Table 2—8.

Table 2—8 Sewer Manhole Design Criteria

Description Standard

Maximum Spacing between manholes

100 m

Benching Minimum 0.50 m width on at least one side of flow channel. Ladder stops to be incorporated into surface.

Manhole Access Access by electric winch and tripod or portable ladder. Ladder stops to be incorporated in benching for emergency access. No built‐in ladder rungs or permanent ladders.

Manhole Frame and Cover Circular opening 0.60 m minimum diameter. Cover and frame to be machined and tagged to prevent rocking. All covers and frames in roadways to be rated for maximum vehicle loads.

Access Shaft Diameter 1.0 m

Length 2.5 m maximum


Description Standard

Barrel Diameter 1.5 m except as otherwise noted. Based on pipe diameter plus minimum benching of 0.5 m on one side

Safety Chains Provide on all manholes with pipe diameter 600 mm or larger

Materials of Construction:

Access Shaft

Top Slab

Barrel

Bottom Slab

Benching

Lining

Exterior Corrosion Protection

Mass Concrete (no reinforcement)

Reinforced concrete

Mass Concrete (no reinforcement)

Reinforced concrete

Granolithic concrete base

GRP factory‐fabricated and hand lay‐up seams.

Bituminous impregnated membrane with flexible fabric

Testing Hydrostatic and Infiltration (as specified)

Alternative manhole designs are required where there are multiple pipeline crossings.

In general, gravity sewers alignment shall be adjusted such that all manholes are located outside of vehicular travel lanes. Where space for construction corridors is limited, manholes may be placed in paved shoulders.

2.2 Pumping Stations Pumping stations are required when sewerage collection network depths exceed the practical or economic constructability limit. Sewerage facilities will typically consist of gravity driven systems; however, due to topography and the need to limit sewer depths to a practical maximum, pumping stations may need to be included in the system.

All sewage pressure pipes within the site limits of the pumping station shall be GRP with minimum pipe stiffness of 10,000 N/m2. Foul air pipes may be either uPVC or GRP.

2.2.1 Pumping Station Type The design philosophy includes the minimization of the total number of sewage pumping stations in the collection system. Where pumping is required, the number of times a given flow is pumped should also be minimized.


Three types of sewage pumping stations shall be used: (1) submersible stations for small to medium size facilities, (2) wet well‐dry well stations for large facilities, and (3) screw pump stations in situations where the required head is just to lift into a higher elevation gravity flow pipe.

Pumping stations shall be designed to handle flows greater than or equal to the projected peak influent flow rate which is determined by applying the Peaking Factor to the average flow. Peak flows shall be validated using hydraulic modeling software with accurate modeling of the actual sewer collection system.

Wet well sizing is a function of the incoming flow, the control strategy for the station, the selected pumps, whether single speed or variable speed drive, and the number of starts per hour permissible for the pumps. Recommended cycling frequency depends on the type of pump being used, the motor size, and pump operating efficiency. For design purposes, submersible pumping stations shall have a minimum cycle time of 6 minutes or a maximum of 10 starts per hour. Pump controls shall be based primarily on water elevations in the wet well of the station. A supervisory control and data acquisition (SCADA) system shall be used to ensure appropriate cycling of individual pumps based on run times. Constant speed pump operation shall be by simple start‐stop switches actuated by wet well elevation with separate float switches for high and low wet well alarms and shutoff. Variable speed pumps should be provided to maintain a set water level in the wetwell.

2.2.1.1 Wet Well Volume For constant speed pumps, wet well volume is calculated based on cycling frequency when inflow to the station is 50 percent of the pumping rate with a single pump operating.

The wet well volume shall be calculated from the basic formula:

CT = [V/(D‐Q)+(V/Q)]

where

D = Pump rate (m3/min.)

Q = Inflow rate (m3/min.)

CT = cycle time (min.)

V = volume (m3)

Since “minimum” cycle time is of concern (Q=D/2), the formula reduces to V = CT x Q/4.

2.2.1.2 Wet Well Depth The operating depth of wet well is a function of the following:

1. Required submergence to prevent vortexing in the pump suction piping or the pump inlet, which may cause unbalanced loading on impellers & bearings, thereby reducing pump life.

2. The Net Positive Suction Head Required (NPSHR) plus a 1.5 meter margin. The NPSHR is based on the particular pump, impeller selection, and requirements provided by the pump manufacturer.


3. Priming: The minimum wet well level must be set 150 mm above the top of the pump volute.

4. The elevation of influent sewer shall be designed to prevent turbulence and air entrainment in the wetwell.

5. High liquid level in the wet well shall be set at 0.8 times the inlet pipe diameter above the invert. This allows the inlet pipe to be emptied frequently, preventing buildup of settled material in the gravity inlet pipes.

The required submergence refers to minimum liquid level above a vertical pump inlet, flare inlet, or fitting, and above the centerline of the flare if positioned horizontally.

The minimum submergence determination, priming, and NPSHR shall be verified during the wet well sizing.

2.2.2 Pump Selection Pump selection should be made to optimize conditions over the minimum, average, and maximum projected range of flows. Selection is made to minimize holding times in the wet well before pumping and to maximize efficiency. Actual pump selection is made after a system head capacity curve is developed for the proposed installation. The following are to be considered:

1. Required range of flows

2. Range of friction coefficient values for old and new pipe

3. Range of static head, note that the high wet well elevation is to be used for the pump design rating point

4. Number of pumps based on pump selection POR and AOR

5. Number of standby pumps

6. Operating and control strategy

7. Efficiency

8. Potential for upgrading capacity

All pumping stations shall have a minimum of two pumps. The pumps shall be lead‐lag design with each pump automatically alternating as lead pump. With this operation, both pumps will accumulate approximately the same number of run hours over time. A two pump system must be designed mechanically and electrically for the second pump to operate in parallel with the lead pump.

If screw pumps are used, a minimum of two pumps shall be installed. Screw pumps automatically pump with a variable output to match the incoming flow (up to a maximum capacity). Pump selection is primarily a function of number of pumps, pump maximum capacity, number of flights, and lift.


2.2.3 Pumping Station Structures Pumping station structures shall be designed to ensure a safe working environment for operation and maintenance staff, as well as to maximize performance and to minimize construction and operation costs. The following shall be incorporated:

1. Wet wells shall be isolated from dry wells and/or superstructures by impermeable walls.

2. Independent ventilation systems for shall be used for the wet well and the dry well to meet applicable standards.

3. Provisions shall be made to facilitate removing pumps, motors, and other mechanical and electrical equipment.

4. Suitable, separate, and safe means of access shall be provided to dry wells and to wet wells.

5. Wet wells and pump suction inlets shall be configured to minimize turbulence. Trench type wet wells shall be used.

6. A minimum of two wet wells shall be used except for pumping systems with a capacity less than 35 L/sec or self‐cleaning trench wet well if approved

7. Wet well controls shall be of the encapsulated float type as a minimum. More sophisticated control may be considered. In all cases, control sensors shall be located away from turbulence of incoming flow and pump suction. Where floats are used they must be installed on a Type 316L stainless steel pipe. No hanging floats are acceptable.

8. All pumping stations shall provide a valved connection point downstream of the pump isolation valves to allow temporary bypass pumping

9. Wet wells shall be GRP lined with factory fabricated materials

2.2.4 Surge Protection Surges can be generated in the sewage force main following power failures, pump starting, or stopping and sudden valve operations. The need for surge limiting equipment to protect the force main due to possible transient pressure variation shall be considered. The calculation of surge shall be carried out by appropriate methods and using the relevant general equations and surge flow calculation software according to the conditions specified by the designer and based on the most unfavorable operating conditions. Where surge protection is found to be necessary, the designer shall size and specify the appropriate surge protection equipment. Surge tanks are the preferred method and can be bladder tanks or air tanks.

2.2.5 Electrical and Instrumentation Systems All pumping stations shall be designed and constructed based on international principles. The following provisions shall be included:

1. Supply and control circuits shall allow for disconnection from outside the wet well. Terminals and connectors shall be protected from corrosion through proper location and/or the use of water tight seals. Separate strain relief.


2. Properly sealed motor control panels shall be provided.

3. Ground fault interruption protection shall be provided.

4. Power cords shall be designed for flexibility and serviceability under conditions of extra hard usage and such that field connections are facilitated.

5. Each sewage pumping station shall have a flow meter with instantaneous flow indicator.

Instrumentation systems shall be consistent with other existing systems and integrated into the system wide centralized operational management system (SCADA control system).

The SCADA system shall be compatible with the existing control and monitoring systems. Typically, the SCADA system will be monitored and compiled at the main master system locations, although remote stations may also be incorporated into the system.

2.2.6 Odor Control Odor control measures shall be provided to ensure that noxious gases and odors are in concentrations lower than the detection level. Chemical odor control systems shall comprise of chemical scrubbers with packed counter current or cross current, two or three stage chemical type and/or a bulk activated carbon deodorizer. Biofilter odor control is also acceptable and preferable in locations where chemical replacement may not be reliable. Ventilation shall be designed for one complete air change per hour consistent. Ventilation of submersible pump wet wells shall be a minimum of 12 air changes per hour.

2.2.7 Rising Mains Rising mains shall be sized to maintain velocities with an acceptable range for a variety of flow conditions. Rising main pipe diameters shall not be less than 200 mm. Selection of the diameter is dependent on the maximum and minimum flow rates required through the pipe, and the characteristics of the pipe (length, material, and route). The head loss in the system should be minimized.

Minimum and maximum velocities for sewer rising mains have been established as 0.6 to 1.0 and 2.5 m/s, respectively, with a target design velocity of 1.5 m/s. The maximum velocity restriction is related to minimizing the effects of scour on the interior of the pipe as well as minimization of friction head losses. The design velocity is based on the ability to re‐suspend settled solids within the rising main. The minimum velocity must be achieved with only one pump in operation since this will be the condition during low‐flow periods.

2.2.8 Air Valves and Washouts The raising mains shall be equipped with the following valves for facilitating the operation, control, and maintenance:

1. Air and Vacuum Valves: These valves shall be provided at summits along the pipe profile and along long stretches with uniform slope to purge out accumulated air in the pipe system. Air release and vacuum relief valves are often needed along transmission mains and may sometimes be unavoidable in sewage force mains. Air must be bled slowly from high points to prevent (1) “air binding” and (2) the reduction of the cross section of the pipe at high points. Vacuum conditions must be prevented when the pump head drops quickly (as in power failures) to prevent column separation and at extreme high points in pipelines to prevent potential pipeline collapse due to vacuum.


Vacuum relief valves can be as large as one‐sixth of the diameter of the transmission main, whereas air release valves may be as small as one‐fiftieth of the diameter of the pipe.

2. A combination of air and vacuum valves shall be provided at appropriate locations for quick air entry or vent to prevent cavitations and facilitate quick filling of the pipe. In general, air‐valves are to be provided at crest points, changes in elevations and in case of constant rising mains having moderate slope, at a maximum spacing of 600 m.

3. Washout valves: These valves will be provided at low points or sags along the pipe profile. These valves facilitate flushing, repair or maintenance of the pipe wherever necessary.


5. Isolating Valves with diameter smaller than 300 mm shall be solid wedge or double revolving disc gate valves and larger diameter shall be eccentric plug valves or double revolving disc gate valves.

6. Non‐Return Valves: These valves will be provided in the pumping station to prevent a reverse flow into the pumps and shall be rubber flapper type with position indication and backflow device.

All valves not located in a pumping station structure shall be installed inside reinforced concrete valve chambers, consisting of an access manhole, vent, a ladder, and a sump.

2.2.9 Emergency Power Supply All pumping stations shall be provided with back‐up, engine‐driven electrical power generators sized to power 100 percent of the rated pumping station capacity.

2.2.10 Pumping Stations Operations and Maintenance 1. Pumping station buildings shall be architecturally designed structures with adequate

heating, ventilating, and air conditioning systems. Prefabricated structures shall not be allowed. All buildings shall be of concrete or masonry construction.

2. Electrical and Mechanical Reliability standards shall be equivalent to USEPA Reliability Class II.

3. All pumping station wet wells, walkways, and stairways shall be equipped with a railing system designed with three rails and a toe plate. The design shall be based on standards established by the US Occupational Health & Safety Administration (OSHA) or UK National Examination Board in Occupational Safety and Health (NEBOSH).

4. Pipe galleries and below grade pump rooms shall be force ventilated (powered in and out) sufficiently to minimize potential for toxic gas buildup. Unless otherwise directed,


all buildings and structures shall comply with US National Fire Protection Association 820 standards.

5. All pumping stations shall be equipped with a Supervisory Control and Data Acquisition (SCADA) system to facilitate control and monitoring of the facility. Full automation shall be provided where pumps or equipment are modulated by remote control inputs.

6. All pumping stations shall be supplied with the required service vehicles, operation and maintenance manuals and software, recommended spare parts for 2 years, workshop and training of local staff, special tools for equipment maintenance, and other facilities as required.

7. All pumping stations shall be designed to allow for ease of operation and maintenance, which the contractor shall provide for a period of two years following a successful commissioning. Operation and Maintenance activities shall include routine, periodic, and preventive tasks, detailed daily recording of operations activities, materials used, etc. as recommended by the contractor or equipment manufacturers, and as indicated in the equipment operation and maintenance manuals.

JUNE 2009 REVISION NO. 02 SEWAGE Treatment 3‐1

3 Sewage Treatment

3.1 Purpose The purpose of the principal Design Criteria is to establish the common criteria for the process design of Libya HIB sewage treatment plants. Following is a list of goals and objectives for these treatment plant projects. Contractors shall provide evidence of compliance with each of these objectives in their proposals.

1. Sewage treatment plant processes shall be based on the following flow criteria:

(a) Up to 2,000 m3/d: Aerated lagoons (AL) or Stabilization Ponds (SP)

(b) 2,001 to 12,000 m3/d: Extended Aeration (EA)

(c) 12,001 to 50,000 m3/d: Oxidation Ditches (OD)

(d) Over 50,000 m3/d: Conventional Activated Sludge (CAS)

2. CAS sewage treatment plants shall have waste activated sludge (WAS) thickening with gravity‐belt thickeners prior to anaerobic digestion of WAS and primary sludge. Final dewatering shall be with belt filter presses.

3. EA and OD plants with 30 day solids retention time can be constructed without formal sludge digestion systems. With solids retention times <30 days EA, and OD plants will require pre‐thickening of sludge with picket fence thickeners prior to aerobic sludge digestion, and final sludge drying beds for plant sizes less than 20,000 m3/day or belt filter press dewatering for plant sizes > 20,000 m3/day. Where the STP is located close to populated areas, belt filter presses may be used to eliminate the risk of odors from the sludge drying beds.

4. Plant buildings shall be architecturally designed structures with adequate heating, ventilating, and air conditioning systems. Prefabricated structures will not be allowed. All buildings shall be of concrete or masonry construction.

5. All EA, OD, CAS, and AL mechanical treatment facilities shall be equipped with automatic switching diesel generators suitably sized to operate the sewage treatment plant at design peak flows and loadings and to satisfy peak electrical load for all operating equipment, lights, and controls.

6. All plants with anaerobic digestion shall have dual fuel generators to allow the use of digester gas for power generation at the plant.

7. Electrical and Mechanical Reliability standards will be equivalent to USEPA Reliability Class II. Biological reactors and clarification shall have a minimum of two tanks for each process component. For all facilities larger than 15,000 m3/day, full treatment shall be provided with any one process tank out of service. No processes shall be bypassed under any reliability condition.


8. All plant process basins, walkways, and stairways shall be equipped with a railing system designed with three rails and a toe plate. The design shall be based on standards established by the US Occupational Health & Safety Administration (OSHA) or UK National Examination Board in Occupational Safety and Health (NEBOSH).

9. Pipe galleries and below grade pump rooms shall be force ventilated (powered in and out) sufficiently to minimize potential for toxic gas buildup. Unless otherwise directed, all buildings and structures shall comply with US National Fire Protection Association 820 standards.

10. All plants shall be equipped with a Supervisory Control and Data Acquisition (SCADA) system to facilitate process control and monitoring of the facility. Full automation shall be provided where processes or equipment are modulated by inputs from field instruments.

11. Water reuse will be planned for all sewage treatment plants in Libya, unless specifically indicated otherwise. All treatment facilities shall be equipped with effluent filtration by disc filters, continuous backwash sand filters or membrane filters.

12. Each plant shall be equipped with a plant water system for washdown purposes, and other uses. The system should be a non‐potable water system using filtered treatment plant effluent as a water source. The system shall include a hydropneumatic system using either air tanks and compressors or bladder tanks

3.2 Sewage Treatment Design Criteria Minimum number of process units: Treatment plants shall be required to have the following minimum number of process units or unit operation.

• Coarse Screens for plants over 2000 m3/day: (Minimum 2 active and one bypass)

• Fine Screens: 2 minimum

• Traveling bridge type rectangular aerated grit chambers: Single grit chamber for lagoons and package treatment plants <2000m3/day and two parallel grit chambers for EA, OD, and CAS sewage treatment plants.

• Conventional velocity controlled grit chambers (SP): 2 minimum

• Primary Clarifiers (CAS): 2 minimum

• Aeration Tanks (CAS,OD,EA plants): 2 minimum

• Filter disc chambers or concrete filter chambers: 2 minimum

• Pump and air blower systems will have one standby unit equal in size to the largest pump or air blower in the system

1. All treatment plants shall be supplied with the required service vehicles, operation and maintenance manuals and software, recommended spare parts for 2 years, workshop and training of local staff, special tools for equipment maintenance, laboratory for sewage and sludge testing, and other facilities as required.


2. All treatment plants shall be designed to allow for ease of operation and maintenance, which the contractor shall provide for a period of two years following a successful commissioning. Operation and Maintenance activities shall include routine, periodic, and preventive tasks, detailed daily recording of operations activities, materials used, etc. as recommended by the contractor or equipment manufacturers, and as indicated in the equipment operation and maintenance manuals.

3. The Treatment plants will be specifically designed to treat to water reuse standard

quality and monitored for performance daily.

4. All treatment plant processes will be designed in such a manner that discharge quality will be maintained with service outage in any of the major equipment groupings including pumps, air blowers, and mechanical mixers, sludge thickening and dewatering devices. For each surface aerator and aerator mixer there shall be one extra mixer in each aeration basin or aerobic digester to assure compliance with one slow speed line shaft aerator or aerator mixer out of service.

3.2.1 Population and Growth Projections Population and growth projections shall be based on the saturated population of the Second Generation (or Third Generation) Master Plan area with sources and requirement according to projected population till 2025.

3.2.2 Sewage Flow Generation Sewage treatment plants shall be designed to accommodate both the average daily flow and peak hourly flow. Treatment plant hydraulic systems shall be designed to accommodate the peak hourly flow. The peak hourly flow can range from 2.0 to 4.0 times the average daily flow rate of the facility.

The peak flow factor shall be based on the Babbitt formula listed in Section 2 and as calculated below in Table 3—1. For populations above 90,000, the maximum design flow shall be based on a 2.0 peaking factor. For populations less than 1,500, the design peak flow shall be based on a peaking factor of 4.0.

The following table presents a basis for calculating design flows for sewage facilities that include pipelines, pumping stations, and sewage treatment plants.

Table 3—1. Calculated Peak Flow Factors for Specific Populations

Population Sewage Flow Peak Flow Factor

< 1,500 Q < 220 m3/d 4.0

2,000 Q = 290 m3/d 3.78

5,000 Q = 725 m3/d 3.25

10,000 Q = 1450 m3/d 2.90

20,000 Q = 4,000 m3/d 2.58


Population Sewage Flow Peak Flow Factor

50,000 Q = 10,000 m3/d 2.21

≥ 90,000 Q = 18,000 m3/d 2.00

3.2.3 Sewage Loadings Table 3—2 lists typical sewage loading values for planning and design purposes. Whenever possible, laboratory analysis of the sewage shall be made to establish actual values for design.

Table 3—2. Typical Sewage Loading Values

Parameter Value

BOD5 60g/cap‐day

TSS 80g/cap‐day

NH3 10g/cap‐day

TP 1.2g/cap‐day

COD 150g/cap‐day

pH 6.5 ‐ 7.5

TKN 13 g/cap‐day

FOG 30g/cap‐day

3.2.4 Design Discharge Quality Limitations Table 3—3 lists sewage design discharge quality limitation values:

Table 3—3: Sewage Discharge Quality Limitations

Parameter Value

BOD5 10 mg/l

TSS 10 mg/l

NH3 1 mg/l

TP 10 mg/l

pH 6.0‐9.0

TN 20 mg/l

FOG 5 mg/l

Total Coliform MPN < 23/100 ml


3.3 Site Specific Design Considerations Sewage treatment plants shall be sited for full access to all process units, equipment, and ancillary facilities. Following is a list of considerations in site specific treatment plant design.

1. Altitude of site. This is important to properly design biological and oxygen transfer systems in activated sludge sewage treatment plants. Aeration compressors shall be sized for the ratio of actual oxygenation rate to standard oxygenation rate. Standard oxygenation rates assume operation at sea level and 20 deg C water temperature.

2. Proximity to floodplains. Treatment sites must not be vulnerable to flooding and should be specifically designed to operate and remain in regulatory compliance during flood events as great as that with a 4 percent probability (25‐year flood). For events with less than 1 percent probability of occurrence in any given year (100‐year flood), treatment facilities shall be protected from damage during the flood, but are not required to meet effluent quality limitations.

3. Temperature of influent sewage. Water temperature greatly influences the biological reactions that occur in the activated sludge aeration basins. Higher water temperatures (up to 35 deg C) provide higher biological kinetics. At low water temperatures (below 20 deg C), bacterial growth is hindered. Process calculations shall be performed for the maximum monthly average water temperature and minimum monthly average water temperature.

4. Availability of process equipment. All equipment shall be provided by vendors who can readily service their equipment installations in Libya. While limited equipment is produced in Libya, it is preferable that equipment be provided where spare or replacement parts can be delivered within two business days.

5. Ambient considerations. With potential for dust and sand storms and ambient temperatures as high as 50 degrees C, certain process equipment including dry pit pumps, aeration blowers, chemical feed systems and generators, shall be placed in ventilated buildings. For installations in the coastal areas, shade structures may be allowed if they have barriers protecting the equipment from wind storms.

6. Proximity of population. Sewage treatment plants shall be sited such that they are a minimum distance of 1000 m from populated areas. If this cannot be accomplished because of site availability, treatment plant design shall include mechanical odor control measures that can include containment and odor scrubbing of off‐gases from plant pumping stations, headworks systems, primary clarifiers, and anaerobic sludge handling processes at a minimum. Alternative sludge drying systems may be required if odors cannot be contained within the site. Odor control methods may include biofiltration, granular activated carbon, or multiple stage chemical scrubbers (for extreme cases only).

7. Structural foundation design. Subsurface geotechnical investigations shall be conducted for treatment plant designs to enable the development of site specific design criteria. For facilities in areas of soft or expansive soils, water bearing structures shall incorporate the use of friction piles, bearing piles, or equivalent structural supports.


Foundation design shall be in accord with the recommendations made in the geotechnical investigations report.

8. Proximity of water supply wells. Sewage plants shall not be sited within 300 m of potable water supply wells.

9. Minimum Flows. Minimum flows will be considered in channels, pipelines, and process mechanical systems operating ranges.

3.4 Treatment Process Design Criteria The following tables list design criteria for different sewage treatment processes.

3.4.1 Liquid Process Table 3—4. Liquid Process Criteria

Coarse Bar Screens for all plant types

Opening Size Coarse Screens 15 to 25 mm

Location Influent pump station, headworks bypass channel

Head Loss through Clean Screen 0.3 m

Operation

Manually cleaned bar racks shall be limited to facilities with capacities less than 15,000 m3/day with larger facilities being the mechanical type. Drum screens and Huber Rakmax screens mechanical screens are acceptable

Fine Screening for CAS, EA, and OD systems

Opening Size Fine Screens Range 6‐10 mm (fine)

Maximum Head Loss, clean screen 0.3 m

Screen Types

Bar screen, step screen, band screen, or perforated plate screen. Step screens shall include a continuous flushing system for the bottom step. Drum screen with 2.5‐5mm opening size (Plants larger than 15,000 m3/day‐ OD and CAS only)

Screen and wetted parts 316 Stainless Steel or Duplex Steel

Auxiliary Equipment Screenings conveyor and screenings compactor. Systems to be a simple as possible with screenings dropping from screens into containers where practical.

Operation

Coarse screens followed by fine screens Automatically cleaned. Screen systems to be simple, drop directly to containers. Provide screenings washer compactor systems on screens 12 mm and smaller opening size. Use conveyors only where required.


Underwater Bearings May be allowed for selected screens including Mahr headworks screen, Huber Rakemax Screen, and perforated plate screens.

Basin coating system All concrete structures shall have a corrosion protective coating that extends from 0.33m below the water surface to the top of the tank.

Aerated Grit Chambers

Design Hydraulic Detention Time 10 min at peak hourly flow

Minimum Depth 2 m

Length to Width Ratio 3:1 or more

Aeration Coarse Bubble Diffused Aeration

Grease Removal Grit removal and grease removal shall be integrated in an aerated channel system similar to the Huber traveling bridge system.

Grit Pump Centrifugal recessed impeller of hardened materials, or Air Lift for Traveling Bridge

Air Blowers for aerated grit chamber Tri‐lobe positive displacement air blowers

Grit Washer 316L stainless steel and be capable of producing grit with less than 3‐5% organics in the treated grit for all grit systems.

Primary Clarifiers (CAS only)

Treatment CAS Only > 50,000 m3/d

Configuration Circular

Surface Overflow Rate – average (peak) 30‐50 m3/m2‐day (80‐120 m3/m2‐day)


Weir and Launder System Weir plate and peripheral launder

Weir Loading Rate – average (peak) 125‐250 m3/m‐day (250‐500 m3/m‐day)

Mechanism Type Center or Rim Drive with spiral blade collectors

Scum Skimmer Single scum skimmer with 1200 mm wide beach. Scum system will include chopper pumps with recirculation provision.

Spray Systems Primary clarifiers will have spray systems for scum removal

Scum Baffle 600 mm depth

Sidewater depth 3.5 m to 6 m

Basin coating system All concrete structures shall have a corrosion protective coating that extends from 0.33 m below the water surface to the top of the tank.


Aeration Basins (CAS, EA, OD)

Design Hydraulic Detention Time 4‐8 hrs (CAS); 20‐30 hours (EA ); and 15‐30 hours (OD )

Design Mixed Liquor Suspended Solids (MLSS)

1,000‐3,000 mg/L (CAS); 2,000‐5,000 mg/L (EA ); and 3,000‐5,000 (OD)

Design Solids Retention Time (SRT) 3‐15 days (CAS); 15‐30 days (OD ); and 20‐40 days (EA)

Design Food to Microorganism Ratio (F/M) (kg BOD/kg MLVSS‐d)

0.04‐0.10 (OD and EA ) and 0.2‐0.4 (CAS)

Types of Aeration Systems

Bridge Mounted Aerator Mixers (CAS, EA). Brush or Disk Rotor and Orbal Aerators (OD)

Fixed slow speed or two‐speed surface aerators mounted on concrete bridges or bottom mounted aerator and sparge ring mounted on concrete platforms for CAS and EA systems. Fine bubble diffusers are not acceptable due to diffuser interference with cleaning of basin bottoms.


Secondary Clarifiers

Configuration Circular

Surface Overflow Rate – average (peak) 16‐28 m3/m2‐day (CAS); (40‐64 m3/m2‐day) (EA and OD) Long SRT systems produce lower density sludge requiring longer settling time clarifiers for EA and OD Systems

Solids Loading Rate – average (peak)

4‐6 kg/m2‐hour (CAS 2‐4 kg/m2‐hour (5‐7 kg/m2‐hour) (EA and OD). EA and OD sludge settles poorly and the loading rate has to be lower than for CAS based on lower solids retention time (SRT).


Weirs and Launder External perimeter type. Launders to be concrete with FRP weirs and scum baffles.

Scum Baffles 600 mm depth, minimum 1200 mm wide scum beach

Mechanism Materials All mechanism elements below water line shall be 316 L stainless steel

Scum pump system Chopper pump system with provisions with recirculation mixing system for improving pumpability of mixture.

Scum spray system Spray system required for scum removal

Clarifier baffles Clarifiers to be equipped with impinging type baffles


Sludge Collector Mechanisms

Spiral scraper with center drives or rim drives.

Suction Type Similar to Rapid Sludge Return (RSR) Clarifier or spiral blade type. Direct suction type through slotted tapered tube.


Filters

Type of Filter

Continuous Backwash Upflow Filtration (Fluidized bed type) or Stainless Steel or Fabric Disc Filters designed in accordance with manufactures recommendations. These are designed for maximum flow through the system.

Hydraulic Loading Rate 15 m3/m2‐h for Fabric Disc Filter at max flow 15 m3/m2‐h for Fluidized bed Filters at max flow

Disc filter submergence 60% maximum at max flow or per manufacturer recommendations

Minimum Sand Media Depth 2.0 m

Single Filter Module Dimension 2 m x 2 m (fluidized bed)

Tankage Reinforced concrete


Disinfection

Method Ultraviolet Radiation (UV)

Minimum dosage 80 m Joules/cm2

Discharge limit Total Coliform: <23 colonies per 100 ml

Enclosure UV systems shall be housed in site‐built buildings


Supplemental Disinfection

Method Sodium Hypochlorite (12.5% solution)

Minimum dosage 2 mg/l at peak effluent flow rate

Tank Material, Size Cross‐linked Fiberglass Reinforced Plastic (FRP), 3 m3 or 1 week supply whichever is greater


3.4.2 Liquid Process Hydraulic Systems Table 3—5. Liquid Process Hydraulic System Criteria

Inlet Structures and Flow Splitting

Influent structure (Concrete) Influent structures shall have concrete covers with positive odor control.

Flow split structures (Concrete) Provide weir slide gates or flumes for proportional split of flow to individual process units.

Liquid Process Hydraulic Flow Distribution

Design Flow Maximum Flow

Channel Construction Concrete with Open Grating Above

Screening Channels features

Isolation gate valves upstream and downstream of each screenAbility to dewater any portion of the screening channel that can be isolated Screen channel shaped to sloped to prevent grit accumulation at lower flowrates.

Channel Velocity, unaerated (minimum) Raw sewage 0.8 m/sec; settled sewage 0.3m/sec

Gravity Pipe Velocity (minimum) 0.66 m/sec (partially filled)

Pressure Pipe Velocity (maximum) 3 m/sec

Distribution box gates Provide to each Process Basin

Gate Materials 316 Stainless Steel

Return Activated Sludge Pumping

Return Activated Sludge Design Flow 0.25 to 1.5 x the Average Daily Flow, depending on process

Allowable Pumps

Allowable Pumps

Archimedes Screw Pumps

Solids Handling Single Vane Centrifugal Pumps with VFDs

Dry Pit Solids handling Submersible Pumps with VFDs

Waste Activated Sludge Pumps

Design Flow 2% of Treatment Plant Average Daily Flow (variable)

Allowable pumps

Dry Pit Solids Handling Submersible Pump

Solids Handling Single Vane Centrifugal Pumps with timer operation

Chemical Feed Pumps

<200 l/hr Mechanical Diaphragm Pumps

200 l/hr to 1000 l/hr Stainless Steel Progressive Cavity Pumps for polymer only

> 1000 l/hr Hose Pumps


3.4.3 Biosolids Systems Table 3—6. Biosolids System Criteria

Secondary Sludge Thickening Systems

Design Flow Minimum 2% of Plant Average Daily Flow, to be confirmed by process modeling supplemented by empirical calculations

Solids Loading Rate 3 kg/m2‐h

Acceptable Mechanisms

Center Pivot Type with Rotating Rakes and Sludge Collection Pockets (Pickett fence). Gravity Belt Thickeners prior to anaerobic digesters Similar to Huber Ros2 for plants with mixed anaerobic digesters.

Typical Sidewall Depth 3 m for pickett fence thickeners

Material 316 stainless steel mechanisms below water line

Process to Thicken 0.7% Waste Activated Sludge to maximum 3% ahead of digesters

Aerobic Digesters (EA and OD Systems) with design solids retention time less than 30 days.

Design Flow 2% of Plant Average Daily Flow

Design Solids Retention Time 40‐60 days

Aeration Coarse Bubble Air Diffusion or Line shaft surface aerators.

Allowable Mixing systems with prethickend sludge ( Pickett Fence prethickening)

Slow Speed Draft tube Mechanical (35 rpm) for circular reinforced concrete tank (with coarse bubble aeration only)

Anaerobic Sludge Digesters

Design Flow 2% of Plant Average Daily Flow or as calculated.

Design Solids Retention Time 18 days, at 35 degree operating temperature.

Anaerobic Digester Mixing Options Slow Speed Draft tube Mechanical (35 rpm) for Circular Reinforced Concrete Tank with Concrete Roof

Tangential pumped sludge mixing design for thickened sludge concentration up to 5%

Anaerobic Digester System Features

Circular Reinforced Concrete Tank

Separate stainless steel gas holding tanks. Typical gas storage 4‐8 hours.

Energy recovery using dual fuel power generators.

Excess Gas is to be Flared or used to support Power Generation


Sludge Drying Beds

Design Cycle Interval 25 days

Tankage Concrete Walls and Floors

Wall Height 1.2 m

Max Cell Size for Sludge Removal 15 m x 30 m

Design Pan Evaporation 1 m/yr or as documented for specific location for winter months

Population Based Area Estimation 0.2 m2/population equivalent served, without pre‐thickening

Belt Filter Press Systems

Material of Machine Housing ‐ 316 stainless steel

Type of Enclosure ‐ Site built building with odor control systems if located near populated areas.

3.4.4 Pumps and Piping for Treatment Plants Table 3—7. Treatment Plant Piping Criteria

Pumps and Piping For Treatment Plants

Raw sludge pumping Constant speed recessed impeller pumps. Timer control.

Secondary sludge pumping

Single vane, solids handling pumps for WAS Screw centrifugal pumps for 0.25Q to 1.5 Q RAS range of operation, Archimedes screw pumps

Digested sludge pumping Chopper pumps or rotary lobe pumps

Liquid Process Piping

Flanged Ductile Iron with cement mortar or ceramic epoxy lining for exposed and buried. PVC, HDPE, or Ductile Iron for buried piping

Solvent welded schedule 80 CPVC Piping, flanged at valves and equipment, when indoors for Corrosive Liquids including all Process Chemicals

Potable Water Pipe 316L SS or PVC for Ø < 80 mm

Ductile Iron for Ø > 80 mm

Sludge and scum system piping Glass lined ductile iron

Process Air Piping

Schedule 5S T316L stainless steel for exposed, For buried installation use Schedule 10. Valves to be SS, HP Butterfly valves for isolation. Iris valves with mass flow meters for air control valves.


Pumps and Piping For Treatment Plants

Chemical Piping Use CPVC piping, solvent welded flanged only at valves and equipment. No threaded connections permissible.

Valves on Gravity Pipelines Eccentric cast iron Plug Valve, handwheel operated

Valves on Pressure Pipelines Motor operated cast iron eccentric plug valves, check valves to be Val Matic Type

Influent Flow Measurement Magnetic flow meters or FRP Parshall Flume, Cast‐in‐Place Concrete

Meters on all Sludge Streams Magnetic Flow Meters

Pipe Supports

All pipe supports that are not concrete saddles shall be T316L stainless steel

Valve Operators Geared operators for all plug valves, hand wheels for knife gate valves, use electric actuators for 600 mm and larger valves

3.4.5 Mechanical Odor Control Systems Table 3—8 Mechanical Odor Control System Criteria

Mechanical Odor Control Systems

Treatment Plants located within 2000 m of Populated Areas will be equipped with Mechanical Odor Control Systems for the following Process Areas

Terminal Pumping Station Wetwells

Flow Distribution Chambers

Conventional Grit Chambers

Primary Clarifiers (Odor Control Dome or flat covers) for clarifiers within developed communities

Sludge Thickening and Mechanical Sludge Dewatering Units

Types of Treatment

Biological filtration with activated carbon polishing for normal loadings

Wet chemical scrubbers for anticipated extreme odor issues, as at inlet works receiving flow from long pipelines. Chemical dosing along pipelines may also be needed to control difficult odor problems.

Design Air changes

1.5 air changes per hour plus aeration volume (tanks, channels and wetwells) 12 air changes per hour continuous (rooms with open sewage tanks) 30 air changes per hour intermittent (hazardous chemical storage rooms), upon building entry.

Odor Control Systems shall be designed specifically for the constituents of the off‐gases intercepted


3.4.6 Lagoon Treatment Systems Table 3—9 Lagoon Treatment System General Guidelines

Lagoon Treatment Plants General Guidelines

Very simple advanced wastewater treatment using anaerobic and aerobic biological pond systems

Suitable for flows less than 2000 m3/day. Larger systems will be considered on a case by case basis, provided that land is available and the topography, geology, and site location is appropriate for lagoon construction and operation

Suitable for large open areas more than 1,000 m away from populated areas.

Pond systems can be very minimally mechanized for very low operation and maintenance costs. They will require a full time operation and maintenance staff for maintenance operations that resemble farming operations.

Tertiary Treatment

Lagoon Plants in Libya shall be designed to treat to a level suitable for a broad range of water reuse. In Libya either continuous flow submerged wetlands or intermittent sand filtration appropriate for providing the desired water reuse effluent quality. Other advanced treatment methods will be considered on a case by case basis.

Lagoon Treatment Plants with Maturation Ponds and or constructed tertiary wetlands will not be required to have disinfection.

Aerated lagoon plants with intermittent sand filters shall have horizontal open channel ultraviolet disinfection systems.


Table 3‐10. Aerated Lagoons Criteria

Anaerobic Lagoons followed by 2 stage aerated lagoons (AL), and settlement ponds

Anaerobic Lagoons shall not be located within 2000 meters of populated areas. Where this is not possible anaerobic lagoons shall be covered as an odor control measure.

Approximate size per 1000 m3/day capacity 10 ha including tertiary wetlands.

Flow inlet and outlet chambers shall be diagonal from each other to prevent short circuiting

Three flow channels, two mechanized, one on mechanized

3‐ coarse screens, 2‐ mechanical fine screens

Grit chambers: 2 rectangular traveling bridge type aerated grit chambers with coarse bubble air diffusers and grease removal. Ancillary systems include cyclone separator and grit classifier, conveyor and 2‐500 liter grit storage bins

Anaerobic Lagoon Earthwork

Aspect Ratio 2:1

Excavation and embankment slopes 4:1

Pond depth 4 ‐ 5 m

Detention time 4‐5 days

Lining 150 mm concrete wearing surface panels over 60 mil thick HDPE (high density polyethylene)

Aerated Lagoons

Stage 1 Aerated Lagoon – Complete Mix with air transfer sized for complete oxidation of influent biochemical oxygen demand and Ammonia (NH4). Five day hydraulic residence time. Stage 2 Aerated Lagoon – 50% complete mix. Primary role will be nitrification and partial denitrification. Eight day hydraulic residence time Stage 3 Final settling of suspended solids. Two day hydraulic residence time. Final settlement Pond ‐ Depth 4‐5 meters.

Aeration Equipment Floating, cable stayed slow speed line shaft surface aeration One spare aerator for each 3 duty aerators

Aerated Lagoon Lining 1.5 mm HDPE (high density polyethylene) extended and anchored in top of embankments.

Aerated Lagoon Earthwork

Aspect Ratio 2:1 Minimum Number of lagoon trains 2 Excavation and embankment slopes 4:1 Minimum water depth 4.0 meters Freeboard 0.8‐1.0 meters


Table 3—11 Facultative Lagoon Treatment System Criteria

Anaerobic Lagoon followed by Stabilization Ponds (SP) and Maturation Ponds

Approximate site area requirement 20 ha per 1000 m3/day

MINIMAL ENERGY AND MINIMUM MAINTENANCE REQUIREMENTS

Screening and grit removal

Fixed 25 mm manually cleaned bar rack followed by manually cleaned grit chamber

Flow Distribution Chambers will be arranged with inlet and outlet boxes diagonal from each other (AL) (SP)

Manual Grit Chambers (SP)velocity controlled at 0.4 m/sec Aerated Grit Chambers (AL)

Nominal Hydraulic Detention Time 5 days (AL) (SP)

Basin interior and exterior slopes 4:1 (AL) (SP)

Anaerobic Lagoons provide primary treatment, with an estimated 50% removal efficiency for BOD5 and TSS similar to the previously presented Aerated Lagoon system

Minimum number 2 for all Pond Treatment Systems (minimum 2 process trains)

Stabilization Ponds. Also called Facultative Ponds. These ponds are oxygenated by algal photosynthesis.

Minimum number of lagoons 2 in series per process train Slopes of excavation and embankments 4:1 Design water depth 1.5 meters with 0.8‐1.0 meter freeboard 1.5 mm thick high density polyethylene liner Stabilization pond design hydraulic residence time for Libya 15 days Inlet and outlet boxes to be diagonal from each other for all pond systems, to reduce short circuiting in the lagoons.

Maturation Ponds (To provide additional solar based oxidation and reduction of Coliform related bacteria, with some denitrification)

Design water depth 1.5 meter Design Hydraulic Residence Time 15 days HRT Design water depth 1 meter Slope of excavation and embankment 4:1 Aspect Ratio 2:1 Lining 1.5 mm thick HDPE (high density polyethylene) Minimum number of maturation ponds 2 in series per process train


3.4.7 Tertiary Treatment for Lagoons Table 3—12 Tertiary Treatment Criteria

Tertiary Wetlands

Tertiary Wetlands shall be of the submerged flow‐though Wetlands Type designed for the removal of all nitrogen and phosphorus remaining in Lagoon treatment plant effluent. Effluent from the wetlands can be piped to a earthen treated water reservoir equal in size to one day’s plant average design flow that will be used for water reuse purposes

Hydraulic Flow Distribution. This will be using at‐grade level distribution channel with overflow rectangular weirs placed at 4 meter intervals. Stop logs will be used to block off selected weirs to facilitate uniform flow distribution.

Wetlands plants shall be aquatic plants and grasses that are indigenous to the general location of the treatment plant

Underlying gravel shall be 10 mm gravel, one meter deep.

Lining beneath gravel shall be 60 mil thick HDPE (optional)

Minimum number of wetlands cells: 2

Intermittent Sand Filtration

Intermittent Sand Filtration will be designed to filter out residual suspended solids and to reduce the remaining nitrogen in lagoon effluents.

Hydraulic Flow Distribution. Duplex pump systems shall be used to pump the flow to alternating pairs of sand filters. Filters shall be sized in accordance with published guidelines or 0.1 m3/m2‐day, which equates to 1 hectare filter area for 1,000 m3/d flow.

Dimensional Information

Intermittent Sand Filters shall be constructed with vertical concrete walls and bottom concrete slab. 0.25 – 0.35 mm Sand shall have a depth of 1.1 meters and shall be placed over 0.33 meters of 4 mm gravel. Effluent shall drain thru slotted pipes laid at the base of the gravel material.

Aspect Ratio is 2:1 Minimum Number of Filters: 2 in parallel

General Requirements Pertaining to entire operating projects

All treatment channels and basins will be reinforced concrete

Minimum velocities at low flow in channels will be 0.8 m/sec

For long sewage pumping pipelines, a means of oxidation of the sewage to prevent odors shall be considered in the design All concrete structures will have corrosion resistant coatings extending from 0.3 meters below the water line to the top of the basin walls


3.4.8 Package Treatment Plant

1. Small Package Sewage Treatment Plants shall be pre‐engineered. The treatment plant manufacturers and equipment suppliers shall have at least 10 years experience in the design and construction of package sewage treatment plants and the specific treatment plants offered shall have at least 5 years of acceptable performance in the field. The plants are intended for permanent use.

2. The wastewater treatment process shall consist of a headworks facility suitable for the proposed process, followed by extended aeration activated sludge with an SRT of at least 30 days at design loadings. The treatment process types may be conventional extended aeration or an equivalent process technology using Activated Moving Bed (AMB) Biomedia, Fixed Activated Sludge Treatment (FAST), or Membrane Bioreactor (MBR). With exception of the MBR plants, all small package treatment plants shall include tertiary filtration by disk filters, or equivalent.

All plant types shall have UV disinfection and chlorine dosing for residual. For all plant types, the treatment process performance shall be equivalent to a conventional extended aeration plant and capable of producing a stabilized waste sludge at the stipulated loadings. Aerobic sludge digestion may be included for a lower SRT plant as an alternative to achieving the desired sludge stabilization results. All treatment plant types shall achieve full nitrification and substantial denitrification, as indicated by the effluent standards to be met.

3.4.9 Mobile Package Treatment Plant

1. Small and mobile package Sewage Treatment Plants shall be pre‐engineered. The treatment plant manufacturers shall have at least 10 years experience in the design and construction of package sewage treatment plants and the specific treatment plants offered shall have at least 5 years of acceptable performance in the field. Tankage shall be high quality structural steel with the best available coatings for corrosion protection. Sacrificial anodes shall be supplied with every steel tank or structure. The plants are intended for temporary use while permanent facilities are under construction. When no longer needed, the plants are intended to be relocated by others either to storage or to another location in need of a temporary treatment plant.

2. The wastewater treatment process shall consist of a headworks facility suitable for the proposed process, followed by activated sludge using Activated Moving Bed (AMB) Biomedia, Fixed Activated Sludge Treatment (FAST), or Membrane Bioreactor (MBR). The FAST and AMB Biomedia treatment plants shall include tertiary filtration by disk filters, or equivalent. All plant types shall have UV disinfection and chlorine dosing for residual. The treatment process reactors shall have an F:M ratio (Food to Microorganism ratio) equivalent to an extended aeration plant and minimum SRT of 20 days, capable of producing a stabilized waste sludge at the stipulated loadings.

JUNE 2009 REVISION NO. 02 STORM Water 4‐1

4 Storm Water HIB has developed design criteria for storm water drainage systems for use in their projects. The criteria are presented to support the design intent of the HIB infrastructure. The intent of this section is to provide design criteria for storm water only, free from sewage or other wastewaters. It is understood that certain situations may require deviation from the criteria presented herein and under this circumstance approval of the proposed criteria from HIB is required.

Since rainfall events in Libya are relatively infrequent, the design engineer should evaluate the best storm management approach based on the information provided in this document to achieve a balance between construction cost and an acceptable level of performance.

4.1 Storm Water Management Policy Management of storm water is governed by Libyan Laws; two of the most pertinent articles from the Libyan Law No. (15) of 1370 PD (2003) for Protecting and Improvement of the Environment are as follows:

Article (34) prohibits discharge of polluted water to the sea. The Article reads:

“It is prohibited to discharge polluted water into the sea directly through drainage pipes, whether the drainage is on the coast or therefrom or through canals or sewers, including internal gravity flow water courses before treatment thereof as per the effective legislations and regulation issued for implementing.”

Article (43) reads:

“The domestic and industrial drainage water is considered as a water sources and shall not be wasted or disposed of after treatment thereof, unless it is proved that its use is impractical. Then, it shall be disposed of under the rules and regulations issued without causing any environmental pollution.”

In general, Libya receives little rainfall, most of the rainfall occurs in coastal areas. The average annual total rainfall along the Mediterranean Coast ranges from 559 mm at Shahat in the eastern coast line to 238 mm at Zuara close to the Tunisian boarder. South of 300 N Libya is almost desert with annual total rainfall ranging from 20 mm at El Kutra to 9 mm in Sebha.

The Housing and Infrastructure Board (HIB) is building infrastructure throughout the country. The infrastructures consist of housing, roads, and facilities for water distribution and treatment, for wastewater collections and treatment, and for storm water collection. As development progresses the land use of the area changes, increasing the impervious surface that do not readily absorb rainfall runoff. Therefore, sound and practical storm water management practices must be implemented to effectively utilize the precious resource ‐ water.


4.1.1 Storm Water Quantity Management As part of formulating a comprehensive Storm Water Management Policy, HIB has developed background information and criteria and best management practices for storm water quality enhancement. The storm water management objective is to eliminate or minimize discharge of storm water runoff from the design storm to the Mediterranean Sea. Where this is not achievable HIB should be consulted in advance and the project will be reviewed on case‐by‐case basis. As a general guide line the options presented below should be taken into consideration. The items listed below are tools‐in‐a‐tool‐box and should be regarded as a general guidance and applied on a case‐by‐case basis for a particular site.

• Where topographic conditions of the site and project conditions allow, rain water should be collected from roof tops into underground or ground level cisterns for onsite landscape irrigation. The storage cisterns should be adequately sized based on the rainfall information and amount of roof top area. Basic information such as runoff coefficient for various land use can found in the in Section 4.2.

• Storm water runoff from paved surfaces such as parking lots could be directed to sheet flow to nearby landscaping areas or collected and stored during the rainy season for landscape irrigation in the summer months. Runoff from the parking area may be contaminated and requires per‐treatment to remove sediment, sand, trash, and other pollutants that are washed away from the paved surfaces. The treatment envisioned should be simple and effective technique that reduces trash and sediment that could be trapped or removed with extended detention.

• Storm water runoff could be collected from the road ways through collector pipes and stored and used for landscape irrigation at the appropriate locations after pre‐treatment. Guidance for sizing methodology of storm water collectors and conveyance system including rain‐fall intensity duration curve for several location in Libya is included in this document.

• Storm water could be collected from the impervious surfaces and allowed to infiltrate into the ground to recharge the ground water. Guidance for sizing methodology is included in this document.

4.1.2 Enhancing Storm Water Quality Storm water from paved surfaces such as roads is contaminated with various pollutants such as trash, sediment, oil and grease, bacteria and other pollutant as a result of human activity. Some degree of treatment is required depending on the reuse objectives and receiving outfall such as ecologically sensitive areas. The quality of storm water can be greatly improved by utilizing simple but effective treatment technologies. Most of the pollutants in storm water runoff can be trapped at the source before reaching the storm water collection and conveyance system. For pollutants that cannot be trapped at the source, the storm water runoff could be collected and detained at strategic locations to remove pollutant by gravity settling. When further enhancement is desired, the storm water runoff is directed into a treatment system further enhancement.


The activity of enhancing the quality of storm water is generally referred as Best Management Practice. Best Management Practices could be:

• Non‐structural and • Structural measures

Non‐structural measures include street sweeping, public education such as anti‐litter campaign and proper disposal of solid waste or trash. Non‐structural measures could be very effective in reducing gross pollutants such as plastics which do not bio‐degrade. Proper and strategically placed signs and billboards could be very effective methods of public educations. Structural measures require construction of structures such as oil‐and‐water separators, detention basin, filter strips, grass swales, and infiltration tranche and basin. The above mentioned practices should be evaluated on a case‐by‐case basis for applicability in the particular project site.

4.2 Storm Water Design Criteria Storm water facilities design must be compatible with the appropriate storm water discharge and disposal options. For example, it must be determined if the storm water will be collected and removed from the site or if it will be retained on site and allowed to infiltrate into the ground and/or evaporate. In general, Libya has a dry climate. Rainfalls in Libya are intense, short in duration, and infrequent. Along the Mediterranean coast, the wettest months are from September to March. For example, the average annual total rainfall in Tripoli is approximately 230 mm based on 40 years data recorded at Tripoli International Airport. The maximum annual total rainfall in Tripoli during the same period was 560 mm recorded in 1982 and with a minimum annual total of 52 mm recorded in 1999. Other areas in the country have significantly different rainfall records. Thus, the approach to storm water drainage design must consider the local rainfall records for determining the appropriate design storm.

4.2.1 Design Storm Design rain storms are typically determined based on long term rainfall records to develop values for various recurrence intervals. For local drainage facilities such as subdivision collector roads, a storm with a 5‐year recurrence interval shall be used for calculating storm water runoff and sizing drainage collectors and mains. For major drainage facilities, a 50‐year storm event shall be used for calculating storm water runoff and sizing the major drainage facilities. Major drainage facilities are large facilities that receive inflows from multiple local drainage areas. Major drainage may also be critical drainage areas, such as airports or underpasses, where localized flooding is unacceptable. A 25‐year design storm shall be used for sizing the collection system for freeway or major roads such as the Ring Roads.

This section provides the design storm for sizing drainage facilities for different locations in Libya. However, if the design storm is not available for a particular project location, the designer is responsible for collecting and evaluating the available rainfall data and calculating the intensity‐duration of the design storm appropriate for the project location. The proposed design storm intensity and duration shall be reviewed and approved by HIB before any detailed designs are undertaken. Copies of all rainfall data used for determining the design storm shall be submitted together with the calculated design storm intensity‐duration for the design frequency.

Table 4—1 presents rainfall intensity‐duration for the various frequencies for the City of Tripoli and Figure 4‐1 presents the same information in a graphic form for 5 and 50 year recurrence intervals based


on the values in Table 4—1. Similar figures could be constructed for other frequencies if desired from the values presented in Table 4—1.

Table 4—1: Intensity‐Duration Table for Various Frequencies for Tripoli, Libya

Time, Minutes Intensity, mm/hr

2‐year 5‐year 10‐year 25‐year 50‐year 100‐year

5 94.8 116.5 134.6 147.0 158.7 165.7

10 57.9 73.7 85.8 95.0 104.0 109.3

15 43.4 56.4 65.9 73.6 81.2 85.7

30 26.6 35.7 42.0 47.5 53.2 56.5

60 16.2 22.6 26.8 30.7 34.8 37.3

90 12.2 17.3 20.6 23.8 27.2 29.2

120 9.9 14.3 17.1 19.8 22.8 24.6

180 7.4 10.9 13.1 15.4 17.8 19.3

360 4.5 6.9 8.4 9.9 11.7 12.7

720 2.8 4.4 5.3 6.4 7.7 8.4

1440 1.7 2.8 3.4 4.1 5.0 5.5

Figure 4‐1: Intensity Duration Curve for Tripoli, Libya

0

20

40

60

80

100

120

140

160

180

5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90

Inte

nsity

mm

/hr

Time, Minutes

50‐Year

5‐Year

i 50= 423.5* t(‐0.61)

i 5= 336.9* t(‐0.66)


Table 4—2: Runoff Coefficient Values

Area Description Runoff Coefficient, C

Categorized by Surface

Asphalt 0.7 to 0.95

Brick 0.7 to 0.85

Concrete 0.8 to 0.95

Sandy Soil 0.05 to 0.2

Clayey Soil 0.13 to 0.35

Categorized by use

Administration 0.5 to 0.75

Educational 0.6 to 0.8

Shopping Center 0.6 to 0.8

Medical Facilities 0.6 to 0.8

Religious and Cultural Facilities 0.7 to 0.8

Agricultural 0.3 to 0.5

Unimproved 0.1 to 0.3

Parks and Playgrounds, unpaved 0.1 to 0.25

Playground, unpaved 0.2 to 0.35

Business Districts 0.7 to 0.95

Residential

Small villas (<2500m2) 0.3 to 0.5

Large villas (>2500 m2) 0.25 to 0.4

Apartments 0.65 to 0.85

Industrial

Light 0.5 to 0.8

Heavy 0.6 to 0.8


4.2.2 Runoff Coefficients Runoff for the design storm event shall be calculated based on the Rational Method, whereby the runoff flow, Q, equals a coefficient, C, times storm intensity, i, times the catchment area, A.

Where:

i ‐ Rainfall intensity, m/sec C – Runoff coefficient (dimensionless) A – Drainage area, m2 Q – Flow, m3/sec Rainfall intensity‐duration for other locations and additional information with sample calculations is included in Attachment 4‐1 at the end of Section‐4. Runoff coefficients based on ground surface type and land use are provided in Table 4—2: Runoff Coefficient Values and shall be used for design runoff flow calculations. Composite runoff coefficients in each catchment can be determined by multiplying specific land use areas by their respective coefficients and dividing the sum of these products by the total drainage area.

4.2.3 Runoff Volumes Runoff volumes are calculated based on individual catchment areas, catchment characteristics and the design storm(s). The equation for runoff flow volume for any given catchment is shown below:

Where:

V is the runoff volume (m3) C is the runoff coefficient (dimensionless) d is the total storm depth (m) A is the catchment area (m2)

Design flow rates are based on clearing the runoff volume within the required clear time after the end of the storm event without exceeding the maximum allowable depth of localized flooding. Based on hydraulic analyses, in locations where localized ponding does not exceed the maximum allowable depth and with the required clear time, an average design flow may be used for sizing the drainage conveyance and pumping stations. The average flow rate is determined by the following relationship:

.

Where:

Qavg average runoff flow rate (l/s) V runoff volume (m3) ts storm duration (hours) ct clear time (hours)


Where possible, sizing collection networks based on an average runoff rate can reduce the overall size and cost of the collection system. Some facilities, such as roadway underpasses, require a zero clear time. In such cases, the maximum peak flows should be accommodated by the drainage piping and pumps.

4.3 Hydraulic analyses Hydraulic analyses shall be carried out using the Manning’s formula (a sample calculation is included in Attachment 4‐1 at the end of Section 4) or approved computer modeling software. Acceptable models are Infoworks, SewerCAD, Mouse Model, InfoSewer, and SWWM. Other equivalent commercially available models may be used with prior written approval by HIB.

Roughness coefficients based on the pipe material as shown in Table 4—3 shall be used. The roughness coefficient is a measure of the friction resistance to flow by the interior surface of the pipe. The roughness therefore is a function of the pipe material, age, and condition. Poor pipe conditions are to be assumed for system designs. However, pumping facilities shall be designed to operate satisfactorily for either normal or poor conditions.

4.3.1 Flow Velocities The minimum design velocity allowed through drainage conduits (to prevent excessive settling of solids) and the maximum flow allowed, to avoid abrasion of the gravity conduits, are as shown in Table 4‐4.

Table 4—3: Typical Roughness Coefficients

Table 4—4: Minimum & Maximum Velocities

Pipe Description Minimum Velocity

(m/s) Maximum Velocity

(m/s)

Gravity pipe 0.6 3.0

Pressure pipe 1.0 2.0

In situations where the minimum design velocity cannot be achieved for gravity pipe, the distance between manholes should be reduced to better accommodate more frequent cleaning.

Pipe Material

Manning’s, n

Normal Maximum

uPVC 0.010 0.013

GRP 0.010 0.013

HDPE 0.010 0.018

RCP 0.012 0.016


4.3.2 Clear Times Allowable clear times have been established for the different types of areas where new storm water drainage may be required. These times refer to the period of time after the end of a storm event during which limited water ponding is permitted. Table 4—5 identify the clear time for each of the main service areas. The maximum allowable depth of ponding along the roadway with curb and gutter is the height of a road curb which is 150 mm.

Table 4—5: Allowable Clear Times

Area Designation Clear Time, hours Comments

Freeways/Expressways 0 See Note 1

Arterial Roads 0 See Note 1

Collector Roads 1

Local Roads 1

Roadway Underpasses 0 See Note 1

Parking Lots 3

Airport Runways 0 See Note 1

Airport Taxiways 0 See Note 1

Airport Infield 24 See Note 2

Notes:

1. Water shall be cleared within the time frame of the storm, and flooding during the storm will be minimized to avoid unnecessary disruption of traffic.

2. Shorter clear times shall be sought where possible.

4.3.3 Depth of Flow The design depth of flow for all drainage pipes is assumed to be full, and when surcharged the energy grade line should not be higher than the natural ground surface. The system may be designed to operate under surcharge flow conditions for most pipes in order to achieve the required clear times.

4.4 Pipe Materials Drainage pipe materials have been selected to be consistent with local standard practices, based on economics and local availability. Table 4—6 lists allowable pipe materials for various pipe sizes.


Table 4—6: Allowable Pipe Materials

Pipe Material Diameter (mm)

uPVC, HDPE 200 to 600

GRP, RCP 300 to 1400

RCP Greater than 1400

The minimum pipe diameter permitted for drainage system gravity collection pipes is 300 mm. Land subdrains under detention ponds and infiltration areas can be 200 mm in diameter. Connections to street gutters and other inlets may also be 200 mm diameter, and shall have a slope of 2 percent or greater.

RCP pipe shall be provided with protection from sulfide corrosion, such as PVC or GRP lining or possibly a sacrificial lining of mortar with calcareous (limestone) aggregate.

4.4.1 Pipe Gradients Minimum gradients are determined based on minimum scour velocity requirements. Larger pipe diameter gradients are based on constructability as well as minimum velocity requirements. Recommended minimum gradients are listed in Table 4—7. The minimum gradient considered technically achievable during construction is 0.00050 m/m.

Table 4—7: Minimum Pipe Gradients

Pipe Diameter Minimum Gradient/

250 0.00246

300 0.00190

400 0.00132

500 0.00098

600 0.00077

700 0.00063

800 0.00053

900 0.00050

1000 0.00050

larger than 1000 0.00050


4.4.2 Minimum Cover Requirements For gravity pipes, the minimum recommended cover in order to protect from external loads is 1.2 m above the pipe crown. For pressure pipes, minimum cover is 0.8 m in unpaved areas with no vehicular traffic and 1.0 m in paved areas with vehicular traffic. If the available cover is less than specified, then additional protection such as full concrete encasement or the use of concrete protection slabs may be required

The actual cover required for construction and access may be greater than that required solely for structural integrity. For example, the minimum cover required by the physical dimensions of a typical access manhole is 2 m above the pipe crown. However, for small pipes less than or equal to 300 mm in diameter, the required cover may be less than 1.2 m. In such cases, if inspection chambers are installed rather than manholes, 1.0 m of cover may suffice.

The maximum cover depth recommended is approximately 10 m. This maximum depth is consistent with typical pipe installation standards and manufacturer recommendations. Should the actual cover be greater than 10 m, pipe material selection should be evaluated and a higher strength class of pipe utilized.

For pipes installed less than the recommended minimum or more than maximum depths, concrete encasement may be required to protect the pipe from damage or collapse. Alternatives of different pipe size at a different slope should be considered before designing pipelines for installation outside of the specified depth ranges.

In all cases, the pipe minimum and maximum depths shall be in conformance with the pipe manufacturers’ recommendations.

4.4.3 Manholes Manholes are used to provide access to drainage lines. They shall be provided at each change in direction (vertical or horizontal) and connection of two or more lines. Manholes are to be placed at least every 100 m or the limit of existing pipe cleaning equipment, whichever is smaller. In particular, manholes should also be installed where necessary to facilitate cleaning and access. For pipe diameters larger than 1500 mm where man entry is reasonably accommodated, maximum manhole spacing may be increased to 200 m.

The manhole structures are normally circular in shape, with a minimum diameter of 1,000 mm. Manholes shall be constructed of reinforced concrete with GRP or other corrosion proof lining with prior written approval from HIB. Details of access and construction shall be in accordance with established HIB or other equivalent standards and details.

Manholes on gravity pipes shall be provided at any changes in horizontal direction and where pipe sizes change. For transitions between pipes of different diameters, typical design is to match the crown elevations of the pipes. In the event that this is not possible, the invert of the larger sewer pipe can be raised to match the 0.8‐depth point of both sewer pipes.

4.4.4 Connection Chambers Special connection chambers shall be used in locations where manholes are not sufficient for the required connection. This is most commonly the case where multiple large pipes must be connected to


equilibrate flows and/or flow control is to be implemented. Flow control shall be provided through the use of penstocks.

4.4.5 Catch Basins and Trench Drains Approved catch basins, trench drains, and gullies shall be used throughout the drainage projects. Cast iron inlet grates shall be used throughout. Maximum spacing of catch basins in any major or subdivision road shall be 25 m unless it is demonstrated by project specific calculations a wider spacing is justified. Flush‐mounted inlet structures may be used in areas without curbing.

Trench drains are required where sheet flow is likely, or where traffic loading is expected to exceed standard highway loads. Standard details for trench drains shall be used throughout.

Inlets and gullies shall be provided with sediment traps with access for maintenance cleaning.

Inlet covers shall be provided with a sand trap to prevent accumulation of sand in curb inlet catch basins.

4.4.6 Utility Crossings Utility crossings for storm drains are to be consistent with internationally accepted standards, as shown in Table 4—8.

Table 4—8: Utility Crossing for Storm Drains


Vertical Clearance 30 cm (if less than 30 cm, use concrete saddle) Carry encasement to first joint on each side of crossing

Horizontal Clearance 3.0 m; if in same trench, place other utility on separate bench on undisturbed soil above drainage line

Potable Water Lines Always place above drainage lines

4.5 Detention Ponds (Separate Storm Drainage Only) Storm water detention facilities, such as ponds, dry basins and underground chambers, can be effective methods to attenuate peak flows by slowly releasing runoff volumes, and to improve water quality by allowing pollutants to settle. Attenuating peak flows offer the benefit of reducing the downstream pipe size and cost of construction of storm water management systems. Improving water quality reduces the risk of collection systems becoming blocked or plugged with sediments and debris, and the risk of releasing pollutants to the environment.

The ponds are typically located in areas that are at the naturally occurring lower elevations in the catchment areas, with a minimum of one pond per catchment area. There are two types of storm water detention basins: dry and wet. Dry detention basins are designed to be normally dry and become temporarily inundated after a storm event. Dry detention ponds may be used for recreational activities, such as soccer fields or the like, for all times except where there is a major rainfall event.


Wet detention ponds are designed to have a permanent pool at all times. In addition to runoff calculation determining of evaporation rate should be performed to ensure there is a permanent pool of water at the desired depth. Properly sized, designed, and maintained wet ponds also add an amenity feature to the surrounding areas. Careful consideration should be given to provide a minimum depth sufficient to avoid creating a mud pit. In some instance a supplemental water source such as ground water or treated water may be needed. In areas of high groundwater, the construction of detention ponds should be avoided.

The storm water detention facilities shall be designed to safely contain and slowly release runoff volume from a 50‐year, 24‐hour rainfall event in order to accommodate a larger storm depth. It is assumed that during the 50‐year storm event, 15 percent of the total runoff is discharged from detention facilities before water levels reach peak stage. Therefore, the detention facility is sized to store a runoff volume equal to 85 percent of the total runoff volume from the 50‐year, 24‐hour rainfall event.

4.5.1 Pond Inlet and Outlet Structures Where the storm water collection system is discharged to ponds, side slopes are to be protected from erosion with stone pitching or rip‐rap. Where inflow velocities exceed 1.5 m/s, an energy dissipation structure should be provided. Outlet structures should be sized adequately to empty the flow at the desired time period. Discharge control structures shall be designed to release total runoff from the 5‐year 24‐hour rainfall event over a period of 48 hours and to release the total runoff from the 50‐year 24‐hour rainfall event over a period of 72 hours. The outlet structures could be weir, orifice, or other overflow structures.

4.5.2 Discharge Control Structures Discharge control structures serve two purposes:

1. To maintain surface water or groundwater levels and

2. To release rainfall runoff at an attenuated peak discharge rate.

Discharge control structures are an integral part of a passive storm water management system. They are used to maintain surface water levels and groundwater levels in detention ponds at target elevations. The target elevation is typically set at not lower than the natural, pre‐construction wet season groundwater elevation. However, other factors may also be considered when selecting a target elevation. The target elevation becomes the design control elevation. Each storm water pond shall be assigned a design control elevation based on the best available groundwater data for that specific location.

Discharge control structures shall be sized to release runoff from certain design storms over a specified number of days without allowing the pond water surface levels to exceed the maximum design high water levels. Discharge control structures release stored runoff through either an over flow weir, or a circular orifice, or a combination of the two. Rectangular weirs and orifices shall be designed using conventional formulas.

4.5.3 Pond Depth The depth of water in a detention pond is an important consideration during design. While it is possible and often desirable to minimize the land area required for a detention pond by increasing its depth, the result may create conditions that can be hazardous. The depth influences both the safety of operation


and the quality of effluent from the pond. Pond side slopes generally should have a stable slope with a gradient of 1 vertical to 5 horizontal (1V:5H). This gentle gradient allows vehicle access for maintenance of the side slope and bottom. It also allows easy access for the possible recreational use of the pond during dry months. During design, it may be desirable to adjust the side slopes for aesthetic reasons. Pond side slope options include natural slope (1V:5H), hardened slope terraced, and vertical retaining walls.

For wet ponds, the recommended pool of water should be a minimum of 1.5 meters at the deepest location. The submerged side slope of the permanent pool could be increased to 3H:1V once the depth in the permanent pool is greater than 0.5 meters. When site condition does not allow the above recommendations, other values could be used with prior written approval from HIB.

4.5.4 Detention Pond Emptying Efficient and complete clearing of dry detention ponds after a storm event is essential. Shallow, stagnant pools promote breeding of nuisance insects. Deeper, wet ponds will develop plants and may attract birds and other wildlife. Wet ponds may act as water features especially when associated with pocket parks or other public use areas.

4.5.5 Dry Detention Ponds The following should be considered in sizing of all dry detention ponds:

3. Size area to detain runoff volume from the design rainfall event plus 0.3 m of freeboard

4. Provide 5:1 side slopes or stable side slope as dictated by soil conditions

5. Grade pond bottoms to central points to accumulate flows to central collection points. A slope of two percent may be considered.

6. Pond bottoms shall be at least 5 m above the average groundwater level.

7. Provide perimeter land drain system to stabilize side slopes where groundwater levels are expected to be higher elevation than the pond control elevation.

4.5.6 Wet Detention Ponds The following should be incorporated in all wet detention ponds:

1. Size area to detain runoff volume from the design storm plus 0.3 m of freeboard.

2. Provide 5:1 side slopes or stable side slope as dictated by soil conditions.

3. Pond bottom shall be at least 1.5 m below discharge control elevation.

4. Consideration should be given to provide supplemental aeration and mixing within the pond to enhance water quality.

5. Provide perimeter land drain system to stabilize side slopes where groundwater levels are expected to be higher elevation than the pond control elevation.


6. Provide a gently sloping littoral shelf with aquatic vegetation along the wetted perimeter of the pond for aesthetics and safety.

4.5.7 Retention Ponds Retention ponds are intended to retain and impound all flow from twice the average annual rainfall without overflow. They shall incorporate the following:

1. Size volume to contain runoff from rainfall equal to two times the annual average rainfall.

2. Outlet via infiltration to groundwater, evaporation, or beneficial reuse such as landscape irrigation.

3. The depth is determined by inlet pipe levels.

4.5.8 Buried Detention Chambers Where appropriate, consideration should be given to the use of buried detention chambers. These chambers usually comprised of interconnected elements of perforated pipes or structures in a gravel envelope.

1. Size area required for detention chambers to detain runoff from the design storm based on the estimated storage capacity for each chamber and gravel envelope.

2. Provide oil‐water separators at all inlets into the chambers

3. Estimate pond areas assuming 0.66 m3 of storage per square meter of land area.

This method of storm water detention is only effective where the chambers are consistently above the groundwater table with a positive outflow available at all times. The buried chambers will act as land drains and keep the groundwater level below the chamber inlet.

Buried detention chambers are to be located using the same horizontal offset criteria as used for storm water management basins within an Airport.

4.6 OilWater Separators Because rainfall events are infrequent, the first flush of storm water runoff from urbanized areas typically contains a relatively high pollutant load. Oil‐water separators may be required to reduce the discharge of pollutants to the environment by capturing settling solids and floatable oils and grease. Where required, oil‐water separator designs shall meet the following requirements:

1. Shall be constructed of impermeable materials and with minimum of three chambers in series with access manholes into each chamber.

2. For large catchment areas, provide a by‐pass channel shall be provided to prevent overflow of oil or contaminants as a result of heavy downpours.

3. Provide a volume capacity from an average one‐hour storm.


4. A metal grill or appropriately designed screen shall be provided to prevent debris from entering the oil‐water separator.

5. Separator discharge shall meet the following water quality criteria:

(a) No visible oil and grease.

(b) Suspended solids less than 50 mg/l during dry weather flow.

(c) Suspended solids less than 100 mg/l during wet weather flow.

(d) Maximum horizontal design velocity is 0.3 meters per second.

6. For large catchment areas, size the separator to treat storm water runoff from the “first flush.”

7. Design depth of Separator shall be a minimum of 1.22 m and maximum of 2.44 m per WEF MOP FD‐3, “Pretreatment of Industrial Waste,” 1994.

8. Provide access for regular maintenance to inspect units and remove accumulated oils and settled solids.

9. Depth‐to‐width ratio equal to 0.3 minimum and maximum 0.5 per WEF MOP FD‐3, “Pretreatment of Industrial Waste,” 1994.

10. Velocity shall be based on the sustained peak storm water discharge rate from the 5‐year storm event.

11. Flow in excess of runoff from 5‐year storm event shall be bypassed around the separator after coarse screening.

12. Maximum width of a single Separator should be 10 m for reasonable constructability.

13. Captured oil film and floatable solids in separator to be displaced into trough collection system having weir crest elevation equals calculated High Water Level in Separator plus 0.15 m.

14. Sediment collected in Separator to be directed to sump for pumping to truck loading station.

15. Separator provided with inlet coarse screens consisting of in‐channel manual bar racks having 50 mm spacing between bars. Bar racks are to be vertical and have full width depressed floor trench 0.4 m depth upstream of bar racks having overhead hatch for vertical lift of debris from trench.

16. Provide one sump pit with recessed channels in the bottom slab and one lift‐out submersible sump pump for dewatering each Separator cell.


17. Provide one 100 mm diameter water supply line, from pond dewatering pump station or other available water supply, into each parallel Separator for displacement of waste floatable materials.

18. Accumulated floatable waste and oils will be displaced through a weir opening discharging into trough system to direct wastes to a sump. Sump pump shall discharge to a truck filling station with spill containment and piping shall be fitted with either disconnect couplings at grade or with an overhead tanker filling arrangement.

19. For larger units, provide a one‐ton jib crane for removal of screen, screenings, and grit. Provide removable, motorized, one‐ton wire rope hoist for use on the jib crane.

20. For large oil‐water separators, provide electric actuated sluice gates at the inlet and outlet from the separator to isolate the units for maintenance and repairs.

4.7 Storm water Management within an Airport It may be desirable to route storm water runoff to shallow basins located in the areas of land between runways and taxiways as part of a collection system. The basins shall have minimum horizontal offsets from runways and taxiways in compliance with FAA regulations which specify offsets distances to any changes in grade as follows:

1. Minimum offset 23 m from edge of runway pavement.

2. Minimum offset 110 m from centerline of taxiway.

3. Minimum offset 20 m from end of blast pavement for taxiways.

4. Maximum depth of basin 1.5 m

Maximum basin side slopes shall be 5H:1V. All runoff to the basins will flow freely into the collection system. The basins are not intended to detain water for any period of time after the storm event. (Reference is made to the following documents: Dubai Civil Aviation Report TD 75 – Storm water Master Plan for Dubai International Airport and the U.S. Federal Aviation Administration Advisory Circular No. 150/5320‐5B – Airport Drainage.)

4.7.1 Bird Scare For airports, bird control is a major priority for safe operation of the airport as birds are attracted to standing pools of water such as detention ponds. Provisions to keep storm water detention ponds a sufficient distance from airplane movements must be incorporated into the design. As such, no storm water detention ponds will be located within an airport or within an airport fly zone.


4.8 Groundwater Dewatering During construction continuous dewatering may be needed where ground water level is higher and this section is included to provide guidance in dewatering. Possible groundwater rise due to future irrigation and water supply system leakage must also be taken into account.

Dewatering time below the water table can be calculated using the following equation:

Where: t = dewatering time, days

A = pond area, m2

Q’ = groundwater discharge to pond per unit drawdown (to be obtained from groundwater analysis or model), m3/day/m

QP = pumped flow, m3/day

ZGW = groundwater table elevation, m

ZP0 = initial pond water surface elevation, m

ZP = pond bottom elevation, m

Groundwater levels can be lowered by using active pumping and/or passive collection from the outfall structures. The groundwater collected shall be disposed of in the storm water collection system or pumped to Treated Sewage Effluent (TSE) storage tanks, if available and mixed with the TSE for use as irrigation water. The extent to which groundwater can be blended with TSE must be evaluated on a case‐by‐case basis.

4.9 Pumping Stations and Rising Mains Storm water pumping stations are required when drainage collection network depths exceed the practical or economic constructability limit. The first preference is to use gravity drainage systems; however, due to topography and potential land use conflicts, there is the potential that some pumping stations may be needed. Pumping stations may also be required where land drain systems are employed and connections to gravity storm drainage systems are not possible.

4.9.1 Pumping Station Type The design philosophy is to maximize gravity flow and only use pumping where absolutely necessary. Most storm water pumping stations shall be submersible pump type stations. Submersible pump stations are well suited to drainage pumping given their low profile and low maintenance requirements. Pumping stations shall be sized for the storm water flows but will also be used to maintain the groundwater table below the desired elevation throughout the year.

For very large flows, storm water pumps may require use of low‐head, high‐volume axial flow pumps, or possibly screw pumps where the required head is just a lift into a higher gravity flow pipe.

⎟⎟⎟⎟

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⎞

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⎝

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ZZQQ

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Storm water pumping stations shall be designed to handle the projected runoff for specific catchments. However, their capacity may be larger in order to ensure that clear times for upstream detention ponds are met. Pump controls shall be based primarily on water elevations in the wet well of the station. A SCADA system shall be used to ensure appropriate cycling of individual pumps based on run times. The pump operation shall be by simple float actuated start‐stop switches and constant speed pumps.

4.9.2 Wet Well Volume Wet well sizing is a function of the incoming flows, the control strategy for the station, the selected pumps, and the number of starts per hour permissible for the pumps. Recommended cycling frequency depends on the type of pump being used, the motor size and pump operating efficiency. For submersible pumps in the range of capacities likely to be used, the recommended cycle time ranges from 7 to 10 minutes; the equivalent of 6 to 10 starts per hour. For design purposes, pump stations shall have a minimum cycle time of 10 minutes. Cycle times are with respect to dry weather flows since during storm events there is little cycling of pumps.

For constant speed pumps, wet well volume is calculated based on cycling frequency when inflow to the station is about 50 percent of the pumping rate with a single pump operating.

The wet well volume shall be calculated from the basic formula:

CT = [V/(D‐Q)+(V/Q)] where

D = Pump rate (m³/min.)

Q = Inflow rate (m³/min.)

CT = cycle time (minutes between pump starts)

V = volume (m³)

Since “minimum” cycle time is of concern (Q = D/2), the formula reduces to CT = 2V/Q.

4.9.3 Wet Well Depth The depth of wet well below the required invert of the inlet pipe is a function of the following:

1. Required submergence to prevent vortexing in the pump suction piping which may cause unbalanced loading on impellers & bearings, thereby reducing pump life.

2. The minimum Net Positive Suction Head Required (NPSHR) by the particular pump impeller selection. This requirement is provided by the pump supplier.

3. High liquid level in the wet well being set at 0.8 times the inlet pipe diameter above the invert. This allows the inlet pipe to be emptied frequently preventing buildup of settled material in the gravity inlet pipes.

The required submergence refers to minimum liquid level above a vertical pump inlet flare or fitting and above the centerline of the flare if positioned horizontally.

The submergence shall be calculated as per Hydraulic Institute Standards.

The minimum submergence determination and NPSHR shall be verified during the wet well sizing.


4.9.4 Pump Selection Pump selection should be made to optimize conditions over the projected range of flows – minimum, average, maximum. Selection is made to minimize holding times in the wet well before pumping and maximizing efficiency. Actual pump selection can only be made after a system head capacity curve is developed for the proposed installation. The following items are to be considered:

1. Required range of head and flows

2. Number of pumps


4. Efficiency


Multiple pumps will be used to achieve the required pumping capacity. Using multiple pumps permits better station control and performance when flows vary from different intensity storm events. Also, smaller capacity individual pumps for low flows will serve better during the dry season when the only flows are from groundwater control.

If screw pumps are an appropriate option, a minimum of two pumps shall be installed. As screw pumps automatically pump with a variable output to match the incoming flow (up to their maximum capacity), pump selection is primarily a function of number of pumps and their maximum capacity.

4.9.5 Pumping Station Structures Pumping station structures should be designed to ensure a safe working environment for operation and maintenance staff as well as maximizing performance and minimizing costs. The following shall be incorporated:

6. Ventilation systems to meet applicable standards.

7. Provisions to facilitate removing pumps, motors, and other mechanical and electrical equipment.

8. Suitable and safe means of access to dry wells and to wet wells.

9. Wet wells configured to minimize turbulence.

Wet well controls of the encapsulated float type; although more sophisticated control may be considered. In all cases, control sensors located away from turbulence of incoming flow and pump suction.

4.9.6 Surge Protection Surges can be generated in the pumped supply system following power failures, pump starting or stopping and sudden valve operations. Need for surge limiting equipment to protect the supply system due to possible transient pressure variation shall be considered. The calculation of surge shall be carried out by appropriate methods and using the relevant general equations and surge calculation software according to the conditions specified by the designer and based on the most unfavorable operating


conditions. Where surge protection is found to be necessary, the designer shall size and specify the appropriate surge protection equipment.

4.9.7 Electrical and Instrumentation Systems All pumping stations shall be designed and constructed based on international principles. The following provisions shall be included:

1. Supply and control circuits allowing for disconnection from outside the wet well. Terminals and connectors protected from corrosion through proper location and/or the use of water tight seals. Separate strain relief.

2. Properly sealed motor control panels.

3. Ground fault interruption protection.

4. Power cords designed for flexibility and serviceability under conditions of extra hard usage and such that field connections are facilitated.

Instrumentation systems shall be consistent with other existing systems in use and integrated into the site wide centralized operational management system (SCADA control system).

New SCADA systems shall be compatible with the Master Station and will be monitored and the information compiled at the main master system locations, although remote stations may also be incorporated into the system.

4.9.8 Rising Mains Rising mains shall be sized to maintain velocities within an acceptable range for a variety of flow conditions. Rising main diameters should not be less than 200 mm. Selection of the diameter is dependent on the maximum and minimum flow rates required through the pipe, the characteristics of the pipe (length, material, and route) and velocity. Flows are set based on required clear times from drainage areas and detention ponds. Pipe characteristics are important since the head loss in the system should be minimized. Velocity is also a factor in the determination of head loss.

The minimum velocity must be achieved with only one pump in operation since this will be the condition during low‐flow periods.

All pressure service pipes beyond the limits of the pumping station shall be GRP with minimum pipe stiffness of 10,000 N/m2 within the limits of the pumping station and 5,000 N/m2 beyond the limits of the pumping station. As an alternative, ductile iron pipe and fittings may be used for pipes exposed in the wet well and valve vaults.

4.9.9 Air Valves and Washouts The rising mains shall be equipped with the following valves for facilitating the operation, control, and maintenance.

1. Air and Vacuum Valves: These valves shall be provided at summits along the pipe profile and along long stretches with uniform slope to purge out accumulated air in the pipe system. Air release and vacuum relief valves are often needed along transmission mains and may sometimes be unavoidable in sewage force mains. Air must be bled


slowly from high points to prevent (1) “air binding” and (2) the reduction of the cross section of the pipe at high points. Vacuum conditions must be prevented when the pump head drops quickly (as in power failures) to prevent column separation and at extreme high points in pipelines to prevent potential pipeline collapse due to vacuum. Vacuum relief valves can be as large as one‐sixth of the diameter of the transmission main, whereas air release valves may be as small as one‐fiftieth of the diameter of the pipe.

2. A combination of air and vacuum valves shall be provided at appropriate locations for quick air entry or vent to prevent cavitations and facilitate quick filling of the pipe. In general, air‐valves are to be installed at crest points, changes in elevations and in case of constant rising mains having moderate slope, at a maximum spacing of 1000 m to 1500 m.

3. Washout valves: These valves will be provided at low points or sags along the pipe profile. These valves facilitate flushing, repair or maintenance of the pipe wherever necessary.


5. Isolating Valves with diameter smaller than 300 mm shall be gate valves and larger diameter shall be eccentric plug valves or globe valves.

6. Non‐Return Valves: These valves will be provided in the pump station to prevent a reverse flow into the pumps and shall be of noiseless non‐slam type.

All valves not located in a pump station structure shall be installed inside reinforced concrete valve chambers.

4.9.10 Emergency Power Supply All pumping stations shall be provided with back‐up, stand‐by engine‐driven pumps or electrical power generators sized to power 100 percent of the rated pumping station capacity.

4.9.11 Reliability For reliability, provide on‐line spares for all active equipment.

Attachment 4‐1

PA78

PA77

PA76

20-EA25

EF4

20-EA27

20-EA27

PA78

PA77

PA76

CATCHMENT-2

L E G E N D

CATCHMENT AREA BOUNDARY

( LENGTH )

( DIAMETER )

ROAD MANHOLE

MANHOLE No.CATCHMENT No.

GROUND LEVELINVERT LEVEL

ROAD GULLY

Sample Calculations - based on Tripoli Intensity-Duration-Curve

(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)(1) (2) (3) (4) (5) (6) (7) (8) (9) (10) (11) (12) (13) (14) (15)C coef.

Green Area

Residential Roads Section Total time of entry

Travel time

Accu.

m c=.25 c=.6 c=0.9 m2 Ha mm/hr m3/d l/sec

1 2 40.5 185 332 357 874 0.0874 0.648 15.00 0.00 15.00 56.40 767.16 8.882 3 22 1360 350 530 2240 0.3114 0.458 15.00 0.90 15.90 54.27 1,859.65 21.523 4 23.5 1564 295 686 2545 0.5659 0.466 15.90 0.49 16.39 53.20 3,365.32 38.954 5 10.44 299.15 74 228.85 602 0.6261 0.540 16.39 0.52 16.91 52.11 4,229.15 48.955 6 32.72 165.5 0 94.5 260 0.6521 0.486 16.91 0.23 17.14 51.64 3,929.95 45.49

Node Pipe Length

Area Total Area Time of Concentration

From To C Ave.min

Q=CIA

Q(m3/s)Rainfall intensity

5 6 32.72 165.5 0 94.5 260 0.6521 0.486 16.91 0.23 17.14 51.64 3,929.95 45.496 7 31.36 253 736.6 455.4 1445 0.7966 0.633 17.14 0.73 17.87 50.25 6,083.22 70.41

(16) (17) (18) (19) (20) (21) (22) (23) (24) (25) (26) (27) (28)D S % Vfull Q/Qfull Ground Elevation Invert Elevation Depthmm m/m m/sec m3/sec l/sec (m)

From To From To From To315 0 005 1 021 0 101 101 34 0 09 703 76 703 50 702 16 701 96 1 60 1 54

Qfull (m)(m)

315 0.005 1.021 0.101 101.34 0.09 703.76 703.50 702.16 701.96 1.60 1.54315 0.005 1.021 0.101 101.34 0.21 703.50 703.40 701.96 701.85 1.54 1.55315 0.005 1.021 0.101 101.34 0.38 703.40 703.30 701.85 701.73 1.55 1.57 1.67315 0.004 0.914 0.091 90.65 0.54 703.30 703.21 701.63 701.59 1.67 1.62400 0.004 1.071 0.171 171.40 0.27 703.21 703.02 701.59 701.46 1.62 1.56400 0.004 1.071 0.171 171.40 0.41 703.02 702.90 701.46 701.33 1.56 1.57

Manning Equation

v=(1/n)R(2/3)S(1/2)( / ) ( / )

n=0.010 for uPVCn=0.010 for GRP

Note:Colum 1 through 8 ‐ Input dataColumn 9 ‐ Composited C values based on land use of the drainage area

vfull=(0.397/n)D(2/3)S(1/2)

Qfull=(0.312/n)R(2/3)S(1/2)

i5(mm/hr) = 336.9*tc(time in mintes)(‐0.66)

Column 9 ‐ Composited C values based on land use of the drainage areaColumn 12 ‐ Time of concentration based of the longest travel pathColumn 16 ‐ Design pipe sizesColumn 21 ‐ Check pipe capacity ‐ the pipe are 9 % to 54 % fullColumn 26 through 28 ‐ Depth to the pipe invert

Figure 4A-1: Intensity-Duration-Curve for Misrata

Table 4A-1: Intensity-Duration- for Various Recurrence Intervals for Misrata

Rainfall Intensity, mm/hrTime,Minutes 2 Year 5 Year 10 Year 25 Year 50 Year 100 Year

5 57.23 110.08 152.41 213.14 262.99 316.21

10 36.47 70.15 97.13 135.83 167.60 201.51

15 28.02 53.90 74.63 104.36 128.77 154.83

30 17.86 34.35 47.56 66.51 82.06 98.67

60 11.38 21.89 30.31 42.38 52.30 62.88

90 8.74 16.82 23.29 32.56 40.18 48.31

120 7.25 13.95 19.31 27.01 33.33 40.07

360 3.55 6.83 9.46 13.23 16.32 19.62

720 2.26 4.35 6.03 8.43 10.40 12.50

1440 1.44 2.77 3.84 5.37 6.63 7.97

0

40

80

120

160

200

0 10 20 30 40 50 60 70 80 90

Rai

nfal

l Int

ensit

y, m

m/h

r

Time, Minutes

5 Year

50 Year50-Year = 748.63*t-0.65

5-Year = 331.37*t-0.65

Figure 4A-2: Intensity-Duration-Curve for Derna

Table 4A-2: Intensity-Duration for Various Recurrence Intervals for- Derna

Time, minutes

Rainfall Intensity, mm/hr

2 Year 5 Year 10 Year 25 Year 50 Year 100 Year5 51.80 98.62 132.71 176.71 209.75 242.44

10 33.01 62.85 84.57 112.62 133.67 154.50

15 25.36 48.29 64.98 86.52 102.70 118.71

30 16.16 30.77 41.41 55.14 65.45 75.65

60 10.30 19.61 26.39 35.14 41.71 48.21

90 7.91 15.07 20.28 27.00 32.05 37.04

120 6.56 12.50 16.82 22.39 26.58 30.72

360 3.21 6.12 8.23 10.96 13.01 15.04

720 2.05 3.90 5.25 6.99 8.29 9.59

1440 1.31 2.49 3.34 4.45 5.29 6.11

0

40

80

120

160

0 10 20 30 40 50 60 70 80 90

Rain

fall

Inte

nsit

y, m

m/h

r

Time, minutes

5_Yr

50_Yr

50_yr = 41.71 *t -0.65

5_yr = 19.61* t-0.65

Figure 4A-3: Intensity-Duration-Curve for Benghazi - Benina Airport Data

Table 4A-3: Intensity-Duration for Various Recurrence Intervals for Benghazi

Time,minutes

Rainfall Intensity, mm/hr

2-Year 5-Year 10-Year 25-Year 50-Year 100-Year

5 112.81 185.74 239.46 285.86 318.18 339.12

10 68.87 117.06 152.18 184.59 207.18 223.12

15 51.60 89.36 116.73 142.92 161.19 174.65

30 31.5 56.32 74.19 92.29 104.95 114.91

60 19.23 35.49 47.15 59.59 68.34 75.60

90 14.41 27.10 36.16 46.14 53.17 59.18

120 11.47 22.37 29.96 38.48 44.50 49.74

360 5.37 10.76 14.61 19.24 22.54 25.62

720 3.28 6.78 9.28 12.42 14.68 16.85

1440 2.00 4.28 5.90 8.02 9.56 11.09

0

40

80

120

160

200

240

0 10 20 30 40 50 60 70 80 90

Rain

fall

Inte

nsit

y, m

m/h

r

Time, minutes

5-Year

50-Year50-Year = 861.67*t-0.619

5-Year = 542.52*t-0.666

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JUNE 2009 REVISION NO. 02 WATER Reuse for Landscape Irrigation 5‐1

5 Water Reuse for Landscape Irrigation HIB has developed standard design criteria for treated wastewater reuse and irrigation water transmission and distribution systems. The criteria presented reflect typical installations in the region and to support the design intent for treated wastewater reuse for landscape irrigation. It is understood that certain situations may require deviation from the criteria presented herein. All deviations shall be made only with the written HIB approval.

5.1 General The primary source of water for landscape irrigation will be reclaimed water. For the purpose of this document reclaimed water is defined as treated wastewater effluent that satisfies the minimum water quality criteria for reuse as defined in Irrigation Water Quality Standards Section 5.1.4. Reclaimed water can be augmented by other sources such as surface, groundwater and storm water runoff with chloride and total dissolved solids concentrations and other water quality parameters consistent with irrigation water quality criteria. Reclaimed water may also be used to supply water to fire hydrants connected along the pipeline routes. Fire hydrants on reclaimed water shall be designed to supplement rather than replace, or be used in lieu of, fire hydrants on potable water. Placement of fire hydrants using reclaimed water shall supplement and not overlap or conflict with the locations of fire hydrants on the water distribution system.

Regional irrigation water networks consist of three networks: supply, transmission, and distribution. Irrigation water supply is pumped directly from wastewater treatment plants to large regional bulk storage tanks equipped with irrigation transmission pumping stations. The transmission network delivers irrigation water to local storage tanks, or lined ponds, equipped with fire and irrigation distribution pumping stations. The distribution network delivers water to fire hydrants and local irrigation users. To maintain the integrity of the operations and control strategy for the regional irrigation water networks, neither the regional supply network, nor the transmission network, shall be tapped for direct irrigation use. For smaller, non‐regional irrigation networks, the supply network and transmission network can combined into one network with HIB written approval.

5.1.1 Irrigation Supply Reclaimed water supply system will consist of a network of pipes and pumping stations to deliver reclaimed water from wastewater treatment plants to regional bulk storage and transmission pumping facilities. This supply will be provided at a minimum pressure of 1.2 bars to points of delivery. End users will be required to provide storage facilities with capacity to hold the volume equal to at least one day of irrigation demand. A valve and meter chamber is required at the point of connection for remote monitoring and control. End user storage facilities are required to be located adjacent to existing road rights of way to allow maintenance access to the supply pipes. Connections to the reclaimed water supply network for direct use in applying water for irrigation is not allowed.

The reclaimed water supply network shall be operated, maintained, and controlled by the owner of the Sewage (wastewater) Treatment Plant or their designated authorized agency.

5.1.2 Transmission Network Several regional bulk storage and irrigation transmission pumping facilities are planned to deliver low pressure bulk water to end users 24 hours per day. Minimum transmission pressure will be 1.2 bar at any point of connection. In‐line booster pumping stations within the transmission network may be


necessary to achieve an economical balance between operation and capital cost of transmission pumping. Irrigation water transmission piping system will deliver irrigation water to local storage facilities. Valve and metering assemblies will be provided on the discharge to each local storage tank for remote monitoring and control of delivery volumes, flows, and pressures. Metering assemblies will consist of a flow meter, a back‐pressure sustaining valve, and a SCADA‐ready solenoid‐actuated flow control valve. Connections to the reclaimed water transmission network for direct use in applying water for irrigation is not allowed.

The reclaimed water transmission network shall be operated and controlled by the owner of the regional reclaimed water transmission network or their designated authorized agency.

5.1.3 Distribution Network Multiple local fire/irrigation storage and distribution pumping stations (provided by the end users) will deliver water at sufficient pressure for irrigation service to points of application over a period of 8 hours per day. Minimum distribution pressure will be 4.0 bar at the connection point for irrigation and at fire hydrants in the event of fire flow. The irrigation distribution network shall be designed with branches that can be isolated as needed for testing and cleaning. The distribution network should be sized to supply the required peak day irrigation demand based on anticipated peak season usage delivered over an 8‐hour period plus fire flow.

The reclaimed water distribution network shall be operated and controlled by the local entity or an authorized agency designated by HIB.

5.1.4 Irrigation Water Quality Standards The minimum standards of treatment required for treated wastewater used in irrigation systems are described below. The treated wastewater is divided into two classes:

1. Class A waters: Treated to secondary standard, sand filtered and chlorinated. The maximum E. coli level in the final effluent shall be less than 10 per 100 ml. This class can be used for unrestricted irrigation.

2. Class B waters: Treated to secondary standard and E. coli levels less than 1,000 per ml. This class can be used for restricted irrigation.

The following table further describes the type of irrigation activities for which the two water classes can be used.


Table 5—1. Permissible Water Classes for Irrigation Methods

Irrigation Method Permissible Water Class

Drip irrigation onto trees and bushes A or B

Low mist hand spray A or B

Spray irrigation in parks and green spaces (closed to public, after hours of use, or at least 2 hours before public use) A or B

Unlimited spray irrigation of public areas (with precautions to reduce mist formation)

A only

In both cases the Total Dissolved Solids (TDS) of the treated wastewater shall be less than 1,000 mg/l (which for reference is greater than potable water standard of 500 mg/l). Irrigation will either be drip/subsurface irrigation (in public areas) or spray irrigation (in non‐public areas). Thus, effluent treated to Class B standards will be acceptable.

In addition to reclaimed water, other sources such as groundwater and captured storm water runoff of acceptable quality, or potable water may be used to augment irrigation water supplies.

5.2 Irrigation Design Criteria

5.2.1 Irrigation Demands Irrigation demand is based on the design of each landscape area within the service area of each irrigation storage tank. Different plants have different irrigation demands which vary from season to season during the year. The network must be designed to meet the highest anticipated flow condition. For irrigation networks, the highest flow condition occurs during the season corresponding to peak irrigation water demand. Peak demand usually occurs during the peak growing season and summer months, with the highest evapotranspiration rates. The peak irrigation demand of different plant types are provided in Table 5—2. Average annual irrigation water demand will be substantially less than the peak season demand.


Table 5—2. Irrigation Demand by Plant Type

Plant type Daily irrigation demand1

Grass (Lawn) 10 mm/day

Deciduous Trees 7 mm/day

Olives Trees (high density) 5 mm/day

Citrus Trees 7 mm/day

1Source: Libyan Agricultural Master Plan: Crop Gross Irrigation Requirements: Zone A (Coastal Areas)

As plant palettes are developed, irrigation demand will become more defined for individual irrigation areas. Salt tolerant plants and drought tolerant plants will be used in areas where appropriate in order to decrease the overall irrigation demand.

5.2.2 Distribution Network

5.2.2.1 Hydraulic Calculations Hydraulic calculations shall be carried out in order to demonstrate that the system will:

• satisfy the estimated peak‐day demand delivered over an 8‐hour period plus fire flow;

• operate at acceptable velocities;

• operate within the required pressure range

5.2.2.2 Flow Velocities All irrigation network pipelines are pressure mains. Mains should be sized to keep friction losses under peak conditions to a manageable level. Selection of size requires an understanding of projected flows for the service life of the system. Maximum velocities may range up to 2.5 m/s, or as needed to not exceed a maximum head loss gradient of 10 m per kilometer.

5.2.2.3 Head Losses The head loss resulting from flows through a single main may be calculated using the Hazen‐ Williams Equation. Because most irrigation systems are networked, flows comes from several directions and head losses cannot be determined directly. If the system is small a manual calculation using a Hardy‐Cross method may used. For larger networks, hydraulic design of all networked systems shall be carried out using approved computer modeling software. Acceptable models are KYPIPE, PIPE2000, WaterCAD, H2ONet, Cybernet, EPAnet, and other equivalent commercially available models. Designs should be evaluated over a range of C values (100 to 140) or equivalent, to assess how the effects of pipe degradation will impact the overall system performance.

5.2.2.4 Pipe Materials Irrigation mains shall be capable of accommodating the pressure required for fire flows. Irrigation distribution mains from the end users’ secondary storage tanks shall be boosted with suitable pumps to


provide working pressures of up to 10 bar as needed to meet the minimum pressure for fire protection. Pipes materials such as GRP, HDPE, or PVC shall be used.

5.2.2.5 Minimum Cover Requirements For pressure pipes, minimum cover is 0.8 m below final finished or future grade in unpaved areas with no vehicular traffic and 1.0 m below final finished or future grade in paved areas with vehicular traffic. If the available cover is less than specified, then additional protection such as full concrete encasement or the use of concrete protection slabs may be required

The actual cover required for construction may be greater than that required solely for structural integrity. The maximum cover depth recommended is approximately 10 m. This maximum depth is consistent with typical pipe installation standards and manufacturer recommendations. Should the actual cover be greater than 10 m, pipe materials should be evaluated and a higher strength class of pipe utilized.

For pipes at less than these minimum values or installed at excessive depths, concrete encasement may be required to protect the pipe from damage. These should be looked at on an individual basis, and alternatives of different pipe size should be considered before designing the pipelines outside of the specified depth ranges. In all cases, the pipe minimum and maximum depths shall be in conformance with the pipe manufacturers’ recommendations.

5.2.2.6 Utility Crossings Utility crossings are recommended to be consistent with local standards and practices. The guidelines, based on internationally accepted standards, are shown in Table 4‐3.

Table 5—3. Utility Crossing for Irrigation Pipes


Vertical Clearance - 30 cm (if less than 30 cm, use concrete saddle) - Carry encasement to first joint on each side of crossing

Horizontal Clearance - 3.0 m - Where available corridor space is limited, minimum clearance

may be reduced to 1.2 m assuming structures can overlap into adjacent corridors.

- If in same trench, place other utility on separate bench on undisturbed soil above the line

Potable Water Lines - Always place above irrigation lines

Irrigation pipes crossing under roads shall be aligned at 90 degrees or perpendicular to the road with all bends located beyond the limits of the road pavement and curbs.


5.2.2.7 Thrust Blocks Concrete thrust blocks shall be provided at tees, elbows, reducers, and other fittings in order to prevent their movement due to pressure of the pipes. Design pressures for thrust restraint shall be 10 bar in all irrigation mains. Soils bearing allowances shall be according to normal allowances for the type of soil encountered.

5.2.2.8 System Valves The irrigation water mains and distribution system will be equipped with the following valves for facilitating the operation, control, and maintenance of the system. The design consultant shall take into account the proper distribution of valves along the system.

Air Release Valves: These valves shall be provided at summits along the pipe profile and along long stretches with uniform slope to purge out accumulated air in the pipe system. A combination of air and vacuum valves shall be provided at appropriate locations for quick air entry or venting to prevent cavitations and facilitate quick filling of the pipe. In general, air‐valves shall be installed at crest points, change in elevations and in case of constant rising mains having moderate slope, at a maximum spacing of 600 m.

Washout valves: These valves shall be provided at low points or sags along the pipe profile. These valves facilitate flushing, repair or maintenance of the pipe wherever necessary.

Isolating valves: shall be located at branching points on the network as a provision for flushing, testing, and maintenance. The number and distribution of these valves shall be in a manner that ensure minimum disturbance to the supply of irrigation water in case of maintenance or repair works. The maximum allowable distance between isolating valves on the distribution lines shall not exceed 500 m. In general, isolation valves shall be provided on all branches from feeder mains and between two washout valves. In the transmission mains where there are no intermediate branches, isolating valves shall be provided at a maximum distance of every 2 to 3 kilometers. In the transmission mains, profile of the pipeline and location of washout and air valves is also to be considered while locating the isolation valves. Isolation Valves with diameter 300mm and smaller shall be gate valves and larger diameter isolation values shall be butterfly valves.

Non‐Return Valves: These check valves shall be provided in the pumping station to prevent a reverse flow into the pumps and shall be of noiseless non‐slam type.

Control valves: These valves shall be motorized butterfly or diaphragm type globe valves, operated to control the flow and pressure at the consumer end while supplying to different tanks distribution system with varying elevation and flow requirement.

All valves not located in a pumping station structure shall be installed inside reinforced concrete valve chambers.

5.2.3 Flow Meters and Structures Flow meters shall be of the remote reading type and allow reading without physical access to the structure. The meters shall be housed in suitable protective and totally enclosed structures which will allow easy access when required for maintenance.


5.2.4 Storage There are two types of irrigation storage facilities planned. Bulk irrigation water storage will be supplied with water directly from the supply network, with storage volume equal to a minimum of one day of irrigation demand. Local fire/irrigation water storage will be supplied with water directly from the irrigation water transmission network with storage volume equal to a minimum of one day of irrigation demand plus two hours of fire flow.

Storage tanks are to be underground for aesthetic reasons. Above ground reservoirs or vertical tanks may be used where the vertical profile of the storage facilities is consistent with the surrounding land use and will not detract from the value of adjacent properties. Lined ponds may be used for storing water for irrigation of large landscaped areas such as a golf course, and in some cases may even provide an amenity feature.

Storage tanks shall be reinforced concrete structures with adequate safe access and cleanout capabilities. If above ground storage is considered, it shall be hidden or screened from view from outside the development. Above ground tanks may be reinforced concrete or glass‐coated steel structures. Storage tanks shall be completely covered to block exposure to sunlight to limit the potential of algae growth. Pond storage facilities are exempted from this provision.

Storage tanks will be provided with wash‐down capability. Storage tanks shall be compartmentalized to allow one compartment to be taken out of service for cleaning while maintaining pumping operations. Compartments will be isolated by motor‐actuated sluice gates or penstocks. Tank bottoms shall be sloped to one end to facilitate cleaning and draining. Multiple hose connections to pressurized irrigation water shall be provided in close proximity to tank manhole access ports for flushing and cleaning the tanks. Tank manhole access ports shall be located at spacing that will facilitate the wash down and cleaning by a man holding a hose and nozzle from the top of the structure without man‐entry inside the tank being required.

Storage tank piping shall have mechanical float valves for protection from overflow on filling. All metal components inside the storage tank or otherwise in contact with the treated wastewater shall be constructed of corrosion resistant materials.

5.2.5 Pumping Stations Pumping stations at Bulk Irrigation Water Storage and Transmission Pumping Stations will have a stand‐alone building with a pump room, electrical room, generator room with fuel storage for back‐up emergency power, and a SCADA monitoring and control station. The pump room will include pumps, valves, automatic backwash strainers, hydraulic surge protection, and a traveling bridge crane. For vertical turbine pumps, provide roof hatches directly over the top of the pumps of sufficient size to allow complete removal of the combined drive and pump using a mobile crane. The electrical room will include switchgear, emergency power transfer switches, motor control centers, and SCADA monitoring and control equipment with a work station.

In‐line booster pumping stations may also be used at several locations in the transmission mains system to more efficiently maintain delivery pressures throughout the transmission network.

Pumping stations at Local Fire/Irrigation Water Storage and Distribution Pumping Stations will be a scaled‐down version of the Bulk Irrigation Water Storage and Transmission Pumping Station with special provisions for additional fire pumps. In most cases, pumping stations will take their suction directly


from the storage tank. If a wet‐well is designed separate from the storage tank or pond, it should be sized using standard guidelines for such facilities. The wet‐well and connection from the storage facility shall be such that there is no chance for draining to the shutoff level during an irrigation or fire flow event.

For vertical turbine pumps, verification that intakes are configured and sized in accordance with applicable Hydraulic Institute standards is required during the design process. Verification of compliance with Hydraulic Institute standards for vertical turbine pump intakes shall not be deferred to the construction contractor.

The minimum required fuel storage capacity will be a function of the reliability of local power and fuel delivery. Where local power and fuel delivery is consistently and reliably available, then a minimum of one‐day's fuel storage should be sufficient. Where power and fuel delivery is not consistent and reliably available, then the capacity of fuel storage will need to be increased to fit the local conditions.

5.2.5.1 Pump Selection Pumps shall be selected to optimize conditions. Selection shall be made to maximize pumping efficiency under variable flows and pressures. Where possible, variable speed drives should be used.

Acceptable pumps are horizontal split case pumps and vertical turbine pumps, either wet well or can type. In very small systems, rotary lobe pumps may be considered.

Actual pump selection for the proposed networks will be made based on system head‐capacity curves under various flow conditions. The following are to be considered in the design of an irrigation pumping system:

1. Required range of head and flows – band of operating pressures expected

2. Number of pumps


4. Efficiency


Adaptability is important because initial flows may be significantly lower than design‐year flows. When this is the case, the selected pump(s) should be in the mid‐range of available impeller sizes so that simple changes in impellers can be made to improve pumping station capacity. Use of variable speed drives will greatly simplify such considerations.

5.2.5.2 Booster Pumping Stations The large area of coverage and variable topography of the irrigation system makes it inefficient to provide all areas adequate pressure under all conditions in a single pressure zone. Therefore, booster pumping stations may be used at several points in the transmission network to maintain minimum delivery pressures at higher elevations or at remote locations from the storage sites. The location of the booster pumping stations will be based on the modeling developed for the TSE irrigation system.


5.2.5.3 Surge Pressure Limiting Equipment Pressure transients or surges can be generated in the pumped supply system following power failures, pump starting or stopping, and sudden valve closure. If not controlled, these may cause pipe damage or pipe failure in extreme instances. Consideration shall be given to the need for surge limiting equipment to protect the supply system due to possible transient pressure variation. The calculation of surge shall be carried out by appropriate methods and using the relevant general equations and surge calculation software according to the conditions specified by the designer and based on the most unfavorable operating conditions. Where surge protection is found to be necessary, the designer shall size and specify the appropriate surge protection equipment.

5.2.5.4 Pumping Station Facility Building Aboveground pumping station structures will be located immediately adjacent to storage facilities. The architectural detail of pumping stations shall blend with the architectural scheme of the surrounding area. Pumping station structures shall be designed to ensure a safe working environment for operation and maintenance staff as well as maximizing performance and minimizing costs.

The pumping station shall be located adjacent to paved public roads for maintenance vehicle access. For sites that are not located adjacent to a paved public road, a reservation of a 10 meter wide access way from landlocked lots and to paved public roads shall be provided.

Provisions shall be made to facilitate removal and replacement of major equipment including pumps, motors, switchgear, and other mechanical and electrical equipment. Lift equipment and adequate access openings shall be provided for equipment removal and replacement.

5.2.6 Fire Hydrants The requirement for water for fire‐fighting purposes shall be determined in accordance with local regulations. Where the irrigation distribution network is combined with fire flows, the irrigation network shall be adequately designed to meet the minimum requirement of fire flows and pressure in accordance with established standards. Criteria for hydrant assembly spacing shall be as indicated in Section 1 – Water Design Standard.

Fire hydrant assemblies shall be connected to irrigation distribution mains at various intervals depending on the type of road. Placement of fire hydrants shall supplement and not overlap or conflict with the locations of fire hydrants on the water distribution system.

All connections to irrigation systems shall be at hydrant leads located just upstream of the hydrant isolation valve in the hydrant assembly.

5.2.7 Electrical and Instrumentation Systems All pumping stations shall be designed and constructed based on internationally accepted principles. The following provisions shall be included:

1. Supply and control circuits allowing for disconnection from outside the wet well. Terminals and connectors protected from corrosion through proper location and/or the use of water tight seals. Separate strain relief.

2. Properly sealed motor control panels.


3. Ground fault interruption protection.

4. Power cords designed for flexibility and serviceability under conditions of extra hard usage and such that field connections are facilitated.

Instrumentation systems shall be consistent with other systems in use and integrated into the existing centralized operational management system using a SCADA monitoring and control system. Where there are no existing systems, the instrumentation shall be designed to be SCADA ready.

The SCADA system shall be compatible with the Master Station and will be monitored and compiled at the main master system locations, although remote stations may also be incorporated into the system.

JUNE 2009 REVISION NO. 02 STANDARDS for Barrier‐Free Design 6‐1

6 Standards for BarrierFree Design

6.1 Introduction

6.1.1 Purpose These Standards are intended to inform designers and contractors providing services to the Government of The Great Socialist People’s Libyan Arab Jamahiriya of the minimum requirements for barrier‐free design.

6.1.2 Application “The Government of The Great Socialist People’s Libyan Arab Jamahiriya” shall insure that the design of buildings, structures and premises, or parts of buildings, structures and premises, that it purchases, constructs or significantly renovates after these standards come into force complies with the guidelines before occupation or regular use by its Residents. These Standards will be applied and implemented on a “go‐forward” basis.

‘Significant Renovation’, The Housing and Infrastructure Board are encouraged to apply these Standards to renovations or changes of smaller spaces and other projects where possible.

The following definitions further clarify application of these Standards:

6.1.3 Definition of Significant Renovation These Standards will apply to renovations or changes to government owned or occupied spaces of at least 1000 square meters or where 50% of the floor space is affected.

Significant renovations do not include projects limited only to repairs or restoration to wall finishes.

6.1.4 Maintenance It is essential that barrier‐free paths of travel and facilities be properly maintained in accordance with other applicable legislation or standard maintenance practices in order to reduce the creation of new barriers. Some examples of maintenance items include:

1. Timely repair of uneven surfaces; 2. Removal of furniture, fixtures and stored items that impede clearance spaces or corridor widths; 3. Proper leveling of elevators; 4. Adjustment of door closers and elevator doors to prescribed limits; 5. Maintenance of prescribed lighting levels; and 6. Proper maintenance of non‐glare surfaces.

6.1.5 Emergency Evacuation Planning Facility Emergency Evacuation Planning should address accessibility procedures for persons with disabilities. Persons with disabilities who regularly occupy a facility should have access to Emergency Evacuation Plans in a range of formats, including large text and electronic formats. This will help to


improve the understanding of evacuation methods and promote adequate training of persons with disabilities of the emergency measures.

6.2 Exterior Areas

6.2.1 Parking and DropOff Areas

6.2.1.1 Provide a minimum number of barrier‐free car parking spaces in each parking area as follows:

Total parking spaces provided Minimum barrier‐free car spaces

required 1 ‐20 1 21 ‐100 2 101 ‐150 3 151 ‐200 4

over 200 1 additional for each additional

50 spaces or part thereof

6.2.1.2 Barrier‐free car parking spaces shall have a minimum width of 2400mm plus a 1500mm wide access aisle. The access aisle must be level. Length of the space shall be 5500mm. Two adjacent spaces may share the same access aisle Figure 6—1.

Figure 6—1: Barrier‐Free Car Parking Spaces


Figure 6—2: Symbols


6.2.1.3 In addition to the barrier‐free car spaces described in 6.2.1.1, provide a minimum number of van parking spaces in each parking area as follows:

Total Spaces Provided Minimum van spaces required 1 – 50 1

51 – 3002 2 301 – 700 3 Over 700 4

6.2.1.4 Barrier‐free van parking spaces shall have a minimum width of 3500mm plus a 1500mm wide access aisle to accommodate vans with built‐in wheelchair lifts. The access aisle must be level. Length of the space shall be as required but at least 6000mm. Two adjacent spaces may share the same access aisle Figure 6—3.

Figure 6—3: Barrier‐Free Van Parking Spaces

6.2.1.5 Barrier‐free car and van parking spaces shall be located as close as possible to the main accessible entrance of the building and shall lead directly to the building entrance without crossing any drive aisles. Provide a curb ramp (that will not be blocked by a parked vehicle) directly adjacent to the designated spaces. The accessible route shall be clearly marked.

6.2.1.6 The surface of all barrier‐free parking spaces must be level (maximum slope in any direction 2%), firm (no gravel) and slip‐resistant. Pavement markings must use non‐slip paint. Do not paint the entire surface of the parking space.

6.2.1.7 Provide signage to designate the barrier‐free spaces as reserved for permit holders: a) A vertical post‐mounted sign in front of the space, with the center of the sign between

1500mm and 2000mm above the ground (Figure 6—4); and b) A painted pavement marking in the center of the space, in contrasting color to the

pavement, 1000mm in length, with the International Symbol of Access – see Figure 6—2.


6.2.1.8 Provide an additional sign at van spaces labeled “Van Accessible.”

6.2.1.9 Provide a passenger pick‐up area at or near the main accessible entrance. The access aisle on passenger side shall be minimum 1500mm wide by 6000mm long.

6.2.1.10 Barrier‐free parking spaces and passenger pick‐up areas shall have a minimum clear height 2850mm, including along the vehicular access/egress route.

6.2.1.11 Provide a call button or two‐way communication system at all underground parking areas that have accessible parking spaces.

Figure 6—4: Vertical Parking Sign


6.2.2 Walkways and Ramps

6.2.2.1 Provide an accessible route from streets and parking areas to all accessible entrances. The accessible route shall be minimum 1600mm wide. Surfaces shall be maximum 5% (1:20) running slope and maximum 2% (1:50) cross slope. Where running slope must exceed 5% (1:20), provide a ramp in accordance with 6.2.2.6

6.2.2.2 Walkways and ramps shall have an even, firm, slip‐resistant surface. Where a level change is 75 mm or more, a handrail is required and must comply with this section.

6.2.2.3 Where the accessible route is adjacent to a vehicular route, it shall be separated from it by a cane‐detectable curb or railing.

6.2.2.4 Accessible routes must be free from overhead protrusion hazards. Provide a cane‐detectable railing, planter or bench anywhere that the overhead clearance is less than 2 m (Figure 6—5).

6.2.2.5 Where possible, locate gratings out of the accessible route. Any gratings in accessible routes walkways must be level and have a maximum 13mm wide opening in the direction of travel.

6.2.2.6 A sloped walkway shall be designed as a ramp wherever the gradient exceeds 5% (1:20). Exterior ramps shall have: a) Minimum width of 900mm between handrails; b) Maximum gradient of 8% (1:12); c) Level area of at least 1670mm by 1670mm at the top and bottom of the ramp. d) Level area of at least 1670mm long and at least the same width of the ramp at intervals of

not more than 9m along its length, where there is a change in direction of the ramp and at any intermediate doors along the length of the ramp;

e) Handrails on both sides as described in section 2.1.3; f) A wall or guard on each side that is not less than 1070mm above the ramp surface; and g) Edge protections in the form of curb or rail (Figure 6—7).

Figure 6—5: Overhead Hazards


Figure 6—6: Cane Detectable Obstructions


Figure 6—7: Ramp Edge Protections

6.2.2.7 Ramps shall have a color contrasting, textured, detectable warning surface in accordance with section 6.4.7.2 at the top and bottom a minimum of 920mm from the start of the slope, extending the entire width of the stair or ramp.

6.2.2.8 Where the location of the ramp is not readily evident from the main access route, provide a sign incorporating the International Symbol of Accessibility and a directional arrow indicating the location (Figure 6—2).

6.2.2.9 Provide curb ramps at all level changes along barrier‐free paths of travel. Curb ramps shall have: a) Maximum gradient of 13% (1:7.5); b) Minimum width of 1200mm (exclusive of flared sides); c) A surface (including flared sides) that is slip‐resistant, color and texture contrasted with

adjacent surfaces; d) A smooth transition from the curb ramp to the adjacent surfaces; and e) Flared sides with a slope of not more than 10% (1:10).

6.2.2.10 Provide a detectable hazard surface wherever a walkway adjoins a hazardous area such as an unprotected drop‐off, edge of a pool or to separate a walkway from a drive aisle that is at the same level.

6.2.2.11 Provide a level area in accordance with section 6.2.3.7 adjacent to all accessible entrance doors.


Figure 6—8: Curb Ramps


6.2.3 Entrances and Exits

6.2.3.1 For new buildings, all public entrances shall be barrier‐free. For existing buildings, as many as feasible (but no less than one‐half of all public entrances) shall be barrier‐free. Provide signage incorporating the International Symbol of Accessibility (Figure 6—2) to indicate the location of all barrier‐free entrances. The barrier‐free entrance must connect the exterior accessible route with the interior accessible route. Where an entrance consists of multiple doors beside each other, only one door in each set need be barrier‐free.

6.2.3.2 All required exits from the ground level must be barrier‐free. Signage incorporating the International Symbol of Accessibility (Figure 6—2) shall indicate the location of the barrier‐free exits.

6.2.3.3 Clear glass doors and sidelights at the entrances shall have a 100mm wide contrasting color strip mounted continuously 1350mm above the floor.

6.2.3.4 Two doors in series (such as in vestibules) shall have minimum 1200mm clear between the open doors (Figure 6—9).

Figure 6—9: Vestibule Clearance


6.2.3.5 Loose floor mats that can cause a tripping hazard or impede wheelchair use are not permitted in the barrier‐free path of travel.

6.2.3.6 Barrier‐free entrance and exit doors shall be a minimum of 915mm wide, such that frame stops, the door thickness and horizontal hardware such as panic bars shall not reduce the clear width of the doorway to less than 865mm (Figure 6—10).

Figure 6—10: Door Clear Width

6.2.3.7 Provide a minimum clear level space on both sides of doors as follows: a) 1500mm x 1500mm on the pull side; b) 1200mm x 1200mm on the push side.

6.2.3.8 At least one door in every barrier‐free entrance and exit (including doors leading from parking areas to the building) shall be equipped with an automatic operator. If there are two doors in series (vestibules), both doors shall have an automatic operator. Doors shall remain open a minimum of 5 seconds and shall take a minimum of 3 seconds to close from a 70 degree position. Pushbuttons, key switches, and card readers shall be located in conformance with 6.4.5. If the automatic door is a swinging door, provide a cane‐detectable guard rail with a horizontal member no more than 680mm above the ground (Figure 6‐11).

Figure 6—11: Cane Detectable Railing


6.2.3.9 Doors shall have lever hardware, push/pull plates, or exit devices (panic hardware). Round knobs and thumb‐latches are not acceptable.

6.2.3.10 Any exterior door not equipped with an automatic operator shall require a maximum force of 38N to open. Door closers shall take a minimum of 3 seconds to close from a 70 degree position.

6.2.3.11 Where a revolving door is used, an adjacent barrier‐free swinging door shall be provided.

6.2.4 Exterior Amenities

6.2.4.1 Where exterior amenities such as outdoor seating, terraces, playgrounds etc. are provided, ensure that they include accessible components. Tables and seating areas shall have clearances in accordance with section 6.4.9.

6.2.4.2 Where picnic tables or outdoor seating are provided, ensure at least some are placed on a hard surface, and are accessible from the barrier‐free walkways. If only some are barrier‐free, provide signage incorporating the International Symbol of Accessibility indicating the locations.

6.2.4.3 Where kiosks or pay booths are intended to be used by pedestrians, ensure that at least one window is located at a maximum of 860mm above grade and has an even, level (maximum 2%) access clearance area of not less than 750mm x 1200mm.

6.3 Interior Areas

6.3.1 Stairs and Ramps

6.3.1.1 Interior stairs shall have: a) Closed risers; b) Maximum rate of 60%; c) Uniform riser height (180mm high maximum) and tread depth (280mm deep minimum); d) Maximum nosing projection of 38mm, with a bevel or radius between 6mm and 10mm

and no abrupt underside; e) Color contrasting, slip‐resistant nosings 40‐60mm deep; f) Minimum light level of 100 lux; and g) Detectable warning surfaces as per 6.4.7 at top of the stairway.

6.3.1.2 The underside of all open stairs, escalators and other overhead features must be protected by cane‐detectable railings, planters or benches anywhere the overhead clearance is less than 2030mm. (Figure 6—5)

6.3.1.3 Handrails shall: a) Be provided on both sides of all stairs and ramps; b) Be continuous, except where other paths of travel intercept;


c) Be mounted at a uniform height between 865mm and 920mm above the stair nosing or ramp level;

d) Have an extension of 300mm beyond the top riser and 300mm plus the tread depth at the bottom riser;

e) Have returns (to a post, wall or floor) at all terminations; f) Have a continuous (without interruption by newel posts) graspable profile of 30 ‐ 43mm,

with a minimum clearance of 50mm to the adjacent wall; g) Be free of sharp or abrasive elements; and h) Be color‐contrasted from the adjacent wall surface.

6.3.1.4 Sloped floors shall be designed as a ramp where the gradient exceeds 5% (1:20). Interior ramps shall have: a) Minimum width of 900mm clear between handrails; b) Maximum gradient of 8% (1:12); c) Level area of at least 1670mm by 1670mm at the top and bottom of the ramp;

6.3.1.5 Except where the location of the ramp is clearly evident, provide signs incorporating the International Symbol of Accessibility indicating the location of the ramp.

Figure 6—12: Handrails


6.3.2 Lobbies and Corridors

6.3.2.1 All floor levels above or below the main accessible level that are used by the public shall be accessible by ramps (section 6.2.2) or elevators (in accordance with section 6.3.3).

6.3.2.2 Interior barrier‐free routes shall be minimum 1100mm wide with a 1600mm by 1600mm turn‐around space a minimum of 30m apart.

6.3.2.3 Corridors shall be free from overhead and protrusion hazards. Any overhead obstruction shall be minimum 2030mm high. Any horizontal projection more than 100mm into the corridor that is less than 2030mm high shall have a cane‐detectable warning no more than 680mm above the floor (Figure 6—5).

6.3.2.4 Wherever a turnstile is used, it shall have a gate directly adjacent with a clear width of at least 865mm. Where the location of the gate is not readily apparent, a sign shall indicate its location.

6.3.2.5 All floor surfaces shall be hard, level, slip‐resistant, non‐glare. Carpets shall be non‐static and short, dense pile. Floor patterns shall not be visually confusing.

6.3.2.6 Any gratings or drains in floors shall have maximum 13mm openings in either direction.

6.3.2.7 Provide a detectable hazard surface in accordance with section 3.7.3 wherever a walkway adjoins a hazardous area such as an unprotected drop‐off or the edge of a pool.

6.3.3 Elevators and Lifts

6.3.3.1 All passenger elevators layouts shall comply with Figure 6‐27.

6.3.3.2 Ensure that the emergency communication within the elevator is clearly audible. Do not permit the playing of any music in elevators.

6.3.3.3 Provide a mirror on the back wall of the elevator to assist people in wheelchairs and scooters in backing out of the elevator. However, mirrors on sidewalls should not be permitted due to visual distractions and confusion.

6.3.3.4 Loose mats and loose flooring are not permitted in elevators or lifts.

6.3.3.5 Platform lifts shall be permitted only if the persons using them can independently operate them. Lifts that require a key or assistance from another person are not acceptable.

6.3.3.6 Provide an LED‐messaging system in each elevator to enable communication in the event of an emergency with persons who are deaf or hard of hearing.

6.3.3.7 Provide voice‐activated speakers in all elevators.


6.3.4 Interior Doors and Doorways

6.3.4.1 Doors shall be a minimum of 915mm wide, such that frame stops, the door thickness and horizontal hardware such as panic bars shall not reduce the clear width of the doorway to less than 850mm.

6.3.4.2 All doors shall have lever hardware, push/pull plates, exit devices (panic hardware) or automatic operators. Knobs and thumb‐latches are not acceptable.

6.3.4.3 Unless the door is equipped with an automatic operator, provide clearance beside doors as follows: a) 300mm clear beside latch at push side of door b) 600mm clear beside latch at pull side of door

6.3.4.4 Any interior door not equipped with an automatic operator shall be single hand operation and require a maximum force of 22N to open. Door closers shall take a minimum of 3 seconds to close from a 70 degree position.

6.3.4.5 Thresholds shall be maximum 13mm high. Where over 6mm high, shall be beveled at a slope of not more than 1:2.

6.3.4.6 Doors shall have vision panels, either in the door or in a directly adjacent sidelight, except where privacy concerns make them unfeasible. Vision panels shall have the bottom edge no more than 900mm above the floor and no more than 250mm from the latch side of the door.

6.3.4.7 Clear glass doors and sidelights at the entrances shall have a 100mm wide contrasting color strip mounted continuously 1350mm above the floor.

6.3.4.8 Two doors in series (such as in vestibules) shall have a minimum 1200mm clear between the open doors.

6.3.4.9 Provide a minimum clear level space on both sides of doors as follows: a) 1500mm x 1500mm on the pull side. b) 1200mm x 1200mm on the push side

6.3.4.10 Where a revolving door is used, an adjacent barrier‐free swinging door shall be provided.


Figure 6—13: Door Clearances


6.4 Facilities

6.4.1 Washrooms/Bathrooms/Toilets

6.4.1.1 Every floor that is served by washrooms shall have either: a) A barrier‐free individual washroom as described in Figure 6‐17; or b) A barrier‐free water closet stall, lavatory and accessories

6.4.1.2 For new buildings, or where the extent of renovation includes reconfiguration of washrooms (i.e., new fixture locations), only section 6.4.1.1a is permissible. For renovations where this option is unfeasible, section 6.4.1.1b is acceptable.

6.4.1.3 Barrier‐free individual washrooms shall have: a) A door that complies with section 6.3.4; b) An automatic operator with the ability to be locked from the inside; c) A minimum area of 3.5 square meters, with minimum dimension between opposite walls

of 1.7m; d) A clear turning radius of 1500mm (does not include space under lavatory) e) A water closet that complies with section 6.4.1.5; f) A lavatory that complies with section 6.4.1.7; g) A shelf or counter at least 200mm x 400mm, mounted not more than 1000mm above the

floor; h) A coat hook mounted not more than 1200mm above the floor and projecting not more

than 40mm; i) An automatic hand dryer or paper towel dispenser mounted in accordance with 6.4.5; j) Washroom accessories (such as soap dispensers, vending machines, waste receptacles,

etc.) that comply with section 6.4.5; and k) An emergency call button.

6.4.1.4 Barrier‐free facilities within a multi‐fixture washroom shall have: a) A door that complies with section 6.3.4, with an automatic operator, or be designed so

that no door is necessary; b) If there are two doors in series, there shall be at least 1200mm clear between them when

open; c) At least 1500mm x 1500mm clear space in front of the barrier‐free water closet stall; d) At least 750mm x 750mm clear space in front of each barrier‐free lavatory; e) At least one barrier‐free water closet stall; f) At least one lavatory that complies with section 6.4.1.7 (in new buildings, all lavatories

shall comply); g) If urinals are provided, at least one urinal shall comply with 6.4.1.6; h) A shelf or counter at least 200mm x 400mm, mounted not more than 1000mm above the

floor;


i) Washroom accessories (such as soap dispensers, paper towel dispensers, hand dryers, vending machines, waste receptacles, etc.) shall comply with section 6.4.5; and

j) An emergency call button.

6.4.1.5 Barrier‐free water closets shall: a) Be located between 460mm and 480mm from the adjacent side wall; b) Have a transfer space at least 900mm wide clear on the open side; c) Have a back support where there is no seat lid or tank; d) Have a seat height of 430mm to 460mm above floor; e) Have flush controls that are automatic, or are located on the transfer side of the water

closet; f) Have two grab bars:

I. One 600mm long, mounted horizontally, centered on the water closet at a height of 840mm to 920mm above the floor (or 150mm above the tank where there is one), and

II. One L‐shaped, 760mm x 760mm, mounted with the horizontal portion at a height of 750mm to 900mm above the floor, and the vertical component mounted 150mm in front of the water closet OR one 760mm long, mounted diagonally, sloping upwards at an angle of 30º to 50º, with the lower end 750mm – 900mm above the floor and 50mm in front of the toilet bowl; and

g) Have a non‐regulating toilet tissue dispenser mounted in line with the front of the water closet, between 600mm to 700mm above the floor.

6.4.1.6 Barrier‐free urinals shall: a) Have a clear space of at least 750mm wide by 1200mm deep (including under the urinal); b) The urinal rim no higher than 430mm above the floor; c) Flush controls no higher than 1200mm above the floor; and d) Vertical grab bars on both sides, minimum 600mm long, mounted with the bottom

between 600mm – 650mm above the floor, maximum 380mm from the centerline of the urinal.

6.4.1.7 Barrier‐free lavatories shall: a) Have a centerline located at least 460mm from the adjacent side wall; b) Have the top of the counter or lavatory located no more than 840mm above the floor; c) Have a clear space of 750mm x 750mm in front of the lavatory; d) Have clearance beneath the lavatory of at least:

I. 760mm wide; II. 735mm high at the front edge; III. 685mm high at a point 205mm back from the front edge; IV. 230mm high over a distance from a point 280mm back from the front edge to

430mm back from the front edge;


e) Be equipped with automatic faucets, or faucets with lever handle(s) at least 75mm long, that are located not more than 485mm from the front of the counter or front edge of lavatory, that are not spring‐loaded;

f) A mirror mounted with the bottom edge as low as possible, but not more than 1000mm above the floor;

g) Temperature controlled water to not exceed 55 degrees Celsius; and h) A soap dispenser mounted within 500mm of the lavatory, no higher than 1100mm,

operable with one hand.

6.4.1.8 Grab Bars shall be: a) Slip‐resistant; b) Diameter of 30mm‐40mm; c) Have a clear space of 30mm – 40mm from the wall; and d) Be firmly mounted to resist a force of 1.3kN in any direction.

6.4.1.9 Barrier‐free water closet stalls shall have: a) A clear space inside of at least 1500mm x 1500mm, clear of the door swing; b) A door which provides at least 860mm clear width which is capable of being locked from

the inside using one hand, with a large thumb turn, with spring hinges to close automatically;

c) A water closet that complies with 6.4.1.5; and d) A hook mounted not more than 1200mm above the floor and projecting not more than

40mm.

6.4.1.10 Unless the barrier‐free washrooms are directly adjacent to the other washrooms, provide directional signage incorporating the International Symbol of Accessibility indicating the location.

6.4.1.11 Provide a motion detector control for lights in all barrier‐free washrooms. In a multi‐unit washroom, ensure that the sensor will detect motion within the barrier‐free stall.

6.4.1.12 Where toilet partitions are provided a minimum of 230mm toe clearance shall be provided (Figure 6‐17).

6.4.2 Shower and Bath Facilities

6.4.2.1 Wherever shower facilities are provided, provide at least one roll‐in shower that has: a) An interior clear area of at least 900mm x 900mm; b) A clear floor area in front of at least 900mm deep and the same width as the shower; c) A roll‐in threshold not exceeding 13mm high with a maximum bevel slope of 1:2; d) A floor drain located outside the shower stall; e) A horizontal grab bar on the side wall at least 600mm long, mounted between 700mm and

800mm above the floor;


f) A vertical grab bar on the opposite side wall at least 800mm long, mounted with the lower end between 600mm and 650mm above the floor and between 35mm and 65mm from the outside edge;

g) A horizontal grab bar on the back wall at least 900mm long, mounted 850mm above the floor;

h) A vertical grab bar on the back wall at least 600mm long, mounted with the lower end between 750mm and 850mm above the floor and between 400mm and 500mm from the side wall with the other vertical bar;

i) A flip‐up seat mounted on the side wall with the vertical bar; j) A hand‐held shower head on an adjustable pole; k) Controls mounted no more than 1200mm above the floor; and l) A slip‐resistant floor.


Clear Floor Space Requirement

Control Wall Elevation

915mm x 915mm Shower Plan

Figure 6—14: Barrier‐Free Showers


Figure 6—15: Barrier‐Free Bath Tubs


Plan

Elevation

Figure 6—16: Water Closet Details

Figure 6—17: Toilet Partition Details

6.4.2.2 Wherever bath facilities are provided, provide: a) A clear floor area in front of at least 760mm deep and the same width as the bath; b) A floor drain located outside the bath; c) A horizontal grab bar on the side wall at least 600mm long, mounted between 700mm and

800mm above the floor (Figure 6‐16);

6.4.3 Drinking Fountains

6.4.3.1 Drinking fountains shall have a spout that: a) Is located near the front of the unit; b) Is between 750mm and 900mm above the floor;


c) Directs the water flow parallel to the front on the unit; and d) Provides a water flow at least 100mm high.

6.4.3.2 Controls shall be automatic or operable with one hand using a force of not more than 22N.

6.4.3.3 Drinking fountains shall have a clear floor area of 750mm wide by 1200mm deep. All drinking fountains must be cane‐detectable, recessed or otherwise located out of the route of travel.

6.4.3.4 Cantilevered fountains shall have: a) Knee clearance at least 750mm wide x 200 mm deep x 680 mm high; and b) Toe space at least 750mm wide x 230mm deep x 230mm (Figure 6—18).

Figure 6—18: Cantilevered Drinking Fountain (in mm)

6.4.4 Public Pay Telephones

6.4.4.1 All public pay telephones shall have: a) All operable parts (including coin slot) not more than 1200mm above the floor; b) A clear space of 750mm wide by 1200mm deep; c) A minimum of 680mm clear knee space; d) Illumination level of at least 200 lux; and e) A level shelf 450mm wide by 300mm deep, between 720mm to 800mm above the floor,

with a clear space of 250mm above the shelf

6.4.5 Controls

6.4.5.1 All manual controls (light switches, card readers, thermostats, coin slots, control handles, fire alarm pulls, vending machines, etc.) must be: a) Located between 900mm min. and 1200mm max. above the floor;


b) Located with a clear floor space of at least 750mm x 1200mm (clear of door swing.). c) Operable with one hand, without tight grasping, pinching or twisting of the wrist, with a

force not to exceed 22N; and d) Of contrasting color to the background.

6.4.5.2 Push buttons for automatic doors shall have minimum dimensions of 100mm and shall be located such that the opening door does not block them.

6.4.5.3 Information on visual displays shall be supplemented by tactile and/or auditory information.

Figure 6—19: Control Locations (in mm)

6.4.6 Signage

6.4.6.1 Signage indicating room uses, names, or numbers shall: a) Be consistently located, to the latch side of a door, 150mm from the frame; b) Be mounted at a consistent height, such that all characters and symbols are not less than

1200mm above the floor and not more than 1500mm above the floor; c) Have glare‐free surface; d) Have color contrasted to background; e) Be lit to at least 200 lux; and f) Include appropriate pictograms wherever possible (i.e., washrooms, stairs, etc.)

6.4.6.2 Characters on signs shall: a) Be sans serif with Arabic numerals; b) Have a width to height ratio between 3:5 and 1:1 (using an upper case X for character

measurement); c) Have a stroke width to height ratio between 1:5 and 1:10;


d) Be at least 25mm high (for viewing distance of up to 750mm, higher for signs that are to read further away); and

e) Have color contrasted from the background, light colored characters/symbols on a dark background, or dark colored characters/symbols on a light background.

6.4.6.3 Signs that include tactile raised characters (0.8 – 1.5 mm thickness) and Grade 1 Brail, or auditory information shall be provided at identification signs (including building directories, floor designations and room designations), regulatory signs (including identification of building exits) and warning signs (Figure 6—20).

6.4.6.4 Signs incorporating the appropriate symbols for access shall be provided at all barrier‐free facilities such as parking spaces, building entrances, washrooms, showers, elevators, telephones, meeting rooms etc.

6.4.6.5 Provide an audible sign at the main entrance to all buildings to provide information that will assist in way‐finding through the building.

Figure 6—20: Signs

6.4.7 Tactile Warnings

6.4.7.1 Provide tactile warnings (textured surfaces, knurled lever handles etc.) at the following locations: a) Doors to hazardous areas; b) Tops of all stairs and ramps (Figure 6—21 and Figure 6—22); c) Where a barrier‐free walkway crosses a vehicular way; d) The edges of flush pools, planters, etc. that are not protected by curbs (Figure 18A);

I. Be composed of truncated domes;


II. Be slip‐resistant; and III. Have a contrasting color to the surrounding surface.

Figure 6—21: Detectable Warning Indicator Location

Figure 6—22: Tactile Warnings Indicator Location


6.4.7.2 Detectable warning indicators shall be composed of truncated domes and have a contrasting color to the surrounding surface (Figure 6—23).

Figure 6—23: Tactile Warnings & Detectable Warning Indicator

6.4.8 Counters and Line up Guides

6.4.8.1 Provide a section at all service counters (reception, public service, coat checks, etc.) with: a) Clear floor space of 750mm wide by 1200mm deep in front; b) Counter height maximum 860mm above the floor; and c) Clear knee space 1000mm wide by 680mm high.

6.4.8.2 Where line‐up guides are provided, they shall: a) Provide a clear width of at least 1100mm; b) Have a minimum space of 1670mm x 1670mm at changes in direction; c) Be cane‐detectable at or below 680mm above the floor; and d) Be color‐contrasted from the floor.

6.4.9 Places of Assembly

6.4.9.1 For meeting rooms, boardrooms, courtrooms, assembly areas, cafeterias, coffee shops, etc., provide designated space for seating for persons in wheelchairs or scooters as follows:

Total seats provided Minimum designated seating required Up to 100 2 101 ‐ 200 3 201 ‐300 4 301 ‐400 5 401 ‐ 600 6 over 600 1% of seating capacity

Designated spaces shall be on a level surface level (maximum slope in any direction 1%), and at least 840mm wide by 1220 mm deep (front or rear access) or 1525mm deep (side access). Where the seating is fixed, at least one fixed seat directly adjacent to each barrier‐free seating space shall be signed as reserved for companion seating.


Figure 6—24: Wheel Chair Viewing Space

6.4.9.2 Lines of sight must be comparable to other seating and must not be compromised by standing members of the audience.

6.4.9.3 Ensure that tables in areas such as meeting rooms, cafeterias, and libraries are a maximum of 860mm high, and have a clear knee space of at least 750mm wide, 480mm deep, and 680mm high.

6.4.9.4 Aisles such as cafeteria lines, spaces between tables and aisles between Library stacks shall be minimum 915mm wide.

6.4.9.5 Anywhere that coat racks are provided, ensure that at least one section has a rod height not more than 1370mm above the floor.

6.4.10 Assisted Listening Devices

6.4.10.1 Provide an assisted listening device in any auditorium, assembly room, meeting room or theatre with an area greater than 100 s.m. and an occupant load more than 75 people. Such rooms shall be signed with the symbol for persons who are hard of hearing.


6.4.10.2 Any television set displaying information for the public shall include closed captioning.

6.4.11 Visual and Audible Alarms

6.4.11.1 All building alert and alarm signals, including fire alarms, building entrance release hardware and other signals intended for the public to indicate operation of a building access control system shall provide both an audible and a visual signal.

6.4.11.2 Visual alarms shall: a) Have a light intensity of at least 75 Candelas; b) Be located so that at least one is visible from any portion of a floor area; c) Have a flash rate within the frequency range of 1‐3 Hz; and d) Be synchronized to flash in unison wherever multiple alarms may be visible at one time.

6.4.11.3 Where the emergency evacuation planning of a facility necessitates that persons with disabilities await assistance in order to be evacuated (example: floor level above grade served by stairs), provide a safe Area of Refuge in a fire‐separated room, equipped with two‐way communication, emergency lighting, and separate ventilation. This requirement is waived for fully sprinklered buildings.

6.4.12 Life Safety

6.4.12.1 Where a building has an emergency power supply, all automatic doors operators will be provided with emergency power.

6.4.12.2 All facilities shall have an Emergency Policy and Emergency Evacuation Plan that addresses the needs of people with disabilities.

6.4.12.3 All sleeping and living rooms to be provide with audio and visual smoke/carbon dioxide detectors which are hardwired and on a separate circuit.

6.4.13 Cooking & Laundry Facilities

6.4.13.1 Where a building has cooking or laundry facilities, all such facilities will be provided with fixtures and appliances to allow for access for people with disabilities.

6.4.13.2 All laundry facilities shall have a washer and dryer that address the needs of people with disabilities (Figure 6—25).

6.4.13.3 All separate laundry rooms shall have a clear turning area 1500mm to allow for the turning of a wheel chair.

6.4.13.4 All cooking facilities shall have a layout that addresses the needs of people with disabilities (Figure 6—26).

6.4.13.5 All kitchens to have a handicap working area which is at 760mm wide.


Figure 6—25: Washers & Dryers


(c) Figure 6—26: Kitchen Layouts


Figure 6—27: Elevator Clearances


References

• ADA Accessibility Guidelines September 2002

• Bill 125 ‐ Ontarians with Disabilities Act. December 14, 2001

• CAN/CSA B651‐04 Accessible Design for the Built Environment. 2004

• CNIB, Clearing Our Path. August 1998

• GPC Research. Report on Findings: Quantitative Results from On‐Line Barrier‐Free

• Kailes, June Isaacson. Emergency Evacuation Preparedness – A Guide for People with Disabilities and Other Activity Limitations. 2002

• Making Ontario Open for People with Disabilities – A Blueprint for a Strong and Effective Ontarians with Disabilities Act. April 22, 1998

• Management Board Secretariat. Architectural Design Standards for Court Houses. April 1999

• Management Board Secretariat. Barrier‐Free Design Guide for Ontario Government Buildings. 1992

• Ministry of Community and Social Services website, http://www.mcss.gov.on.ca/mcss/english/how/howto_buildings.htm, July 14, 2006.

• Ministry of Municipal Affairs and Housing Provincial Planning and Environmental Services Branch. Handbook on Planning for Barrier‐Free Municipalities (draft).

• Ministry of Municipal Affairs and Housing Technical Advisory Committee. Barrier Free Requirements in the Ontario Building Code: Recommendations for Change. December 2002

• Ministry of Municipal Affairs and Housing, Ontario Building Code 2006, O. Reg. 350/06.

• Ministry of Citizenship, Culture and Recreation. Preventing and Removing Barriers for Ontarians with Disabilities. July 1998

• Holten, Shane. Planning a Barrier‐Free City of Toronto. July 2001.

• Universal Design Institute. Access – A Guide to Accessible Design. 2000.

JUNE 2009 REVISION NO. 02 SURVEYING Standards 7‐1

7 Surveying Standards

7.1 Purpose To provide general reference for surveying procedures performed by and for Libya Housing and Infrastructure Board (HIB). This publication establishes minimum standards, policies, and procedures of surveying for HIB. It provides information on the use of surveying technology to perform surveys for large scale and small scale projects. Accuracy is a prime consideration in surveying and is stressed in this publication.

7.2 Horizontal Control Surveys

7.2.1 Definition A horizontal control survey is performed for the purpose of placing geographic coordinates of latitude and longitude on permanent monuments for referencing lower levels of surveys. A projection is used to place the coordinates on a plane of northing and easting values for simplified measurements. Scale and elevation factors are applied to make the distance measurements applicable to the exact project location on the working surface. If possible, project control should be planned so that project control monuments serve for both horizontal and vertical control. It is important that project control plans consider the need for supplemental control.

7.2.2 Field Methods Particularly for horizontal control surveys, GPS is quickly replacing the use of the total station for long distance traversing. The inherent error of each GPS derived baseline (about 5 mm plus 1 part per 1,000,000) will make accuracy at short distances not so attractive but using baselines of many kilometers suddenly becomes phenomenally accurate and cost effective.

When feasible, horizontal project control shall be established using GPS surveys complying with second‐order accuracy standards. When GPS survey methods cannot be used for all or part of a Horizontal Project Control Survey, a Total Station Survey System (TSSS) traverse network shall be used. The TSSS traverse will comply with second‐order accuracy standards.

Planning the control network so that it will meet the needs of all subsequent project surveys is critical. Key steps in the control planning process are to:

• Ascertain the need for additional corridor control

• Develop a survey work schedule that meets the needs of the Project Development schedule.

• Research the existing horizontal and vertical control networks.

• Recover and evaluate existing control.

• Plan the project control network and select the methods for establishing control.

• Plan supplemental control.


New control stations shall be permanently marked in a manner suitable for the terrain, the design of which shall be agreed with HIB or its representative.

This shall typically be by means of a two centimeter diameter and one meter long iron rod set into at least a half a cubic meter of concrete.

• A station control sheet at a scale of 1:100 will be prepared and a photograph of the station with a small sign indicating the station number in the photograph. An overall control map at a scale commensurate with the project size will indicate the location of all control points for the project.

• Significant nearby topographic features shall be recorded and shown on the station control sheet.

• A minimum of three witness/reference points shall be surveyed from the control station with a bearing and distance to a semi‐permanent object such as a building corner, light standard, sign or other such items.

All monuments set by the surveyor shall be set at sufficient depth to retain a stable and distinctive location and be of sufficient size to withstand the deteriorating forces of nature and shall be of such material that in the surveyor’s judgment will best achieve this goal.

When delineating a right‐of‐way or boundary line as an integral portion of a survey the surveyor shall set, or leave as found, sufficient, stable and reasonably permanent survey markers to represent or reference the property or boundary corners, angle points, and points of curvature or tangency. ALL SURVEY MARKERS SHALL BE SHOWN AND DESCRIBED with sufficient evidence of the location of such markers.

7.2.3 Coordinate Adjustment Control Points set for design and construction projects that are not on‐going at the time of the official publication of this document will be tied to the Libyan Transverse Mercator two‐degree (LTM2°) grid, Libyan Geodetic Datum (LGD) of 2006.

A report showing the WGS 84 geodetic coordinates along with the LGD 2006 geodetic and LTM 2° grid coordinates shall be submitted. The report will show Longitude, Latitude (WGS84 and LGD2006), Ellipsoid Height, North, East (LTM2°), Elevation, Scale Factor, and Surface Adjustment Factor for each point. All Control Description Cards will be obtained from the Survey Department of Libya and will have their official stamp on the card for authentication.

The Surface Adjustment Factor (SAF) allows conversion of grid coordinates to surface coordinates and distances, and vice‐versa.

7.3 Vertical Control Surveys

7.3.1 Definition A vertical control survey is performed for accurately determining the orthometric height (elevation) of permanent monuments to be used as bench marks for lower quality leveling.


Differential leveling is the preferred method of carrying elevations. However, Global Positioning System (GPS) can be used indirectly but with less accuracy. Height measurements from the ellipsoid can be determined very accurately with GPS. Trigonometric leveling, with a total station, is not acceptable for vertical control work.

The use of first order leveling is cost prohibitive and unnecessary in most surveying cases. Discrepancies between originally run level lines in some cases negate the advantages of the precision of the first order and sometimes second order level runs.

The instrument should be treated with care and a peg test should be performed on a regular basis. Level rods are equally critical. All back‐sight and fore‐sight shots should be balanced.

Most digital levels have on‐board adjustment programs and/or a memory card that will allow the data to be transferred to a computer for adjustment. Manual readings can also be hand entered into the data collector to record the data, warn of out‐of‐tolerance readings, adjust the point elevations, and compile reports.

A carefully planned GPS network survey can be used to obtain orthometric heights. Since GPS measures heights from the imaginary ellipsoid surface, the data must be converted to useable orthometric heights through a model of interpolated geoid separation measurements. In order to get the accuracy needed for a vertical control survey, there must be at least 3 or 4 high quality bench marks surrounding the project area (and in 3 or 4 separate quadrants) to better model the area. In other words, at least one bench mark should be fixed in each of the four (4) quadrants of the survey area, such that nearly all of the newly surveyed stations will fall inside a boundary drawn around the outside benchmarks. Additional benchmarks inside the perimeter will aid in strengthening the adjustment. This sometimes makes the use of GPS impractical –differential leveling may be just as cost effective, if the distances are not too great.

7.3.2 GPS Network Design Example: • Roughly locate both new points and existing control on a map showing roads to use in moving

the observers around the project.

• From reconnaissance and mission planning software, determine the best times to observe.

• For each session, draw the independent baselines chosen to be observed on map. Move through the project until all points have been observed.

• Observing the rules for time differences, plan the repeated occupations and observations. Consider redundancy requirements.

• Measure and record antenna height in two different units at the beginning and before the end of each session.

• Fill out observation sheet each session. (See Attachment “A”)

• Every one moves every session (where practical).


In the scope of these specifications, GPS data processing includes the review and cataloging of collected data files, processing phase measurements to determine baseline vectors and/or unknown positions, and performing adjustments and transformations to the processed vectors and positions.

Each step requires quality control analysis, using statistical measures and professional judgment, to achieve the desired level of confidence. Each of these steps is also very dependent upon the measurement technique, the GPS receiver, and antenna types; the observables recorded, and the processing software.

Typically, the elevation basis is either 1.) An existing project (datum specified by project) or 2.) Mean Sea Level. A statement of the basis of elevations shall be made in computer files and placed on all map prints similar to one of the following examples:

1. Elevations refer to a BM set near the N. E. corner of the intersection of Al‐Shutt Street and Gurgi Road (Location), an “X” on top of a concrete wall (description). Elevation is 100.00 meters.

2. Elevations are based upon bench mark A1422, Published elevation—126.042 meters above Mean Sea Level.

7.3.3 Benchmarks Establish benchmarks with physical characteristics and quality commensurate with the order of the leveling survey. Benchmarks should be of a stable, permanent nature; e.g., galvanized steel pipe; steel rod driven into a firm soil base; or cast in place concrete. A brass disk epoxied into a drilled hole in rock or concrete is also acceptable.

Benchmarks should be conveniently located and easily accessible. Whenever possible, benchmarks should be located outside of construction areas, clear of traffic, and within a public right of way.

Space benchmarks as required by project conditions and convenience of operation, generally not to exceed 300 meters apart. Prepare a written benchmark/station description for inclusion in the survey notes and in the project final control report.

A vertical project control survey shall be performed for each specific project that requires elevations to define topographic data points or positions of fixed works. The establishment of vertical project control monuments is important because all subsequent project surveys requiring elevations are to be based on the vertical project control.

Vertical project control surveys shall be based on a single, common vertical datum to ensure that various phases of a project and contiguous projects are consistent.

When feasible, vertical control for projects should be established at all horizontal control stations. Additional benchmarks should be set to densify vertical control to provide convenient control for photogrammetry, topographic, and construction purposes.


7.4 Topographic Surveys

7.4.1 Definition A topographic survey is a survey performed to determine the configuration, relief, or elevations of a portion of the earth’s surface, including the location of natural and/or man made features thereon.

A topographic survey is made for the purpose of gathering relevant information that will be represented on either a topographic map or in a Digital Terrain Model (DTM). Typically, highway planning, engineering design and ROW design are the primary purposes.

A topographic survey is necessary in order to prepare an accurate topographic map and requires the expert skill of a surveyor well versed in maintaining accuracy and precision in detail mapping. A planimetric map is a two dimensional (2D) map that represents the horizontal and vertical positions of the features represented; distinguished from a topographic map by the addition of relief in a measurable form. A topographic map can also be three dimensional that represents the same features as a planimetric map but uses contours or comparable symbols to show mountains, valleys, and plains. A planimetric map is a map that presents the horizontal positions only for the features represented; distinguished from a topographic map by the omission of relief in a measurable form.

7.4.2 Utility Surveys Utility surveys are undertaken to locate existing utilities for (a) consideration in engineering design, (b) purposes of utility relocation, and (c) right‐of‐way acquisition and negotiation. It is important to locate all significant utility facilities.

As a minimum a Topographic Survey shall include the following facilities and critical points:

• Pipeline intersection point with centerlines and/or right of way lines, with size and depth of lines.

o Pipeline vents and markers, angle points, meter vaults, valve pits, etc.

• Water, sanitary and storm sewer line intersection points with size and depths of lines.

o Manholes, valve boxes, meter boxes, crosses, tees, bends, etc. o Elevation on waterlines, sewer inverts, and manhole rims o Fire hydrants and valves

• Roadways

o Curb and gutters and centerline roadway and sidewalks o Utility Poles o Traffic signs and signals o Bridges, headwalls, etc. o Survey control monuments


7.4.3 Digital Terrain Model (DTM) A Digital Terrain Model (DTM) is a mathematical model of a project surface that becomes a three dimensional representation (3D) of existing and proposed ground surface features. Critical calculations and processes based on the DTM include contouring, cross sections and quantities, drainage models, watersheds, hydraulics, water catchment areas, and cross section sheets.

A DTM is created through the construction of a Triangulated Irregular Network (TIN) and is based on modeling the terrain surface as a network of triangular facets that are created by simply connecting each data point to its nearest neighboring points. Each data point (having x, y and z coordinates) is the vertices of two (2) or more triangles. The advantage of the TIN method is its mathematical simplicity‐ all DTM calculations are either linear or planar.

The processes and the resulting DTM offer many advantages over a topographic survey. Field data for a DTM is collected in a way that allows the surveyor to use the latest in automated survey technology. Traditional data collection (for a topographic survey) involves taking cross sections, typically every 30 meters, along a horizontal control line or in a grid pattern. Digital terrain modeling has virtually eliminated this practice. Data points (shots) are taken at every break in elevation with no particular pattern being required. The emphasis is on identifying all features and changes in elevation within project limits. Data is collected using an electronic data collector with an electronic total station. The data points are assigned feature codes, attributes, descriptions, comments, and connectivity linking codes to add intelligence to a point at the time of data entry into data collector.

Information is downloaded from the data collector to a computer, either in the field or later in an office, and is processed.

7.4.4 Route Survey A route survey is an application of the above described topographic or DTM survey along a determined linear ROW route, either existing or proposed, for a utility or roadway.

When this text discusses procedures or standards relating to either a topographic survey or survey for a Digital Terrain Model, the accuracy, standards, equipment and basic procedural methods employed will be the same. A topographic survey will be performed and a DTM can be used for most surveying applications where route design and engineering are required, whereas a topographic map may be better suited for large area site design and development. This specification is intended for use in developing a design survey, a Digital Terrain Model, or a topographic survey, with accuracy sufficient to meet design needs and requirements.

A 3D model or a DTM may be preferred for purposes such as:

• Highway/roadway planning, design

• ROW design

• Drainage studies

• Site development, planning

• Architectural planning, design


• Landscape design.

A significant advantage of a DTM is that it offers the ability to view, inspect, and smoothly navigate through, over and across a DTM in a 3D environment for the purposes of locating, editing, and correcting raw field data (points and chains) in 3D.

7.4.5 Considerations Other Technology A computer model or a DTM is the ultimate work product of any of these newer methods of data acquisition. Depending on the critical factors of each project, including type, terrain, accuracy, precision required, cost, traffic conditions, and safety, such advanced methods may warrant serious consideration as a complement to conventional data gathering or as a replacement of common or conventional surveying methods. While conventional aerial photogrammetry may still be viable, as technology continues to advance, existing methods such as photogrammetry with airborne Global Positioning System (GPS) control becomes more accurate and even more cost effective. Other, newer methods of terrain modeling are also available.

Ground based scanning is an automated collection of data by reflector‐less laser which involves high density scanning of an object or location to collect a “point cloud” of data points. The point cloud of data is further processed into a 3 dimensional computer model image. Typically done from a remote instrument location or multiple locations, 3D Laser scanning is especially good for sites or objects that are difficult to access, have high traffic volumes, involve extreme detail or have other extreme dangers or conditions associated.

This method has also been utilized in place of conventional topographic or digital terrain model (DTM) surveying with much success, especially where high traffic volumes or lane closure issues (safety) were critical factors. Presently the accuracy of the scanned data is said to equal or even exceed that of conventional survey methods, even electronic total station work, with the additional advantage of a greater number of data points all throughout the structure or project. Other methods or technology should be discussed with and approved by HIB or its representative.

7.4.6 Work Product A DTM or Topographic Survey requires:

• A control survey network, with horizontal and vertical positions on primary control points that are monumented, referenced, and placed near or on the project site.

• Points of secondary control, which are based upon and which supplement primary control to facilitate data acquisition within a project.

• A description and location sketch of each control point.

7.4.7 Information Required Information should include the following:

• Project or site location shown on a map

• ROW maps depicting current ROW width(s) and other land, ownership and survey information


• Ownership information of adjacent tracts if available

• Intersecting road ROW information and documentation if available

• Construction plans of existing facilities if available

• Intended use of the survey and required form of deliverable, files required, etc.

• Accuracy required and method of display (contours, spot elevations, etc.)

• Horizontal and vertical datum upon which the survey is be based

• Existing survey control information and data sheets, if available, for horizontal and vertical monumentation

7.4.8 Monuments Reference points and control monuments for a topographic survey may include temporary stakes, hubs, and nails in pavement, iron rods, or reinforced concrete monuments.

A wooden hub or stake, nail or iron rod is considered as secondary control (temporary bench mark or control point) which only supplements primary survey control monumentation to facilitate data acquisition.

Primary control points, whether set by GPS or conventional survey methods, shall be of reasonable permanence and may include concrete monuments.

Monuments whether set or existing shall be well referenced, numbered or named according to procedure, indexed in the project data or field notes and identified in the computer file final deliverable.

Point numbers may be furnished for a monument numbering system. A location sketch and data sheet for each monument should be furnished.

7.4.9 Field Procedures DTM or topographic surveys require a reliable horizontal and vertical control system based on acceptably closed and adjusted traverses and level loops. Attention should be given toward developing this control system before any detail work is begun.

Field work shall be performed to achieve the specified or intended accuracy and results as stated in this publication, in accordance with accepted technical methods, and as directed by the manufacturer of the surveying instrument(s) or equipment used.

Field personnel shall be well trained in the technical aspects of surveying as related to their respective duties.

Surveying instruments shall be checked and kept in close adjustment according to their manufacturer’s specifications or in compliance with textbook standards.


• Electronic distance measuring devices shall be compared against a standardized baseline at 6 month intervals, however a comparison check should always be done as needed, especially if an instrument has been dropped, damaged or is suspect of the same.

• This comparison includes electronic total stations or any other electronic measuring instrument.

• Total stations and theodolites shall be compared against a standard known angle at a 6 month interval; however, a comparison check should always be done as needed, especially if an instrument has been dropped, damaged or is suspect of the same.

• Levels, auto or digital, should be checked by the “2 peg test” or reading the elevation difference between two reference points taken from 1.) A middle setup between points and also 2.) From an end setup. Failure to get the same difference of elevation indicates an out of adjustment condition, which usually requires a shop cleaning and adjustment.

• Auxiliary tapes, cloth or fiberglass, shall only be used for rough measurements where precision is not important, such as determining the width of ditches, the location of excavations or other irregular improvements. Tapes of this sort shall not be used to measure distances in excess of 30 meters.

Field measurements of angles and distances shall be performed in such a manner as to attain the closures and tolerances as found in these standards.

Where aerial photogrammetry is to be used to compile the topographic map, the surveyor shall consult with the photogrammetrist as to specific requirements for the photo control and for additional supplemental information required by conditions of a specific project or location.

• Horizontal and vertical photo control (picture points) shall be based on and looped to the control system.

• Identification of photo control (picture points) must be precise and clear since these points will be used to build the network from which the photogrammetrist must work.

• Photo control points, set before the aerial photography is made, shall be located from, and looped to the control system. The density and pattern for paneled picture points shall be determined through consultation and coordination with the photogrammetrist.

For these purposes, methods that are more modern are normally used, such as the DTM survey that incorporate methods described in the section below.

Surveying procedures with electronic total station or with GPS shall incorporate control points that are tied to a primary control system network of an appropriate level of precision and accuracy for the project.

Acquisition of field data may require running secondary control and bench marks that begin and end at points on the primary control system.

The use of open ended legs or “spur” lines should be avoided whenever possible. When such lines are necessary, appropriate checks shall be made on all field data before leaving the vicinity.


Any field notes written in a field book shall be kept in a neat and orderly manner on all control points, primary or secondary. Appropriate annotations on location, description of point and reference to identifying specific features located during the DTM or topographic survey shall be made.

7.4.10 Topographic Features The perimeter limits of any unique or special features such as historic structures, cemeteries, burial grounds or gravesites known or found within the project limits, or adjacent to it, and which may be affected (by the existing or proposed ROW ), shall be shown by actual location.

Buildings and improvements, including distance from proposed ROW up to 15 meters. The project manager may require extending this distance.

Items to be located as a minimum are as follows:

• Center lines and top of banks of dry creeks, streams or other confined intermittent watercourses

• Paths, car trails, pasture roads, etc.

• Additional data points outside of the ROW, as required and directed by client.

• Creeks, streams, rivers and water bodies, shown and identified by name if available. Water levels shall be determined and displayed by elevation.

• Drainage areas ‐ field information on drainage area(s) of a project shall be collected in the same manner as other information to the extent as directed by the project manager and/or client.

• Utilities as mentioned in Utility Surveys (3.2), above.

7.4.11 Electronic Data In nearly all cases, field work is automated by the use of computer software and hardware for collecting, reviewing, editing, and processing field data. A data collector may be connected to the instrument (total station, GPS receiver, digital level, etc.) to store the raw measurement data and perform coordinated geometry (COGO) functions while in the field. Original raw data must be saved as a file for retention, as a matter of record, before any data editing or processing is done.

7.4.12 Data Collection Field data in electronic form will be collected. Its purpose is to provide a more flexible and user definable method of recording horizontal angle, vertical angle and slope distance from most of the total stations and in a standard format recognized by good surveying methods. A standard Field Book will include the date, weather, crew, job name and job number, plus a description of the work being performed. It will also be used to record pertinent field information in an accurate, clear format.

There are numerous ways to provide connectivity. When performing radial topography surveys for a DTM, points in the same break‐line such as edge of pavement, centerlines and ditch lines can be linked together. These survey chains can ultimately be imported to mapping files or to DTM files as DTM break lines.


The contractor will submit their Feature Codes and Cells for use in the field to insure standardization of line weight, color, levels, and symbology. The feature codes also determine where the points and chains will go, either to a mapping file or a DTM file. Topographic surveys, traverses, and level runs may be collected in approved software that can then be reduced to coordinates on a desktop PC.

7.5 Construction Staking

7.5.1 Field Methods Methods used to establish construction stakes are at the surveyor’s option. These methods may include any means capable of maintaining the necessary tolerances. The surveyor is responsible to provide additional control stakes and verification of existing control and to maintain them during the construction process.

Sufficient independent field checks will be made at the discretion of the surveyor to assure the integrity of the stakes. The integrity of stakeout set‐up points should be verified before use by taking check shots on other control points. All positions staked in the field should be checked against the computed positions and the results recorded in electronic stakeout reports and/or on stakeout listings.

Working stakes used by the surveyor in actually performing the work are the surveyor’s responsibility and are to be set by the surveyor.

7.6 AsBuilt Surveys

7.6.1 Definition As‐built Surveys (or post construction surveys), show the conditions of the construction project after the construction is completed.

Features shown on the as‐built survey must be surveyed after construction.

7.6.2 Deliverable As‐Built drawings shall include, as a minimum, revisions to alignments and right‐of‐way, grade revisions, drainage changes, changes to roadway features and revisions on the location of utility crossings and irrigation crossovers. The As‐Built drawings will be translated to the Libyan Transverse Mercator two‐degree (LTM2°) grid, Libyan Geodetic Datum (LGD) of 2006, through a report translating from the datum used on the project to LGD 2006 datum. This report will show the Longitude, Latitude (WGS84 and LGD2006), Ellipsoid Height, North grid coordinate, East grid coordinate (LTM2°), Elevation, Scale Factor and Surface Adjustment Factor for each control point.

After construction is complete, the as‐built corrections will be placed on a copy of the Cadd files. Each as‐built sheet will be clearly marked as an AS‐BUILT SURVEY.

7.7 Survey Map Check List The following Check List is a minimum amount of information to be placed on a standard map or maps. It is imperative to have quality maps with pertinent information on them.

• Company name, address, telephone number, e‐mail address and fax number


• Client name, address, telephone number, e‐mail address and fax number

• Scale and Bar Scale

• Date

• North arrow

• Title Block

• Description of survey

• Legend

• Limits of Survey

• Existing and new control

• Coordinate basis

• Signature of surveyor (if required)

• Notes

• Sheet numbers

• Control coordinates and elevations

• Border

• Vicinity Map


ATTACHMENT 7A

GPS LOG SHEET

Project Name ______________________________________________

Operator Name

Observation Date

Station Name

Antenna Height 1st measurement

Meters 2nd measurement

Survey feet 3rd measurement

Average

Measure to: Bottom of notch Top of notch Antenna ref. point

Antenna Type

Actual start time

Actual stop time

4 digit receiver number

NOTES:

JUNE 2009 REVISION NO. 02 ROADWAY 8‐1

8 Roadway

8.1 Highway Systems

8.1.1 Functional Classification Functional classification is defined as the process by which streets and highways are grouped into systems according to the character of service they are intended to provide. Each roadway classification has a distinct function, character, and level of access control, as shown in Table .

Table 8‐1. Functional System Characteristics

Functional System General Description

Freeway Provides the highest level of service at the highest speed for the longest uninterrupted distance Full access control using only grade‐separated interchanges

Expressway Provides high speed and long distances traveled by vehicles Full access control by grade‐separated interchanges Service roads normally provided to serve lands adjacent to the highway, connected to the expressway mainline by free‐flowing ramps

Arterial Provides moderate distances for traffic and with lower design standards than expressways Access generally by means of at‐grade intersections (signalized or roundabout), but may also use grade‐separated interchanges

Collector Collects traffic from locals and channels it into the arterial systems Provides both land access and traffic circulation with residential neighborhoods, commercial, and industrial areas Intended for low speeds and minimal access control Although used for through traffic, access to adjacent land is very important

Local Intended for short distances only with low speed Provides access to residential and commercial facilities Provides access to higher systems

The following sections briefly introduce each of the classes:

8.1.2 Freeways A freeway is a road which is designed to move heavy volumes of high speed traffic under free flowing conditions. The need for a freeway is generated by high traffic volumes which in turn necessitates fully controlled access. In rural areas, the freeway connects major cities or industrial areas. In urban areas, the freeway provides high‐standard routes connecting areas of major traffic generation.

8.1.3 Expressways An expressway is similar to a freeway in its basic function except that it does not require the fully controlled access. Access may be fully or partially controlled by grade‐separated interchanges, and can have connections to Service Roads that provide access to local roads.


8.1.4 Arterials Arterial roads are of a lower design standard than freeways and expressways. Their intersections with other arterials and lower‐class roads are generally at grade, and controlled by fixed signing or traffic signals. Arterials are intended to carry large volumes of traffic moving at medium to high speed, and are used by a broad range of vehicle types, because they distribute traffic from the higher classes to the lower classes and vice versa. Arterial roads can also be identified as Service Roads since they run parallel and are connected to the expressways to provide access to local traffic.

8.1.5 Collectors The function of these roads is to collect traffic flow from the local roads to the arterial roads and to distribute traffic flow from arterials back to the local roads. Access to properties is normally allowed on collector roads. In rural areas, the function of collector is twofold; to provide access to adjacent land uses and to carry traffic into areas with sparse development.

8.1.6 Local Roads Local roads are designated to allow vehicles to reach the frontage of properties from a collector road or arterial road. Their main function is to provide land access, and they generally carry low volumes of traffic. They serve residential, commercial, or industrial land uses. As this is the lowest class in the road hierarchy, direct access is permitted to all abutting properties.

8.2 Traffic

8.2.1 Level of Service The average highway user will tolerate a certain level of congestion and delay before he becomes frustrated or attempts unsafe driving maneuvers. This level will vary according to the type of facility. To characterize acceptable degrees of congestion, the level‐of‐service concept has been developed. The application of level of service involves choosing the appropriate level for the selected design year. The Level of Service is graded from A to F, where level A is the highest and level F is the lowest. Table 8‐2 gives general guidelines for use in selecting the level of service. Table 8‐3 gives the general definitions of these levels of service.

Table 8‐1. Minimum Level of Service Guidelines

Highway Type

Type of Area and Level of Service

Rural Level

Rural Rolling

Rural Mountainous

Urban and Suburban

Freeway B B C C

Expressway B B C C

Arterial B B C C

Collector C C D D

Local D D D D


Table 8—2. General Definitions of Levels of Service

Level of Service General Operating Condition

A Free flow

B Reasonably free flow

C Stable flow

D Approaching unstable flow

E Unstable flow

F Forced or breakdown flow

The at‐grade intersection should operate at no more than one level of service below the values in Table 8‐1. Capacity of signalized intersections depends on many factors, including:

1. Intersection geometry including the number and width of lanes, grades, and land use.

1. Percentage of heavy vehicles

2. Location of and use of bus stops

3. Distribution of vehicles by movement (left, thru, right)

4. Pedestrian‐crossing flows

5. Peak‐hour factor

6. Signal phasing, turning and type of control at each approach

8.2.2 Design Vehicles The characteristics of vehicles using the highway are important controls in geometric design. These will vary according to the type of vehicle being considered. When a highway facility or intersection is under design, the largest design vehicle likely to use that facility with considerable frequency should be used to determine the selected design values. Typically, trucks have the greater influence on design. Table 8 presents basic information on dimensions for the standard design vehicles.

Table 8‐4. Design Vehicle Parameters (meters)

Design Vehicle Type Symbol* Height Width Length Min. Design Turning Radius

Min. Inside Radius

Passenger Car P 2.0 2.2 5.8 7.3 4.4

Single Unit Truck SU 4.1 2.6 9.1 12.8 8.6

Single Unit Bus BUS 4.1 2.6 12.1 12.8 7.5


Design Vehicle Type Symbol* Height Width Length Min. Design Turning Radius

Min. Inside Radius

Articulated Bus A‐Bus 3.4 2.6 18.3 12.1 6.5

Intermediate Semi‐Trailer WB‐12 4.1 2.6 15.2 12.2 5.9

Semi‐Trailer Combination Large

WB‐15 4.1 2.6 16.7 13.7 5.2

Semi‐Trailer Full Trailer Combination

WB‐18 4.1 2.6 19.9 13.7 6.8

Inter‐State Semi‐Trailer WB‐19 4.1 2.6 21.0 13.7 2.8

Inter‐State Semi‐Trailer WB‐20 4.1 2.6 22.5 13.7 1.3

Triple Semi‐Trailer WB‐29 4.1 2.6 31.0 15.2 6.3

Turnpike Double Semi‐Trailer

WB‐35 4.1 2.6 35.9 18.3 5.2

Motor Home MH 3.7 2.4 9.2 12.2 7.9

Passenger Car with Trailer P/T 3.1 2.4 14.9 10.1 5.3

Passenger Car with Boat Trailer

P/B ‐ 2.4 12.8 7.3 2.4

Motor Home with Boat Trailer

MH/B 3.7 2.4 16.2 15.2 10.7

*The designation WB relates to approximate wheelbase; WB‐12 denotes a truck whose wheelbase is around 12m.

8.3 Speed The highway should be designed to accommodate the speed desires of most highway users, within the limits of safety.

8.3.1 Design Speed Design speed is the maximum safe speed that can be maintained over a specified section of highway when conditions are so favorable that the design features of the highway govern. Factors that influence the design speed include roadway classification, urban and rural areas, economic matters, and the terrain. Many design elements such as horizontal and vertical curvature, superelevation, and sight distances, are directly dependent on the design speed. Table 8 provides recommended design speeds for varying conditions.


Table 8‐5. Design Speeds

Roadway Classification

Design Speed (km/h)

Rural Roads Urban Roads Absolute Minimum (Only in Mountainous Terrain) Min. Max. Min. Max.

Freeway 120 140 100 120 80

Expressway 100 120 80 120 80

Arterial 80 100 60 100 50

Collector 60 80 50 80 50

Local 40 60 30 60 30

8.3.2 Posted Speed The posted speed provides a factor of safety for those drivers who tend to drive faster than the speed limit but are still within the design speed. The posted speeds are mandatory to limit the speed of those fast drivers and provide safe driving condition. Table 8—6 indicates the posted speed which is appropriate for a given design speed.

Table 8—6. Recommended Posted Speeds

Design Speed (km/h) Posted Speed (km/h)

30 – 40 30 – 40 50 40 60 50 70 60 80 70 90 80 100 90 120 100 140 120

Local Roads and Streets should have a Posted Speed of 50 km/h or lower as local conditions dictate such as near school zones.

8.3.3 Ramps The ramps within a grade‐separated interchanges typically have a lower design speed than that of a mainline. Table 8—7 should be used as the minimum design speed.


Table 8—7. Minimum Design Speed for Connecting Roadways

Mainline Design Speed (km/h)

Minimum Design Speed for Connecting Roadway (km/h)

Ramps Loops 50 30 20 60 40 30 70 50 40 80 60 40 90 60 50 100 70 50 120 80 60 140 90 70

8.4 Sight Distance Sight distance values affect the design of horizontal and vertical alignment, at‐grade intersections, interchanges, and highway crossings. Types of sight distance (stopping, decision, or passing) depend on the type of highway and potential hazard. On horizontal curves, sight distance is most critical on the inside of a curve. Roadside objects on the inside of a curve are required to be set back from the edge of the traveled way by a greater distance than that of a straight line. On vertical curves, sight distance is typically controlled by the eye and object heights.

8.4.1 Stopping Sight Distance (SSD) Stopping sight distance is the sum of two distances: the distance traveled during driver perception/reaction time, and the distance traveled during brake application. The perception/reaction time is usually 2.5 sec.

Perception/Reaction Distance is calculated by:

PRD = 0.278tV

Where: PRD = perception/reaction distance (m) t = perception time + reaction time (sec) V = initial speed (km/h)

Braking Distance is calculated by:

BD = V²/254(f ± G)

Where: BD = braking distance (m) V = initial speed (km/h) f = coefficient of friction G = grade (%) divided by 100

When determining stopping sight distances, the following should be applied for eye and object heights:

• Driver’s eye height 1.05m to 2.40m

• Object height 0.15m to 2.00m


Figure 8‐1. Visibility Envelope for Stopping Sight Distance

Table 8‐8 summarizes the rounded stopping sight distance values for design.

Table 8‐8. Stopping Sight Distances

Design Speed (km/h)

Friction Coefficient (f)

Stopping Sight Distance (m)

Level* Downgrade Upgrade

3% 6% 9% 3% 6% 9%

30 0.40 35 32 35 35 31 30 29

40 0.38 50 50 50 53 45 44 43

50 0.35 65 66 70 74 61 59 58

60 0.33 85 87 92 97 80 77 75

70 0.31 105 110 116 124 100 97 93

80 0.30 130 136 144 154 123 118 114

90 0.30 160 164 174 187 148 141 136

100 0.29 185 194 207 223 174 167 160

120 0.28 250 263 281 304 234 223 214

* Values are also included in the Design Controls for Crest and Sag Vertical Curves, Error! Reference source not found..

8.4.2 Passing Sight Distance (PSD) Passing sight distance applies to undivided two‐way, two‐lane roads, in which a driver passes another vehicle without interfering with an oncoming vehicle that appears when the passing vehicle begins its maneuver. The visibility envelope for the Passing Sight Distance is based on:


• Driver’s eye height 1.05m to 2.40m


Table 8‐9 provides the passing sight distance for various design speeds.

Table 8‐9. Passing Sight Distances

Design Speed (km/h) Minimum Passing Sight Distance (m)

30 200

40 270

50 345

60 410

70 485

80 540

90 615

100 670

8.4.3 Decision Sight Distance Decision sight distance is the distance required for a driver to detect an unexpected or otherwise difficult‐to‐perceive information source or hazard in a roadway environment that may be visually cluttered, recognize the hazard or its threat potential, select an appropriate speed and path, and initiate and complete the required safety maneuver safely and efficiently.

Decision sight distance, as with stopping sight distance, is the sum of perception/reaction time and vehicle maneuver time (stopping or a lane change). The application of decision sight distance must be individually assessed at each location. The visibility envelope for Decision Sight Distance is the same as for Stopping Sight Distance, namely:

• Driver’s eye‐height 1.05m to 2.40m



Table 8 provides the necessary information to determine the required distance.

Table 8‐10. Decision Sight Distance

Design Speed (km/h)

Design Sight Distance (m)

Stop Maneuver All Other Maneuvers

Rural Urban Rural Urban

50 75 160 145 200

60 95 205 175 235

70 125 250 200 275

80 155 300 230 315

90 185 360 275 360

100 225 415 315 405

120 305 505 375 470

8.5 Horizontal Alignment

8.5.1 General Horizontal alignment should be designed to provide a continuous, uniform, and safe driving condition and speed for vehicles. It should meet the following general considerations:

• Horizontal alignment should be as smooth as possible and in harmony with the topography. Flatter curvature with shorter tangents is generally preferable to sharp curves connected by long tangents. Angle points should be avoided.

• The minimum length of horizontal curves should be:

Lmin = 6V (high speed freeways)

Lmin = 3V (other arterials)

Where V = design speed (km/h)

• Broken‐back curves (short tangent between two curves in same direction) should be avoided.

• Compound curves should be avoided where possible. Where they are used, the radius of the flatter curve should not be more than 50% greater than the radius of the sharper curve. However, this consideration does not necessarily apply at intersections and roundabouts, where lower speeds pertain.

• Reverse circular curves on high‐speed roads should include a transition section of sufficient length to accommodate the reversal of superelevation between the circular curves.


• The horizontal alignment should be in balance with the vertical alignment and consistent with other design features.

• Horizontal curves should be avoided on bridges whenever possible. They cause design, construction, and operational problems. Where a curve is necessary on a bridge, a simple curve should be used on the bridge and any curvature or superelevation transitions placed on the approaching roadway.

Factors that influence the degree of horizontal curvature of a road include:

• Safety

• Design speed

• Topography, adjacent land use and obstructions

• Vertical alignment

• Maximum allowable superelevation

• Roadway classification

• Cost

8.5.2 Types of Horizontal Curvature

8.5.2.1 Simple Curves A simple curve has a constant circular radius which achieves the desired deflection without using an entering or exiting transition. Because of their simplicity and ease of design, survey, and construction, this is the most frequently used curve. Figure 8‐2 illustrates a simple curve layout.


Figure 8‐2. Simple Curve

8.5.2.2 Compound Curves Compound curves are used to transition into and from a simple curve. Compound curves are appropriate for intersection curb radii, ramps, and transitions into sharper curves. As the curvature


becomes successively sharper, the radius of the flatter circular curve should not be more than 50% greater than that of the sharper curve. Figures 8‐3 and 8‐4 illustrate a typical compound curve layout and warrants for compound curvature.

Figure 8‐3. Compound Curve


Figure 8‐4. Compound Curve Transition

8.5.3 Minimum Curvature There is a direct relationship between the vehicle speed, the radius of the curve, the superelevation, and the side friction between the tire and the road surface.


Where R = radius of curve (m) V = vehicle speed (km/h) e = superelevation (%) divided by 100 fs = side friction factor

The side friction factor ranges from 0.35 to 0.50 on dry roads and on wet surfaces it may drop to around 0.2. Table 8‐11 provides the minimum radii for varying design speeds and a range of superelevation rates.

Table 8‐11. Minimum Horizontal Curvature

Design Speed (km/h)

Minimum Radius (m)

Normal Crown ‐2%

Maximum Superelevation (e)

2% 4% 6% 8%

30 50 40 35 30 30

40 90 70 60 55 50

50 140 110 100 90 80

60 200 165 150 135 120

70 300 230 215 195 170

80 430 320 280 250 230

90 570 420 375 335 305

100 750 545 490 435 400

120 1220 850 810 755 670

140 1930 1290 1100 965 870

Superelevation is limited to 2%

8.5.4 Spiral Curve Transition Spiral transition curves improve the appearance of the alignment and assist in the introduction of superelevation prior to the circular curve. A properly designed transition curve provides a natural, easy‐to‐follow path for drivers and minimizes encroachment on adjoining traffic lanes. It provides flexibility in accomplishing the widening of sharp curves. For the Euler spiral (or clothoid), the degree of curvature varies directly with the length along the curve. Figure 8‐5 shows the layout of a typical transition curve joining a tangent to a circular curve.


Figure 8‐5. Typical Spiral Transition Curve

The length of the transition curve (TS to SC in Figure 8‐5) depends on the radius of the circular curve into which it leads. It is defined by the following formula:

Where Ls = length of spiral (m)

V = design speed (km/h) q = rate of change of centripetal acceleration (m/s³) R = radius of circular curve (m)

The value of q = 0.3 m/s³ is desirable. Table 8‐12 gives rounded values of the computed spiral lengths of the radii for e = 6% in Table 8‐11.

Table 8‐12. Spiral Lengths for Minimum Radii at 6% Superelevation

Design Speed (km/h)

Minimum Radius e = 6%

Length of Spiral

Desirable Minimum

60 135 115 60

70 195 130 65

80 250 145 75

90 335 155 80

100 435 170 85

120 755 190 95

140 965 205 100


8.5.5 Horizontal Stopping Sight Distance Safe sight distance must be provided on the inside of horizontal curves. Obstructions that interfere with the needed sight distance should be removed, if possible. On horizontal curves, a designer must provide a “middle ordinate” between the center of the inside lane and the sight obstruction. The basic equation is:

.

Where: M = middle ordinate, or distance from the center of the inside lane to the obstruction (m). R = radius of curve (m) S = stopping sight distance (m)

The height of eye is 1080 millimeters and the height of object is 600 millimeters. The line‐of‐sight intercept with the view obstruction is at the midpoint of the sight line and 840 millimeters above the center of the inside lane. See Figure 8‐6.

Figure 8‐6. Components for Determining Horizontal Sight Distance

8.5.6 Superelevation Superelevation counterbalances the centrifugal force, or outward pull, of a vehicle traversing a horizontal curve. This outward pull can be counterbalanced by the roadway being superelevated, the side friction developed between tires and surface, or some combination of the two. This allows a vehicle to travel at higher speeds around the horizontal curves.


8.5.6.1 Superelevation Rates The maximum useable rate for superelevation (emax) is controlled by several factors: Climate conditions, terrain conditions, type of area, and the frequency of slow moving vehicles. The maximum rates of superelevation based on roadway classifications are shown in Table 8‐13.

Table 8‐13. Maximum Superelevation

Roadway Classification Max. Superelevation

(emax)

Local 4%

Collector 4% (urban) 6% (rural)

Arterial 4% (urban) 8% (rural)

Expressway and Freeway 8%

Loops within Interchanges 8%

8.5.6.2 Superelevation Transition A length of superelevation transition shall be required to accomplish the change in cross slope from a normal crown section to a fully superelevated section or vice versa. The length of superelevation transition shall consist of a tangent runout and a superelevation runoff.

Tangent Runout: is the length of highway needed to accomplish the change in cross slope from a normal cross section to a section with the adverse crown removed (0%), or vice versa.

Superelevation Runoff: is the length of highway needed to accomplish the change in cross slope from a section with the adverse crown removed (0%) to a fully superelevated section, or vice versa.

The length for superelevation runoff is dependent on the width of the pavement and the change in superelevation over the transitional length, and is defined by the following formula:

L = 2 x W x ∆e

Where L = superelevation runoff length (m) W = pavement width (m) ∆e = algebraic difference in superelevation (%)

Superelevation runoff lengths should be long enough so that the rate of change of the edges of pavement relative to the centerline does not exceed empirically developed controls. These maximum relative gradients, which provide a minimum length of runoff, are given in Table 8‐14.


Table 8‐14. Maximum Relative Gradients

Design Speed (km/h)

Maximum Relative Gradient (%) Equivalent Maximum

Relative Slope

30 0.75 1:133

40 0.70 1:143

50 0.65 1:154

60 0.60 1:167

70 0.55 1:182

80 0.50 1:200

90 0.47 1:213

100 0.44 1:227

120 0.38 1:263

The pavement may be rotated about the centerline or either edge of the travel lanes. Figure 8‐7 shows typical methods of developing superelevation by rotating about the edges and about the center of the road.


Figure 8‐7. Development of Superelevation


8.5.6.3 Design Considerations 2. Superelevation is introduced or removed uniformly over the lengths required for comfort

and safety.

7. Place approximately two‐thirds of the runoff on the tangent section and one‐third on the horizontal curve.

8. On compound curves, full superelevation for the sharpest curve should be attained at the PCC.

9. For compound curves also, if the flatter entering curve is less than or equal to 150 m, a uniform longitudinal gradient should be used throughout the transition. If the flatter entering curve is longer than 150 m, it may be preferable to consider the two curves separately. Superelevation for the entering curve would be developed by the 2/3rd‐1/3rd distribution method. This rate would be maintained until it is necessary to develop the remaining superelevation for the sharper curve.

10. When spiral transitions are used, the adverse crown is completely removed at the beginning of the spiral. The tangent runout length occurs prior to the beginning of the spiral transition. The rate of transition used in the tangent runout should be the same rate used for the superelevation runoff.

11. For the spiral transitions, the transition for the superelevation runoff will be applied over the entire length of spiral, with full superelevation developed at the horizontal curves’ PSC.

12. The minimum superelevation runoff lengths for roadways wider than two lanes should be as follows:

(a) Three-lane traveled ways; 1.2 times the corresponding length for two-lane traveled ways.

(b) Four-lane undivided traveled ways; 1.5 times the corresponding length for two-lane highways.

(c) Six-lane undivided traveled ways; 2.0 times the corresponding length for two-lane traveled ways.

8.5.6.4 Shoulder Superelevation All outside shoulders and median shoulders of 1.25 meter or greater should slope away from the travel lanes on superelevated curves. The maximum algebraic difference between the travel lanes slope and shoulder slope is 0.09 m/m. Shoulders less than 1.25 meters should slope in the same direction as the travel lane; see Figure 8‐8.


Figure 8‐8. Highway with Paved Shoulders

8.5.7 Minimum Lane Width on Curves Because the rear wheels of vehicles do not exactly follow the track of the front wheels, it is necessary to widen the pavement on low radius curves. Widening is dependent on vehicle geometry (wheelbase), lane width and curve radius. Widening should be applied in both directions of travel to produce the lane width of the circular curve as shown in Table 8‐15.

Table 8‐15. Minimum Lane Width on Curves

Radius (m) Lane Width (m)

125 – 300 4.5

300 – 400 4.0

More than 400 Normal width


8.6 Vertical Alignment The highway vertical alignment is controlled by: Topography, traffic volumes and operating characteristics, highway classification, safety, sight distance, design speed, horizontal alignment, drainage, access to adjacent properties and cost. Where a highway crosses a waterway, the vertical profile of the highway must be consistent with the design flood frequency.

8.6.1 Grades Table 8‐16 presents the recommended desirable and maximum highway grades. Flatter grades should be used where possible. On a long ascending grade it is preferable to place the steepest grade at the bottom and flatten the grade near the top.

Table 8‐16. Recommended Maximum Grades

At grade‐separated interchanges, the maximum grade for the on and off ramps may be up to 2% greater than the corresponding maximum grade permitted on the mainline.

FUNCTIONALCLASSIFICATION U/R TERRAIN 30 40 50 60 70 80 90 100 110 120

LEVEL .. .. .. .. .. 4 4 3 3 3

ROLLING .. .. .. .. .. 5 5 5 4 4

FREEWAY/ URBAN MOUNTAINOUS .. .. .. .. .. 6 6 6 5 ..

EXPRESSWAY LEVEL .. .. .. .. .. 4 4 3 3 3

ROLLING .. .. .. .. .. 5 5 5 4 4

RURAL MOUNTAINOUS .. .. .. .. .. 6 6 6 5 ..

LEVEL .. .. 8 7 6 6 5 5 .. ..

ROLLING .. .. 9 8 7 7 6 6 .. ..

ARTERIAL URBAN MOUNTAINOUS .. .. 11 10 9 9 8 8 .. ..

LEVEL .. .. .. 5 5 4 4 3 3 3

ROLLING .. .. .. 6 6 5 5 4 4 4

RURAL MOUNTAINOUS .. .. .. 8 7 6 6 6 5 5

LEVEL 9 9 9 9 8 7 7 7 5 ..

ROLLING 12 12 11 10 9 8 8 8 6 ..

COLLECTOR URBAN MOUNTAINOUS 14 13 12 12 11 10 10 10 7 ..

LEVEL 7 7 7 7 7 6 6 5 4 ..

ROLLING 10 10 9 8 8 7 7 6 5 ..

RURAL MOUNTAINOUS 12 11 10 10 10 9 9 8 6 ..

LEVEL

ROLLING

LOCAL URBAN MOUNTAINOUS

LEVEL 8 7 7 7 7 6 6 5 .. ..

ROLLING 11 11 10 10 9 8 7 6 .. ..

RURAL MOUNTAINOUS 16 15 14 13 12 10 10 .. .. ..

GRADE MAY BE 1% STEEPER THAN TABLE VALUES. FOR LOW ‐VOLUME RURAL HIGHWAYS,

DESIGN SPEED (KM/H)

SEE NOTE 4

ab e 8 6 CO U G S

Notes: 1. FOR GRADES OF LENGTH LESS THAN 150 m AND FOR 1‐WAY DOWN GRADES, THE MAXIMUM

4. GRADES SHOULD BE AS FLAT AS IS CONSISTENT WITH THE SORROUNDING TERRAIN AND LAND USE IN THE AREA.

IN RESIDENTIAL AREAS,THE MAXIMUM GRADE SHOULD BE 15% IN COMMERCIAL AND INDUSTRIAL AREAS

WHERE TRUCK USE IS EXPECTED, THE MAXIMUM GRADE SHOULD BE 8% AND DESIRABLY 5%.

GRADES MAY BE 2% STEEPER.

2. IN URBAN AREAS, GRADES 1% STEEPER MAY BE USED FOR EXTREME CASES WHERE (A) EXISTING DEVELOPMENT

PRECLUDES USING FLATTER GRADES, OR (B) 1‐WAY DOWN GRADES IN LEVEL OR ROLLING TERRAIN.

3. GRADES SHOWN FOR RURAL AND URBAN CONDITIONS OF SHORT LENGTH, (LESS THAN 150 m), ON 1‐WAY

DOWN GRADES AND ON LOW‐VOLUME RURAL COLLECTORS MAY BE 2% STEEPER.


In addition to the maximum grade, the designer must consider the length of the grade. The gradient in combination with its length will determine the truck speed reduction on upgrades. The guidelines given in Table 8‐17 for the maximum length of sustained grade are based on a speed reduction for trucks of 15 km/h.

Table 8‐17. Critical Grade Lengths

% Upgrade Max. Length of Grade

(m)

2 650

3 400

4 280

5 210

6 175

7 150

8 and more 130

Minimum Grade

The minimum longitudinal grades for proper drainage are:

• 0.3% for Freeways, Expressways and Arterials

• 0.2% for Collectors and Local Roads

8.6.2 Vertical Curves Vertical curves are provided at all changes in grade, except as shown in the following Table 8‐18:

Table 8‐18. Maximum Change in Grade without Vertical Curves

The curvature and length of vertical curves shall be such that the required sight distances are met. Design controls for the vertical curves are generally based on the following formula, where K implies the rate of curvature and it is a good indication for proper drainage:

K = L/A

Where L = length of curve (m) A = algebraic difference in grades (%)

Computations for vertical curves are shown in Figures 8‐9, 8‐10 and 8‐11.

DESIGN SPEED (KM/H) 50 60 70 80 90 100 110

MAXIMUM CHANGE INGRADE IN PERCENT 1.00 0.80 0.70 0.60 0.40 0.30 0.20

g


Figure 8‐9. Parabolic Vertical Curves (a)


Figure 8‐10. Parabolic Vertical Curves (b)


Figure 8‐11. Parabolic Vertical Curves (c)


The primary control for crest vertical curves is providing adequate stopping sight distance. The primary control for sag vertical curves is the headlight sight distance, where the height of the headlights is assumed to be 600 millimeters.

Table 8‐19 shows the minimum K values for design as required for the range of values of stopping sight distances for each design speed.

Table 8‐19. Design Controls for Crest and Sag Vertical Curves

Design Speed (km/h)

Stopping Sight Distance(m)

Rate of Vertical Curvature, K

Crest Curves Sag Curves

30 35 2 6

40 50 4 9

50 65 7 13

60 85 11 18

70 105 17 23

80 130 26 30

90 160 39 38

100 185 52 45

120 250 95 63

8.6.3 Combining Horizontal and Vertical Alignments To obtain an adequate alignment it is important to integrate the vertical and horizontal geometry, and to consider the road as a three‐dimensional unit. A summary of desirable and undesirable combinations of alignments is provided in Figure 8‐12 and Figure 8‐13.


Figure 8‐12. Summary of Undesirable Alignment Combinations


Figure 8‐13. Summary of Desirable Alignment Combinations

8.6.4 Vertical Clearances Minimum vertical clearances are needed at all overhead structures including bridges, overhead signs and cables, overhead traffic lights and suspended lighting. The minimum clearance for new construction is 5.5 m. This clearance includes up to 200 mm for pavement overlay, which may be applied during the road maintenance, resulting in a clearance of 5.3 m that must be maintained at all times.

Where a road passing underneath the bridge is on a sag curve, the headroom needs to be increased to allow for the limiting effect of the sag. Table 8‐20 provides the additional headroom values.

Table 8‐20. Additional Clearance for Sag Curves

Sag K Value Additional

Headroom (m)

4 and 5 0.12

6 and 7 0.08

8 and 9 0.06

10 to 12 0.05

13 to 17 0.04

18 to 25 0.03

26 to 50 0.02

51 to 100 0.01

8.7 Cross Section Elements

8.7.1 General The limits of the road cross section are governed by the width of the right‐of‐way available, which is typically determined at the planning stage. Many factors affect and determine the roadway typical


section such as: design speed, roadway classification, right‐of‐way, traffic volume, environmental issues, existing or proposed utilities, bikers, and so many others.

The basic elements of a roadway cross section are:

• Right‐of‐way limits

• Borders

• Drainage Ditches

• Side slopes

• Sidewalks

• Curbing

• Shoulders

• Travel Lanes

• Cross Slopes

• Medians

• Horizontal Clearances

• Others:

- Service Roads

- Auxiliary Lanes

- Bridges

- Tunnels

8.7.2 Travel Lanes The number of travel lanes is primarily based on a capacity analysis for the selected design year. The width of the travel lane will vary according to the functional class of the highway, traffic volumes, design speed, and level of development as presented in Table 8‐21A&B.

Table 8‐21A. Recommended Roadway Section Widths Freeways/Expressways

Travel Minimum Lane Width

Right Paved Usable Shoulder Width

(Min.)

Left Usable Shoulder w/4 or More Lanes Desirable Width

Left Usable Shoulder Width (Min.)

3.7 m 3.0 m 2.44 m (3.05 m*) 1.22 m

* With truck volumes over 250 vehicles/day

Note: 610 mm added to usable shoulder width for minimum offset to vertical elements over 200 mm high.


Table 8‐21B. Arterials Minimum Lane and Shoulder Widths

Roadway Classification

Travel Lane (m) Usable Shoulder (m)

Right Left

Desirable Min. Desirable ² Min. ³ Min.

Arterial 3.7 3.5 2.44 1.22 1.22 ¹

Collector 3.7 3.3 2.44 1.22 N/A

Local 3.7 3.0 1.22 0.61 N/A

Notes:

1. Only used when there is a median

2. Widths are to be determined based on traffic, pedestrian volumes, right‐of‐way restrictions, and environmental impacts.

3. Absolute minimum offset beyond usable shoulder to vertical element over 200 mm, or beyond travel lane if usable shoulder not provided is 0.50m.

4. Service roads or single‐lane local roads are to be 4.0m in lane width.

5. At signalized intersections, lane widths may be reduced. The absolute minimum is 3.0m.

6. For lane widening on curves, see Section 8.5.7 of this manual.

8.7.3 Shoulders The outer usable shoulders (normally 1.2 to 2.44m on arterial and low‐class roads, and 3.0m on expressways and freeways) serve several functions. They include:

3. An area for emergency stopping without disruption to traffic flow

13. An area for evasive action and recovery

14. Improvements to highway capacity, safety and driver comfort

15. Lateral support and drainage for the pavement to keep ponding away from travel lanes

16. Improvement of horizontal sight distances and increased lateral clearances to roadside appurtenances and other obstructions.

17. Providing additional lanes for diversions and space for road maintenance operations

The usable width of shoulder is the actual width that can be used when a driver makes an emergency stop. A side slope of 1v:6h or flatter can be used as a usable shoulder. The required width of usable shoulder is provided in Table 8‐21A&B.

Outer shoulders may not be required on urban undivided or divided roads (other than freeways and expressways), because structural support is provided by the curbs and channels, and disabled vehicles can generally find a safe place to stop in driveways and side streets. Nevertheless their adoption on collectors in industrial areas can be beneficial. At intersections, usable shoulders may be eliminated in order to better provide turning movements.

8.7.4 Curbing Curbs are used extensively on urban streets and highways. Generally, they are not used in rural areas, except with sidewalks where vertical barrier curb is required. Curbs serve to:


• Control drainage

• Restrict vehicles to the pavement area

• Define points of access to abutting properties

Vertical curbs should not be used on highways with design speeds of more than 70 km/h. If a curb is necessary in this case, a curb clearance of 0.6m should be added to the outside lane adjacent to curbed edges. Where there is a shoulder, there is no need to provide a curb clearance.

8.7.5 Borders, Buffer Strips and Sidewalks The border is the area acting as a buffer zone between the edge of pavement and the right‐of‐way line. Border areas separate the traffic from properties abutting the road or highway. On some roads, sidewalks are included within the border limits. In those cases, a minimum 600 mm buffer strip separating the sidewalk from the curb is desirable, provided sufficient right‐of‐way is available.

Borders are capable of accommodating road signs and structures, traffic control devices, traffic signals, utilities, lighting and landscaping features. The preferred location for these appurtenances (utility poles, fire hydrants, lighting, and traffic control boxes) is beyond the back of the sidewalk, especially when a travel lane is immediately adjacent to the curb.

Sidewalks are provided where they are justified by pedestrian activity. Sidewalk width varies according to projected use and available right‐of‐way, with 2.0 m preferred. In commercially developed areas, the entire area between the curb and buildings is often used as a paved sidewalk.

8.7.6 Medians Medians are used to separate opposing traffic lanes on multi‐lane roads. A median will provide many or all of the following benefits:

• Separation from opposing traffic reducing the likelihood of accidents and improving the traffic flow characteristics.

• Refuge for emergency stops

• Area for control of errant vehicles

• Reduction in headlight glare

• Area for deceleration and storage of mainline left‐turning and U‐turning vehicles

• Area for storage of vehicles crossing the mainline at intersection.

• Area for placement of luminaire supports, traffic signs, traffic signals, guardrail, landscaping, and bridge piers.

• Increased drainage collection area

• Refuge area for pedestrians and bicyclists.

• Area for future additional lanes

Medians may range in width from as little as 1.2m in an urban area to 20m or more in rural areas. Median width will depend on the following:

• Functional class


• Type of median

• Right‐of‐way available

• Traffic operations at crossing intersections

• Safety

It is recommended that urban medians be curbed. Rural medians should be provided with a 0.60 m or 1.22 m shoulder and not curbed; a depressed median is preferred to improve drainage. A curbed median, however, is desirable where there is a need to control left turn movements and when the median is to be landscaped. If the median is curbed and paved, the median surface should be designed to have slopes of 2 percent, and should fall away from the center of the median. Non‐paved medians should be depressed and slope towards the inside at 1V:6H for proper drainage, but consideration should be given to additional storage capacity or outlets for storm conditions. Paved medians may require incorporating drainage systems such as manholes, culverts, etc. All drainage inlets in the median should be designed with the top flush with the ground and safety gratings for culvert ends.

Table 8‐22 sets out the minimum widths for certain functional requirements of medians.

Table 8‐22. Minimum Median Widths for Certain Functions (m)

Requirements At Signalized Intersections

Elsewhere

Minimum to accommodate signal heads 1.2 to 1.6 ‐

Minimum curbed to separate traffic 1 1

Minimum to accommodate pedestrians 2.0 to 3.5 3.5

Minimum to provide left‐turn lanes 4.2 4.75

Minimum to provide U‐turn n/a 5.0

Minimum for landscaping provision n/a 8

Table 8‐23 provides the typical median widths based on roadway classifications.

Table 8‐23. Typical Median Widths (m)

Roadway Classification Urban Rural

Min. Desirable Min. Desirable

Freeways and Expressways 6.0 8.0 to 10.0 6.0 8.0 to 10.0

Primary Arterials 6.0 8.0 to 10.0 6.0 8.0 to 10.0*

Secondary Arterials 4.0 6.0 4.0 12.1*

Collectors 2.0 6.0 4.0 6.0

* Consideration for future lane widening


8.7.7 Cross Slopes Surface cross slopes are necessary on travel lanes to facilitate drainage. This reduces the hazard of wet pavements and standing water. On flexible pavements, travel lanes should be designed for a cross slope of 0.020 m/m. For outside shoulders, the cross slope is typically 0.030 m/m.

8.7.8 Side Slopes Cut and fill slopes should be designed to ensure the stability of the roadway and be as flat as possible to enhance the safety of the roadside. It is strongly recommended that an adequate geotechnical investigation be carried out prior to specifying the angles of side slopes. The engineer should consider the following when selecting a cut or fill design:

1. It is desirable for fill slopes on high speed roadways to be 1V:6H or flatter. All soils (except possibly wetland or much material) are stable at this rate. The angle of the side slopes must have regard to the nature of the material concerned. Rock cuttings in mountainous areas, for example, can be stable at relatively steep angles, whereas embankments built up from granular materials require shallow angles.

The slopes are generally traversable at 1V:6H. For fills greater than 5 m high in wetlands and in other sensitive areas, 1:2 slopes (with guardrail) are typical. Site conditions may require slopes up to 1:1. Slope retaining treatments such as geo‐textiles shall be considered for these situations.

2. Erosion possibilities must be minimized. Several rutted side slopes can cause vehicle rollover even on relatively flat slopes. In good soil, turf can be established on slopes as steep as 1:1. However, flatter slopes reduce the erosion potential and should be used where feasible. All slopes shall be planted with sufficient vegetation to stabilize the slope.

3. Where the highway mainline intersects a driveway, side road, or median crossing, the intersecting slopes need to be as flat as possible, preferably 1:12 or flatter; 1:6 slopes are acceptable.

4. For cut and fill sections, it may be necessary to reduce the required recovery widths for environmental, cost, right‐of‐way or aesthetic considerations. Guardrail should be used on fill slope where recovery area is not available. In cut sections, a ditch of sufficient width must be provided to maintain drainage flow from the hillside.

5. Side slopes can exist under the back spans of overhead bridges. It is typical for these side slopes to be paved. Aesthetics and bridge design normally dictate the slope. A maximum slope of 1:1½ is typically used.

8.7.9 Ditch Sections Roadside ditches divert and remove water from the surface and subsurface of the roadway. Roadside ditches can have several shapes: V, radial, trapezoidal, or parabolic. The trapezoidal ditch is the preferred shape when considering safety and ease of design, construction, and maintenance. Figure 8‐14 provides the design information for a typical trapezoidal roadside ditch. Roadway ditch foreslopes steeper than 1:6 are not desirable for safety reasons.


Figure 8‐14. Typical Ditch Section

Notes: 2. The bottom of the ditch should be below the bottom of the subbase. 3. Width can be wider to meet hydraulic requirements.

8.7.10 RightofWay Limits The right‐of‐way width should permit the design of a well‐balanced cross section, taking into account the road class, the projected traffic flows, topography, the surrounding land uses, and any other relevant parameters. The necessary right‐of‐way width is the summation of all cross section elements: lanes, shoulders, curbs, medians, sidewalks, buffer strips, clear zones, drainage ditches, utility accommodations, and frontage roads. Future roadway widening should also be taken into consideration.

Right‐of‐way width should be uniform. In urban areas, variable widths may be necessary due to the existing development; varying side slopes and embankment heights may make it desirable to vary ROW width; and ROW limits will likely have to be adjusted at intersections and freeway interchanges. Other special ROW controls are as follow:

• At horizontal curves and intersections, additional ROW acquisition may be warranted to ensure that the necessary sight distance is always available in the future.

• In areas where the necessary ROW widths cannot be obtained, the engineer will have to consider using steeper slopes, revising grades, or using slope retaining treatments.

• Right‐of‐way should be acquired and reserved for future improvements such as roadway widening and interchange completion.

• Temporary slope easements should be considered to minimize public ownership of land.

8.7.11 Horizontal Clearances It is important that structures and other roadside features be set back adequately from the edge of the traveled way. Where adequate clearances cannot be achieved, the structure or feature will require protection by means of a safety barrier.

The width of the necessary “clear zone” is dependent mainly on the design speed of the road, but also varies according to the side slope of the embankment, if any. Table 8‐24 shows the values of the clear zone width for different road conditions.


Table 8‐24. Clear Zone Width (m)

Design Speed (km/h)

Fill

At Grade

Cut

Side Slope 1:5*

Side Slope 1:6 or Flatter

Side Slope 1:6 or

Flatter

Side Slope 1:5 and 1:4

Side Slope Steeper Than 1:4

60 6 5 5 5 5 5

70 7 6 6 6 5 5

80 8 7 7 7 6 5

90 10 8 8 7 6 5

100 13 10 9 8 7 6

120 15 11 10 9 8 7

140 17 12 11 10 9 8

* Safety barrier is provided where side slope exceeds 1:5

These distances are measured from the nearest edge of the traveled way to the structure. Where this clear zone cannot be kept completely free from obstructions, safety barriers should be provided to protect the driver from a collision with a structure or an errant vehicle.

Safety barriers themselves need to be set back from the edge of the traveled way.

Table 8‐25 shows the relevant clearances.

Table 8‐25. Minimum Horizontal Clearances to Safety Barriers

Design Speed (km/h) Clearances of Safety Barriers from Edge of Traveled Way (m)

50 1

60 1.5

70 1.7

80 2

90 2.2

100 2.5

120 3

140 3.7

8.7.12 Others

8.7.12.1 Service Roads Service (Frontage) Roads run parallel, and are connected, to the main highway in both rural and urban areas. They control access to abutting properties, and in urban areas, they remove the roadside friction and parking from the main arterial. Service roads can be continuous or intermittent; can be on one or


both sides, and can be one‐way or two‐way. They segregate the higher speed through traffic from the lower speed local traffic.

Service roads may also provide an alternative route if maintenance is required on the mainline, or in case of an emergency.

The width of service road is dependent on the type and turning requirements of the traffic expected to use it. Service road connections to arterials should be designed as at‐grade intersections, while those for higher class roads should be designed as off‐ramps and on‐ramps.

The “Outer Separation” between the service road and the mainline should be 2.0m in minimum width. This width should include any signs or street lighting. A wider outer separation that includes landscaping to enhance the appearance of the road is preferred.

8.7.12.2 Auxiliary Lanes The purpose of the auxiliary lanes is one or more of the following:

• Speed change lane – used for either acceleration or deceleration.

• Climbing lane – introduced on steep up‐grades.

• Turning lane – permit those vehicles not proceeding ahead to undertake the necessary maneuver clear of the thru lanes.

• Additional storage space – required at some at‐grade intersections.

• A method of maintaining lane balance

• Weaving

More discussion on the auxiliary lanes is included in Section 8.8.5.

8.7.12.3 Bridges Bridges are designed for grade‐separated intersections, continuous viaducts and crossing rivers. The following general guidelines are important during bridge design phase:

• The engineer should establish the clearance requirements and the applicable design speeds, controlling grades and vertical curvature limits before beginning preliminary design.

• For preliminary design purposes, the depth of the bridge deck may be calculated as the sum of: approximately 1/8 of the longest span, 0.3m, cross‐slope difference, and deck surfacing. As the design progresses, this preliminary estimate should be replaced by the designed depth of structure, along with the proposed vertical geometry.

• Bridges with long spans, large skew angles, tapers or splays, small radius curvature, or large superelevation should be avoided, as they are likely to be costly and difficult to construct. They may also require a greater construction depth.

• The typical standards of the approaching roadway should be applied across the bridge, if possible.

• The bridge horizontal alignment should be straight. If horizontal curvature is inevitable, then the bridge should be on a circular curve rather than a transition, and the radius should be as large as possible.


• The skew angle should be less than 45 degrees.

• Avoid tapers and flared ends. If this is not possible, aim to start such changes in cross section at a pier position.

• For intermediate and wide medians, consider having two separate structures.

• Bridges should be set on straight grades (6% max. and 0.3% min. to permit longitudinal drainage) rather than on vertical curves. If this is not possible, crest curve should not be less than K=30.

• Avoid sag curves on bridges due to difficulties with drainage.

• Bridges should have Symmetrical spans. Abutments should be at the same elevation.

• Edge of curb profiles should be the same to avoid warped deck which is difficult to construct.

• The horizontal and vertical geometries of the bridge should be coordinated.

• Visibility requirements on a sag curve underneath a bridge should always be checked.

8.7.12.4 Tunnels Tunnels are expected to be designed and constructed in many locations in Libya. Shorter lengths of tunnel or underpass are often required and should be designed using the normal parameters. If it proves uneconomic to do so, each situation should be considered on its own merits. The following general guidance is given:

• The tunnel should be as short and straight as possible.

• The mainline typical section should desirably be continued through the tunnel, but in some circumstances it may not be an economical solution.

• Horizontal curvature in tunnels restricts sight distance. Widening on the inside of the curve is required to maintain proper SSD and design speed.

• Desirable vertical clearance should be maintained inside the tunnel. If this is not possible, special arrangements must be made for the diversion of oversized vehicles prior to reaching the tunnel.

• Sight envelopes given in Section 4 should be considered for the tunnel as vertical curvature can restrict visibility.

• Grades for tunnel should be selected based on values given in Section 6, lighting and ventilation requirements.

• The design should avoid the need for traffic signs to be provided within the tunnel.

• Merging, weaving, or diverging movements within a tunnel are undesirable. On‐ramps and off‐ramps should not be provided within tunnels, or for 300m outside the ends of the tunnel.

• Emergency and Fire alarm points are to be implemented in the tunnel.


• A raised sidewalk (minimum width is 0.7m) needs to be provided for emergencies and maintenance operations.

8.8 Grade Separations and Interchanges Interchanges and grade separations physically separate the through traffic movements of two intersecting highways. They eliminate dangerous crossings and may be used to bypass busy urban areas. Interchanges, unlike grade separations, provide access between the two highways by ramps.

8.8.1 Warrants The general warrants for interchange and grade separations include:

1. Design Designation – if a fully access‐controlled facility is provided, each intersecting highway must be terminated, rerouted, provided a grade separation, or provided an interchange. An interchange should be provided on the basis of the anticipated demand for access to the minor road. Interchange spacing is also a factor. In urban areas, a general rule is a 1.5 km minimum spacing between interchanges to allow the entrance and exit maneuvers. Closer spacing may require collector‐distributor roads to remove the merging and existing traffic from the mainline. In rural undeveloped areas, interchanges should be spaced no closer than 5.0 km apart.

2. Congestion – An interchange may be warranted where the level of service of an at‐grade intersection is unacceptable, and the intersection cannot be redesigned to operate at an acceptable level.

3. Safety – The accident reduction benefits of an interchange may warrant its selection at a particularly dangerous at‐grade intersection.

4. Site Topography – At some sites the topography may allow an interchange that would cost less than that of an at‐grade intersection.

5. Road‐User Benefits – Interchanges significantly reduce the travel time and costs when compared to at‐grade intersections. Therefore, if an analysis reveals that road‐user benefits over the service life of the interchange will exceed the costs, then the interchange will be warranted.

6. Traffic Volume – Interchanges are desirable at cross streets with heavy traffic volumes. The elimination of conflicts due to high crossing volume greatly improves the movement of traffic.

8.8.2 Interchange Types

8.8.2.1 Three‐Leg Three‐leg interchanges, also known as T or Y interchanges are provided where major highways begin or end. Figure 8‐15 illustrates examples of three‐leg interchanges with several methods of providing turning movements.


Figure 8‐15. Three‐Leg Interchanges

8.8.2.2 Diamond Diamond interchanges use one‐way diagonal ramps in each quadrant with two at‐grade intersections provided on the minor road. The diamond is usually the best choice of interchange where the intersection road is not access controlled. The advantages of diamond interchanges include:

1. All traffic can enter and exit the mainline at relatively high speeds. Adequate sight distance can usually be provided and operational maneuvers are normally simple.

2. Relatively little right‐of‐way is required

3. All exits from the mainline are made before reaching the structure

4. Left‐turning maneuvers require little extra travel distance


5. The diamond interchange allows modifications to provide greater ramp capacity, if needed in the future.

Figure 8‐16 illustrates a schematic of a typical diamond interchange.

Figure 8‐16. Typical Diamond Interchange (Schematic)

8.8.2.3 Cloverleafs Cloverleaf interchanges are used at four‐leg intersections with loop ramps to accommodate left‐turn movements. Full cloverleaf interchanges are those with loops in all four quadrants; all other are partial cloverleafs.

Where two access‐controlled highways intersect, a full cloverleaf is the minimum type design interchange that will suffice. However, these interchanges introduce several undesirable operational features such as:

• The double exits and entrances from the mainline

• The weaving between entering and exiting vehicles with the mainline traffic


• The lengthy travel time and distance for left‐turning vehicles

Figure 8‐17 provides typical examples of full cloverleafs with and without C‐D roads.

Figure 8‐17. Full Cloverleafs


Partial cloverleafs are appropriate where right‐of‐way restrictions preclude ramps in one or more quadrants. Figure 8‐18 illustrates six examples of partial cloverleafs. In these examples, the desirable feature is that no left‐turn movements are made onto the major road.

Figure 8‐18. Partial Cloverleaf Arrangements

8.8.2.4 Grade‐Separated Roundabouts A grade‐separated roundabout involves a conventional layout that would help in managing queues on off‐ramps. Figure 8‐19 illustrates two examples of a grade‐separated roundabout.


Figure 8‐19. Grade‐separated Roundabout

Arrangement (A) is the Simple form of intersection, using two bridges and a large rotary pavement. When traffic volumes increase, there is adequate space to permit the introduction of signals to the roundabout entries, and to further increase capacity by modest widening on the approaches.

At higher volumes still, arrangement (B) can be adopted. This layout, known as a three‐level roundabout, takes the cross‐traffic on a direct ramp, leaving the roundabout to handle only turning traffic. Such a layout can be introduced incrementally if the median of the cross route is constructed at the outset with a width sufficient to accommodate the future flyover. More discussion on roundabouts is included in Section 8.12.

8.8.3 Interchange Analysis Interchanges are expensive, and it is necessary to develop and study several alternatives in depth. Each alternative should be evaluated on the basis of its cost, safety, capacity, operation, and compatibility with the surrounding highway system.

8.8.3.1 Capacity and Level of Service An interchange must accommodate the anticipated traffic volumes. They are designed using the Design Hour Volumes (DHV) as described in Section 8.2. The capacity and level of service for an interchange will depend upon the operation of its individual elements along with the interaction and coordination of each of these elements in the overall design.

1. Basic freeway section where interchanges are not present.

2. Freeway‐ramp junctions or terminals

3. Weaving areas

4. Ramp proper

5. Ramp/Minor road intersection


It should be noted that the practical capacity of a single‐lane loop lies in the range 800 passenger cars per hour (pc/h) to 1200 pc/h. Loops rarely operate as two‐lane pavements, regardless of their width, and in general, they should not be designed to do so because of the difficulties in designing proper ramp terminals and for driver discomfort reasons. In general, therefore, then a DHV of around 1000 pc/h applies to the one‐way turning movement in one quadrant of an interchange, serious consideration should be given to the adoption of a form of connection other than a loop.

8.8.3.2 Selection of Interchange Type Freeway interchanges are of two general types. A “systems” interchange will connect freeway to freeway; a “service” interchange will connect a freeway to a lesser facility. Once several alternative interchange designs have been developed, they can be evaluated considering:

1. Compatibility with the surrounding highway system

2. Uniformity of exit and entrance patterns

3. Capacity and level of service

4. Operational characteristics (single versus double exits, weaving, signing)

5. Road user impacts (travel distance and time, safety, convenience and comfort)

6. Construction and maintenance costs

7. Right‐of‐way impacts and availability, and

8. Environmental Impacts

8.8.4 Traffic Lane Principles

8.8.4.1 Basic Number of Lanes and Freeway Lane Drops The basic number of lanes is the minimum number of lanes needed over a significant length of a highway based on the overall capacity needs of that section. The number of lanes should remain constant over short distances.

Freeway lane drops, where the basic number of lanes is decreased, must be fully designed. They should occur on the freeway mainline away from any other activity, such as interchange exits and entrances. The following recommendations are important when designing a freeway lane drop:

1. Location – The lane drop should occur approximately 600‐1000 m beyond the previous interchange. This distance allows adequate signing and adjustments from the interchange, but yet is not so far downstream that drivers become accustomed to the number of lanes and are surprised by the lane drop. In addition, a lane should not be dropped on a horizontal curve or where other signing is required, such as for an upcoming exit.

2. Sight Distance – The lane drop should be located so that the surface of the roadway within the transition remains visible for its entire distance. This favors placing a lane drop within a sag vertical curve rather than just beyond a crest. Decision sight distance to the roadway surface is desirable.


3. Transition – The desirable taper rate is 100:1 for the transition at the lane drop. The minimum is 70:1.

4. Right‐Side Versus Left‐Side Drop – All freeway lane drops must be on the right side, unless specific site conditions greatly favor a left‐side lane reduction.

5. Signing – Motorists must be warned and guided into the lane reduction. Advance signing and pavement markings should be implemented.

8.8.5 Lane Balance To realize efficient traffic operation through and beyond an interchange, there should be a balance in the number of traffic lanes on the freeway and ramps. Design traffic volumes and a capacity analysis determine the basic number of lanes to be used on the highway and the minimum number of lanes on the ramps. Variations in traffic demand should be accommodated by means of auxiliary lanes where needed.

After the basic number of lanes is determined for each roadway, the balance in the number of lanes should be checked on the basis of the following principles:

1. At entrances, the number of lanes beyond the merging of two traffic streams should not be less than the sum of all traffic lanes on the merging roadways, minus one.

2. At exits, the number of approach lanes on the highway must be equal to the number of lanes on the highway beyond the exit plus the number of lanes on the exit, less one. There is one exception – the short length of auxiliary lane that exists on a cloverleaf interchange between the on‐loop entrance and the off‐loop exit. In this case, the number of upstream lanes may be the same as the sum of the downstream lanes.

3. The traveled way of the highway should be reduced by not more than one traffic lane at a time.

Figure 8‐20 illustrates the typical treatment of the four‐lane freeway with a two‐lane exit followed by a two‐lane entrance.


Figure 8‐20. Coordination of Lane Balance and Basic Number of Lanes

8.8.5.1 Auxiliary Lanes As briefly discussed in Section 8.7.12, an auxiliary lane is defined as the portion of the roadway adjoining the traveled way for parking, speed change, turning, storage, weaving, truck climbing, and other supplementary to through‐traffic movement. An auxiliary lane may be provided to comply with the concept of lane balance, to comply with capacity requirements in the case of adverse grades, or to accommodate speed changes, weaving, and maneuvering of entering and leaving traffic. Where auxiliary lanes are provided along freeway main lanes, the adjacent shoulder would desirably be 2.0m to 3.7m in width.

Auxiliary lanes may be added to satisfy capacity and weaving requirements between interchanges and to accommodate traffic patterns variations at interchanges. The principles of lane balance must always be applied in the use of auxiliary lanes. Where interchanges are closely spaced in urban areas, the acceleration lane from an entrance ramp should be extended to the deceleration lane of a downstream exit ramp.

Figure 8‐21 shows alternatives in dropping auxiliary lanes.


Figure 8‐21. Alternatives in Dropping Auxiliary Lanes

8.8.6 Freeway/Ramp Junctions

8.8.6.1 Exit Ramps Exit ramps are one‐way roadways that allow traffic to exit from the freeway to provide access to other crossing highways. They are provided for all highways which intersect a freeway where the warrants for an interchange are satisfied.

Deceleration Lanes

Sufficient deceleration distance is needed to allow an exiting vehicle to leave the freeway mainline safely and comfortably. All deceleration should occur within the full width of the deceleration lane. The


length of the deceleration lane will depend upon the design speed of the mainline and the design speed of the first (or controlling) curve on the exit ramp. In addition, if compound curvature is used, there should be sufficient deceleration in advance of each successively sharper curve.

Deceleration lanes can be the taper type or the parallel lane type, with the parallel type preferred. It is necessary for a full deceleration lane to be developed and visibly marked well ahead of the gore area. Exit ramps diverge from the mainline at an angle between 2º and 5º. The parameters are shown in Figures 8‐22 thru 8‐25.

Figure 8‐22. Taper Type Exit Ramp (1‐Lane)


Figure 8‐23. Parallel Type Exit Ramp (1‐Lane)


Figure 8‐24. Taper Type Exit Ramp (2‐Lane with Lane Drop)


Figure 8‐25. Parallel Type Exit Ramp (2‐Lane without Lane Drop)

Figure 8‐26 provides the deceleration distance for various combinations of highway design speeds and exit curve design speeds. Deceleration lanes are measured from the point where the lane reaches


3.75 m wide to the painted nose for parallel types and the first controlling curve for taper types. Greater distances should be provided if practical. If the deceleration lane is on a grade of 3% or more, the length of the lane should be adjusted according to the criteria in Table 8‐26.

Figure 8‐26. Minimum Deceleration Lengths for Exit Terminals with Grades of 2% or Less

Superelevation

The superelevation at an exit ramp must be developed to transition the driver properly from the mainline to the curvature at the exit. The principles of superelevation for open highways, as discussed


in Section 5, should be applied to the exit design. The following criteria apply:

1. The maximum superelevation rate is 0.06 meter/mete

2. Preferably, full superelevation (0.06 m/m) is achieved at the PCC at the gore nose. However, this is subject to the minimum longitudinal slopes in Section 8.6.1.

3. The paved part of the gore is normally sloped at a 0.03 m/m rate.

8.8.6.2 Entrance Ramps

Entrance ramps are one‐way roadways that allow traffic from crossing highways to enter a freeway. They are provided for all highways that intersect a freeway where the warrants for an interchange are satisfied.

Acceleration Lanes

A properly‐designed acceleration lane will facilitate driver comfort, traffic operations, and safety. The length of the acceleration lane will primarily depend upon the design speed of the last (or controlling) curve on the entrance ramp and the design speed of the mainline. Typical layouts, showing geometric parameters, are given in Figures 8‐27 thru 8‐30. Where lane gain is indicated, the auxiliary lane may be merged with the nearside lane after a further distance of 400 m, using a taper rate of 1:50 for design speeds of 100 km/h and below, or 1:70 for higher speed roads.

Figure 8‐27. Taper Type Entrance Ramp (1‐Lane)


Figure 8‐28. Parallel Type Entrance Ramp (1‐Lane)


Figure 8‐29. Taper Type Entrance Ramp (2‐Lane with Lane Gain)


Figure 8‐30. Parallel Type Entrance Ramp (2‐Lane with Lane Gain)

Figure 8-31 provides the data for minimum lengths of acceleration lanes. These lengths are for the full width of the acceleration lane, and are measured from the end of the painted nose for parallel types, and from the end of the last controlling curve on taper types, to a point where the full 3.75 meter lane width is achieved. Taper lengths, typically 100 meters, are in addition to the table lengths. Where grades of 3% or more occur on the acceleration lane, adjustments should be made in its length according to Table 8-26.


Figure 8‐31. Minimum Acceleration Lengths for Entrance Terminals With Grades of 2% or Less


Table 8‐26. Speed Change Lane Adjustment Factors as a Function of Grade

Design Speed of Highway (km/h)

Deceleration Lanes

Ratio of Length on Grade to Length for Design Speed of Turning Curve (km/h)

All Speeds 3 to 4% Upgrade

0.9 3 to 4% Downgrade

1.2

All Speeds 5 to 6% Upgrade

0.8 5 to 6% Upgrade

1.35

Design Speed of Highway (km/h)

Acceleration Lanes

Ratio of Length on Grade to Length for Design Speed of Turning Curve (km/h)

40 50 60 70 80 All Speeds

3 to 4% Upgrade 3 to 4% Downgrade

60 1.3 1.4 1.4 ‐‐ ‐‐ 0.7

70 1.3 1.4 1.4 1.5 ‐‐ 0.65

80 1.4 1.5 1.5 1.5 1.6 0.65

90 1.4 1.5 1.5 1.5 1.6 0.6

100 1.5 1.6 1.7 1.7 1.8 0.6

110 1.5 1.6 1.7 1.7 1.8 0.6

120 1.5 1.6 1.7 1.7 1.8 0.6

5 to 6% Upgrade 5 to 6% Downgrade

60 1.5 1.5 ‐‐ ‐‐ ‐‐ 0.6

70 1.5 1.6 1.7 ‐‐ ‐‐ 0.6

80 1.5 1.7 1.9 1.8 ‐‐ 0.55

90 1.6 1.8 2.0 2.1 2.2 0.55

100 1.7 1.9 2.2 2.4 2.5 0.5

110 2.0 2.2 2.6 2.8 3.0 0.5

120 2.3 2.5 3.0 3.2 3.5 0.5


Superelevation

The ramp superelevation should be gradually transitioned to meet the normal cross slope of the mainline. The principles of superelevation for open highways, as discussed in Section 8.5, should be applied to the entrance design. The following criteria should be used:

1. The maximum superelevation rate is 0.06.

2. Preferably, the cross slope of the acceleration lane will equal the cross slope of the through land (0.02 m/m) at the PT of the flat horizontal curve near the entrance gore.

3. The superelevation transition should not exceed the minimum longitudinal slopes in Table 8‐14.

8.8.6.2 Weaving Areas Weaving occurs where one‐way traffic streams cross by merging and diverging maneuvers. This frequently occurs within an interchange or between two closely‐spaced interchanges. Figure 8‐32 illustrates a simple weave diagram and the length over which a weaving distance is measured.

Figure 8‐32. Weaving Sections

If the weave area is on a freeway, including weaving at cloverleaf interchanges, or if the site conditions will not allow the necessary distance, a collector‐distributor road should be provided.

8.8.6.3 Collector‐Distributor Roads Collector‐Distributor (C‐D) Roads are provided as a means of eliminating weaving on the mainline. They are normally found within an interchange, but may be considered for use between interchanges if


weaving difficulties are anticipated. C‐D roads are at least two lanes in width, and generally adopt a design speed 10 km/h to 20 km/h less than that of the mainline.

C‐D roads should be considered for all cloverleaf interchanges, which inherently generate significant weaving movements. When design weaving volumes exceed 1000 pc/h, C‐D roads should always be provided.

8.8.7 Capacity and Level of Service Factors that will affect the traffic operation conditions at freeway/ramp junctions are:

1. Acceleration and deceleration distances

2. Sight distance

3. Horizontal and vertical curvature at the junction

4. Merge and diverge volumes

5. Freeway volumes

Figure 8‐33 illustrates several ramp configurations with a table showing the volumes which can be accommodated at a ramp junction for a given level of service.


Figure 8‐33. Capacity of Ramp Configurations

8.8.7.1 Major Forks and Branch Connections Major forks are where a freeway or expressway separates into two freeways or expressways. Figure 8‐34 illustrates three schematics for a major fork. It is important that one interior lane has an option to go in either direction. This interior lane should be widened over a distance of about 300‐550 m.

Branch connections are where two freeways converge into one freeway. Figure 8‐35 illustrates two schematics for a branch connection. When a lane is dropped, as in “B,” this should be designed as a freeway lane drop (see Figure 8‐21)


Figure 8‐34. Major Forks

Figure 8‐35. Branch Connections


8.8.8 Ramp Design

8.8.8.1 Design Speed Ideally, the ramp design speed will approximate the low‐volume running speed on the intersecting highways. Where this is not practical, the values in Table 8‐27 should be used as the minimum design speed. These design speeds apply to the ramp proper and not to the freeway/ramp junction. If the two intersecting mainlines have different design speeds, the higher of the two should control at the entrance to the ramp. However, the ramp design speed should vary; the portion of the ramp nearer the lower‐speed highway is designed for the lower speed. There are 3 connection types:

• Free‐flow links ‐ connect the two alignments directly, turning through generally small angles.

• Ramps ‐ connect from a ramp terminal on one alignment to an at‐grade intersection on the other, and vice versa.

• Loops ‐ are also free‐flow between the two alignments, but typically turn through an angle of around 270 degrees.

Table 8‐27. Design Speeds for Connecting Roadways

Mainline Design Speed (km/h)

Design Speed for Connecting Roadway (km/h)

Free‐flow Links Ramps Loops

50 n/a 50 30

60 n/a 50 40

70 n/a 50 40

80 70 60 50

90 70 60 50

100 80 70 50*

120 100 80 50*

140 120 90 **

* Higher Design Speeds may be appropriate in rural areas.

** Loops on a 140 km/h design speed road should always be accessed via a C‐D road with a lower design speed.

8.8.8.2 Cross Section The following will apply to the ramp cross section:

1. Ramp Width – Ramps with a design speed of more than 60 km/h should have a right shoulder of 2.4 to 3.0 m and 3.0 to 1.8m left shoulder. For the other ramps, the sum of the right and left shoulder widths should not exceed 3.6 m, with a shoulder width of 0.6 to 1.2m on the left and the remainder as the right shoulder. The minimum width is 7 m for one lane ramps and 9 m for two lane ramps.

2. Cross Slope – Tangent sections of ramps should be uniformly sloped at 0.02 meter/meter from the median edge to the opposite edge. The maximum superelevation is 0.06 m/m.


3. Side Slopes – Fill and cut slopes should be as flat as possible. If feasible, they should be 1:6 or flatter thus eliminating the need for guardrail.

4. Bridges and Underpasses – The full width of the ramp or loop should be carried over a bridge or beneath an underpass.

5. Lateral Clearances to Obstructions – Best practice calls for the lateral clearance from the edge of the travel lane to be equal to its clear zone, as determined from the criteria in Section 7.

6. Exit Ramps – Where the through lane and exit ramp diverge, the typical width will be 7.75 m. This will be maintained until the gore nose is reached and transitioned to the standard 7 meter width at approximately a 12:1 rate.

7. Entrance Ramps – The standard 7 meter width will be transitioned to 5 m width at the convergence with the through lane.

8.8.8.3 Horizontal Alignment Horizontal alignment will largely be determined by the design speed and type of ramp. The following should be considered:

1. Table 8‐28 shows the minimum ramp radii required for the ramp design speed. Ramps should be designed for 50 km/h or greater unless restricted by site conditions.

Table 8‐28. Minimum Radii for Intersection Curves

Design (Turning) Speed V (km/h) 15 20 30 40 50 60

Side Friction Factor, f 0.40 0.35 0.28 0.23 0.19 0.17

Assumed Minimum e 0.00 0.00 0.02 0.04 0.06 0.08

Total e + f 0.40 0.35 0.30 0.27 0.25 0.25

Calculated Min. Radius (m) 5 9 24 47 79 113

Suggested Min. Radius Curve for Design (m)

7 10 25 50 80 115

Average Running Speed (km/h) 15 20 28 35 42 51

Note: For design speeds of more than 60 km/h, use values for open highway conditions.

2. Outer Connection – The outer connection at cloverleaf interchanges should be as directional as possible. However, if site conditions are restrictive, it may be allowed to follow a reverse path alignment around the inner loop.

3. Loops – Loop ramps should be on a continuously curved alignment in a spiral or compound curve arrangement.

4. Two‐Lane Ramps – The minimum radius is 100 m.


8.8.8.4 Vertical Alignment The minimum grade is 0.50%. General values of limiting gradient for upgrades are shown in Table 8‐29, but for any one ramp the selected gradient is dependent upon a number of factors. These factors include the following:

1. The flatter the gradient on the ramp, the longer it will be.

2. The steepest gradients should be designed for the center part of the ramp. Landing areas or storage platforms at at‐grade intersections with ramps should be as flat as possible.

3. Downgrades on ramps should follow the same guidelines as upgrades. They may, however, safely exceed these values by 2% with 8% considered the desired maximum grade.

4. K values and desirable stopping sight distance should be the minimum design for vertical curves.

Table 8‐29. Ramp Gradient Guidelines

Ramp Design Speed (km/h)

30 to 40 40 to 50 60 70 to 80

Maximum Desirable Grade Range (%) 6‐8 5‐7 4‐6 3‐5

8.8.8.5 Capacity Table 8‐30 provides the volumes for a given ramp design speed and level of service. 1500 pc/h should be used as a threshold to warrant a two‐lane ramp. The minimum radius of a two‐lane ramp should be 100 m. The capacity of a loop ramp is about 1250 pc/h; however, two‐lane ramps are undesirable because of their restrictive geometry. Therefore, if a left‐turn movement will exceed 1250, a directional or semi‐directional connection may be needed. Ramps must be designed with sufficient capacity to avoid backups on the mainline.

Table 8‐30. Service Volumes for Single‐Lane Ramps (Peak Hour Factor = 1.00; Values in Passenger Cars per Hour)

Level of Service Ramp Design Speed (km/h)

≤ 30 30‐50 50‐70 70‐80 ≥ 80

A ** ** ** ** 700

B ** ** ** 1000 1050

C ** ** 1125 1250 1300

D ** 1025 1200 1325 1500

E 1250 1450 1600* 1650* 1700*

F ‐ Widely Variable ‐

* For 2‐lane ramps, multiply above values by 1.7 for ≤ 30 km/h 1.8 For 30‐50, 70‐80 km/h 1.9 For 50‐70 km/h 2.0 For ≥ 80 km/h

** Level of service not achievable due to restricted design speed


8.8.9 Spacing of Ramp Terminals

8.8.9.1 Possible Arrangements There are four possibilities when considering two adjacent ramp terminals:

(1) Both are exits

(2) Both are entries

(3) The first is an exit, the second an entry

(4) The first is an entry, the second an exit

8.8.9.2 Exit/Exit Table 8‐31 shows minimum distances, measured from one painted nose to the next.

Table 8‐31. Minimum Spacing between Successive Exits

Minimum Distance From Preceding Exit Nose (m)

Freeways/ Expressways

Arterials/ Collectors/ C‐D Roads

Along the main lane 300 250

On a ramp or connecting roadway

In a free‐flow interchange

250

in other interchange

180

8.8.9.3 Entry/Entry When two traffic streams join, this generally produces an area of "turbulence" for a distance downstream. A subsequent entry therefore needs to be located far enough downstream to avoid this unstable area. Table 8‐32 shows the recommended spacing.

Table 8‐32. Minimum Spacing between Successive Entries




Along the main lane 300 250

On a ramp or connecting roadway

In a free‐flow interchange

250

in other interchange

180


8.8.9.4 Exit/Entry This is the safest of the four layouts, and this is reflected in the shorter distances shown in Table 8‐33.

Table 8‐33. Minimum Spacing between an Exit and an Entry


Freeway Expressway Arterials/Collectors/

C‐D Roads

150 120

8.8.9.5 Entry/Exit This is the most complex of the four layouts, as weaving of traffic streams generally occurs. Three considerations apply:

(1) There is a minimum distance between noses to ensure safe operation even under very light flow conditions ‐ this is the minimum spacing.

(2) There is a minimum distance between noses to permit the traffic streams in the design year to cross each other safety ‐ this is the weaving length.

(3) There is a spacing beyond which weaving is considered not to be a relevant factor ‐ this is the upper bound for weaving.

Considerations 1 and 3 are purely geometric and the relevant values are given in Table 8‐34. Consideration 2 is determined by the volumes of weaving traffic, and is dealt with in Section 8.8.6.

Table 8‐34. Spacing Criteria for Entry/Exit

Distance from Preceding Entry Nose (m)

Minimum Spacing Upper bound



For Clover Leaf Loops

All Types

Leading to, or leading from, free‐flow interchange

600 480 The minimum is dependent on the geometric design of the

clover‐leaf loops

3000

Between two other interchange

480 300 2000

8.8.10 Appendices Standard Designs for Freeway/Minor Road Interchanges (Cloverleaf and Diamond), Figure 8‐36 through Figure 8‐44.


Figure 8‐36. Freeway Exit at Interchange (Via Outer Connection of Cloverleaf Type Ramp)


Figure 8‐37. Freeway Exit at Interchange (From Inner Loop Cloverleaf Type Ramp)


Figure 8‐38. Freeway Exit at Diamond Interchange


Figure 8‐39. Freeway Entrance at Interchange (From Outer Connection Cloverleaf Type Ramp)


Figure 8‐40. Freeway Entrance at Interchange (From Inner Loop Cloverleaf Type Ramp)


Figure 8‐41. Freeway Entrance at Interchange (Diamond Type Ramps)


Figure 8‐42. Freeway Entrance – Exit at Interchange (Inner Loop Entrance – Inner Loop Exit of Cloverleaf Type Ramp)


Figure 8‐43. Exit at Interchange (Partial Cloverleaf Type Ramp)


Figure 8‐44. Diamond Ramps (Minor Roadway Exits and Entrances)


8.9 Summary of Design Parameters The following sections summarize the key geometric parameters relating to preferred design speeds for all roadway classifications.

8.9.1 Local Roads and Streets

Table 8‐34. Summary of Geometric Parameters for Local Roads and Streets

Geometric Parameter Rural

Local Road

Urban

Major Local Street

Minor Local Street

Traffic Calmed Layout

Preferred Design Speed (km/h) 60 50 40 30

Stopping Sight Distance (m) (level road) 85 65 50 35

Minimum Horizontal Radius (m) 150

(e=4%) 110

(e=2%) 70

(e=2%) 40*

(e=2%)

Maximum Superelevation (%) 4 2 2 2

Maximum Longitudinal Grade (%) 8 8 10 10

Minimum Longitudinal Grade (%) 0.2 0.2 0.2 0.2

Minimum Sag Curve K value 18 13 9 6

Minimum Crest Curve K value 11 7 4 2

Minimum Vertical Clearance (m) 5.5 5.5 5.5 5.5

* Lower radii are permissible for speed‐limiting bends


Figure 8‐45. Typical Section for Local Roads and Streets 1‐way, 1‐lane Local Street with Parallel Parking – Residential/Commercial (ROW 40')


Figure 8‐46. Typical Section for Local Roads and Streets 2‐way 2‐lane Local Street with Parallel Parking – Residential/Commercial (ROW 60')


Figure 8‐47. Typical Section for Local Roads and Streets 2‐way 2‐lane Local Street with Parallel/Angled Parking – Residential/Commercial (ROW 80')


8.9.2 Collectors

Table 8‐35. Summary of Geometric Parameters for Collectors

Geometric Parameter Rural Urban

Preferred Design Speed (km/h) 80 60

Stopping Sight Distance (m) (level road) 130 85

Safe Passing Sight Distance (m) (level road) 540 410*

Minimum Horizontal Radius (m) (for e=4%) 280 150

Maximum Superelevation (%) 6 4

Maximum Longitudinal Grade (%) 6 6

Minimum Longitudinal Grade (%) 0.2 0.2

Minimum Sag Curve K value 30 18

Minimum Crest Curve K value 26 11

Minimum Vertical Clearance (m) 5.5 5.5

* It is rarely necessary to provide safe passing sight distance on an urban collector.


Figure 8‐48. Typical Section for Collectors 2‐way 2‐lane Collector with Parallel Parking – Residential/Commercial (ROW 80')


Figure 8‐49. Typical Section for Collectors 2‐way 4‐lane Collector with Parallel Parking – Residential/Commercial (ROW 125')


Figure 8‐50. Typical Section for Collectors 2‐way 2‐lane Collector – Rural (ROW 80')


8.9.3 Arterials

Table 8‐36. Summary of Geometric Parameters for Arterials


Generally In CBD*

Preferred Design Speed (km/h) 100 100 80

Stopping Sight Distance (m) (level road) 185 185 130

Decision Sight Distance (m) (level road) 400 400 305

Minimum Horizontal Radius (m) (for e=4%) 490 490 280

Maximum Superelevation (%) 8 4 4

Maximum Longitudinal Grade (%) 6 6 6

Minimum Longitudinal Grade (%) 0.3 0.3 0.3

Minimum Sag Curve K value 45 45 30

Minimum Crest Curve K value 52 52 26

Minimum Vertical Clearance (m) 5.5 5.5 5.5

* CBD = Central Business District


Figure 8‐51. Typical Section for Arterials 2‐way 6‐lane Primary Arterial with Service Road and Angled Parking – Residential/Commercial (ROW 220')


Figure 8‐52. Typical Section for Arterials 2‐way 8‐lane Primary Arterial with Service Road and Angled Parking – Residential/Commercial (ROW 280')


Figure 8‐53. Typical Section for Arterials 2‐way 4‐lane Secondary Arterial with Service Road and Angled Parking – Residential/Commercial (ROW 180')


Figure 8‐54. Typical Section for Arterials 2‐way 4‐lane Secondary Arterial – Rural (ROW 125')


Figure 8‐55. Typical Section for Arterials 2‐way 4‐lane Secondary Arterial – Rural (ROW 180')


8.9.4 Freeways/Expressways

Table 8‐37. Summary of Geometric Parameters for Freeways/Expressways


Preferred Design Speed (km/h) 120 100

Stopping Sight Distance (m) (level road) 250 185

Safe Passing Sight Distance (m) (level road) 470 400

Minimum Horizontal Radius (m) (for e=4%) 670 400

Maximum Superelevation (%) 8 8

Maximum Longitudinal Grade (%) 4 4

Minimum Longitudinal Grade (%) 0.3 0.3

Minimum Sag Curve K value 63 45

Minimum Crest Curve K value 95 52

Minimum Vertical Clearance (m) 5.5 5.5


Figure 8‐56. Typical Section for Expressways 2‐way 6‐lane Expressway with Service Road and Angled Parking (ROW 300')


Figure 8‐57. Typical Section for Expressways 2‐way 8‐lane Expressway with Service Road and Angled Parking (ROW 300')


Figure 8‐58. Typical Section for Freeways 2‐way 8‐lane Freeway (ROW 300')


8.10 Highway Facilities

8.10.1 General This section discusses the following facilities and roadway features, and provides guidance on their design and provision:

• Pedestrian Facilities

• Public Transport Facilities

• Parking Facilities

• Safety Barriers

• Impact Attenuator Systems

• Traffic calming

• Pedestrian Facilities

8.10.1.1 Safety Most pedestrian accidents occur in urban areas and most of these occur at at‐grade intersections, but pedestrian safety is a concern in every highway design. The designer can then develop safety countermeasures. School locations and areas of high pedestrian volumes deserve particular attention. Following are examples of pedestrian safety measures:

5. Crosswalks should be provided at every intersection where pedestrians cross.

5. Sidewalks and other walkways which are designed to accommodate projected pedestrian volumes limit the use of streets and shoulders as walkways.

6. Signal phases which favor the pedestrian are desirable. These include pedestrian‐actuated signals and an exclusive pedestrian signal phase.

7. Where severe pedestrian safety problems exist or where there is a need to cross a free‐flow high‐speed highway, a pedestrian overpass would be required.

8. Other pedestrian safety measures include lighting, barriers and parking restrictions.

8.10.1.2 Sidewalks Sidewalks are provided where they are justified by pedestrian activity. Sidewalk width varies according to projected use and available right‐of‐way. In commercially‐developed and downtown areas, the entire area between the curb and buildings is often used as a paved sidewalk.

All urban roads should allow space for sidewalks, unless they are being specifically designed to prohibit walking. In areas with high volumes of pedestrian traffic, sidewalks should be provided on both sides of the road. Most service roads, however, require a sidewalk on one side only. Sidewalks should be continuous over the full pedestrian route.

It is desirable to have a sidewalk that is 3.0 m in width which would accommodate high pedestrian volumes or to accommodate both pedestrians and bicyclists in busy commercial areas. However, the recommended minimum sidewalk width is 1.8 m. It is also desirable to provide a 1.2m or more buffer strip between the curb and sidewalk for pedestrian safety from walking close to traffic.


8.10.1.3 Pedestrian Crossings Crossings are designated safety paths for pedestrians crossing at intersections or across a roadway for the continuity of pedestrian walkways/sidewalks. The choice of crossing facilities is as follow:

• Uncontrolled Marked Crossing. This type of crossing is marked with stripes on the pavement. It should only be provided on roads with a posted speed of 60 km/h or less, or on unsignalized right‐turning roadways within a signalized intersection where adequate Safe Crossing Sight Distance is available.

• Controlled Marked Crossing. Signals are used to bring traffic to a halt and to indicate to pedestrians that they may cross with care. This type of crossing exists most frequently within a signalized intersection, but can be provided on a free‐standing basis on roads with a posted speed of 80km/h or lower.

• Grade Separated Crossing. This is the form of crossing which is invariably required on freeways and expressways, and which may also be justified on arterials, depending on traffic volume and speed, and the number and nature of pedestrians crossing the road. It is provided by means of a pedestrian overpass or by a sidewalk on a grade‐separated road crossing.

The width of the pedestrian crossing should generally be 3.0m, but 2.44m should be the minimum width for a 2‐way crossing.

8.10.1.4 Pedestrian Overpasses Pedestrian overpasses should be considered where a combination of pedestrian volumes, traffic volumes, and pedestrian accidents indicates their use. The following are general guidelines:

6. Freeways may divide areas where pedestrian crossings would otherwise be high. If highway crossings are spaced relatively far apart, a pedestrian overpass may be justified.

9. Pedestrian overpasses may be warranted where a significant safety hazard exists.

10. The overpass must be able to accommodate handicap pedestrians by providing ramps with maximum grades of 8% and level landing areas of at least 1.5m in length.

8.10.2 Public Transport Facilities The location of bus stops is primarily the concern of the transportation authority in Libya, who will seek to provide stops within reasonable walking distance of trip generators and attractors. The bus stop spacing is normally 3 to 4 stops per kilometer in urban areas. The engineer should consult with the transportation authority to determine whether the road is to be used as a bus route, and, if so, to establish the desired general location of stops. Buses should be able to stop without obstructing the flow of traffic. Therefore, it is recommended to provide bus bays, which would allow the buses to stop without obstructing the flow of traffic. A preferred arrangement for a bus bay is shown in Figure 8‐59.


Figure 8‐59. Preferred Bus Bay Layout

On secondary arterials and collectors (and on local roads and streets if they are used by buses), it may be acceptable to permit buses to stop by the curb, provided that:

• The bus stop area is kept free from parked vehicles

• The bus stop is not located close to a major/minor intersection, and

• The presence of a stationary bus would not obstruct any relevant sight lines, and

• On an undivided road, the available forward visibility is at least half of the Safe Passing Sight Distance.

In addition, parking should be prohibited over a distance of 12m before and 8m beyond the bus stop area. Bus stops on undivided roads should be staggered, beyond each other, so that the view of crossing pedestrians from one bus is not obstructed by the presence of the bus traveling in the opposite direction. This arrangement also ensures that where two buses are dropping off passengers simultaneously, they do not have to set off through the crossing pedestrians dropped off by the other bus. When providing bus stopping points in the vicinity of intersections, the following points should be considered:

• In general, it is preferable to locate bus stops on the exit side of the intersection. A distance of at least 10m beyond the limit of the intersection would generally be required.

• If a bus stop is to be provided on the approach side, then it must be positioned sufficiently far in advance that the bus can move off safely and join the relevant traffic lane without undue


interference to other vehicles. A minimum distance of 20m from the end of the bay to the start of any right‐turning maneuver or auxiliary lane should generally be adequate, but the bay should be located such that a stationary bus is clear of the intersection sight triangles.

• Where a bus route turns right at an intersection, it may be possible to locate the stop on the approach side of the intersection, with the bus bay being located at the start of an extended right‐turning auxiliary lane.

• If a bus stop is located on the approach to a roundabout or signalized intersection, it should normally be located clear of any queuing vehicles, so that there is no loss of capacity at the intersection.

Figure 8‐60. Bus Stops at Intersections

8.10.3 Parking Facilities

8.10.3.1 General Where possible, parking should be provided remote from the road, in conveniently located parking lots designed for the purpose. On service roads and some collectors and local streets, it is however beneficial to include curbside parking where the adjoining land use warrants it.

Curbside parking should not be provided:

• within sight triangles at intersections, in order that visibility can be maintained, and pedestrians can cross unmasked;

• opposite access points to properties, unless there is adequate width for vehicles to enter and leave the property without impinging on the parking space;


• on bends, in order that adequate forward visibility can be maintained and that any encroachment into the path of oncoming vehicles is eliminated (note that parking on the outside of bends on local streets may be acceptable);

• at pedestrian crossing points, to minimize the width to be crossed by pedestrians;

• in advance of pedestrian crossing points, so that pedestrians can clearly see and be seen (note that an absolute minimum of 5 m free of parking should be provided, and ideally Safe Crossing Sight Distance, as set out in Section 8.11, should be provided at unsignalized crossings);

• at hydrants;

• on local roads, within 6m of the tangent point of any intersection;

• at any other location where it would create unsafe conditions

8.10.3.2 Curbside – Parallel Parking Parallel parking may be provided adjacent to the outer lane of the road. It is recommended that parallel parking should be provided only on roads of secondary arterial or lower class, or on service roads running adjacent to primary arterials and expressways.

The standard width required for a parallel parking lane is 2.5 m, each bay being nominally 6.5 m in length. If the majority of vehicles expected to use the facility are shorter than average, the bay length may be reduced to an absolute minimum length of 6.0 m. Where residential development is dense and the requirement for additional on‐street parking is great, it is possible in exceptional circumstances to use a narrower bay width, but the absolute minimum is 2.2 m.

8.10.3.3 Curbside – Angled Parking If the width of available right‐of‐way permits, consideration should be given to angled parking layout. These could be perpendicular to the road or at an angle in order to ensure that vehicles drive forwards into the bay and reverse out. Parking bay size for angled parking is 2.5 m wide by 5.0 m in length, but if desired and if space permits, the size may be increased to 2.7 m by 5.5 m (by increasing width and length dimensions by 10%) in order to provide a more generous layout which is easier to use. (Intermediate values of width and/or length may also be used.)

The amount of space which the bays occupy within the cross section of the road depends on their angle relative to the road, as shown in Table 8‐38 below.

Table 8‐38. Curbside Angled Parking ‐ Width Occupied within Cross Section of the Road (for a 5.0m x 2.5m bay)

Parking Angle Width occupied (m) allowing bumper overhang at curb

45° 4.70

60° 4.90

75° 4.75

90° 4.25


There is a need for adequate space to maneuver into an angled bay, and this usually requires the adjacent through lane to be wider than normal. If space permits, it is also good practice to provide a buffer lane between the edge of the traveled way and the nearest part of the parking bay. This is particularly beneficial on Service Roads, Collectors, and Secondary Arterials. Table 8‐39 shows these values.

Table 8‐39. Curbside Angled Parking Minimum Width for Adjacent Through Lane

Parking Angle Minimum width for through lane (m)

Buffer lane width (m)

Total Width (m)

45° 3.75 2.5 (desirable)

1.0 (minimum) OR NONE

3.75 – 6.25

60° 4.5 4.50 – 7.00

75° 6.5 6.50 – 9.00

90° 7.0 7.00 – 9.50

8.10.3.4 Parking Lots Parking lots are generally designed on the basis of angled parking, as this provides the most space‐efficient layout. The groups of bays are served by aisles, which generally operate one‐way. In the case of 90º angled bays, two‐way circulation is also possible without any increase in aisle width being required. Buffer lanes are not normally provided in parking lots.

When laying out a parking lot, it is generally found most efficient to align the aisles with the long axis of the plot, and to seek to maximize the number of bays located at the outer periphery of the available land, if it is regular in shape. Figure 8‐61 shows a parking lot laid out on these principles, and adopting a 90‐degree angle.


Figure 8‐61. Parking Lot Laid‐out with a 90‐Degree Angle

Figure 8‐62. Parking Bay Dimensions


Table 8‐40. Parking Lot Dimensions (m)

Dimensions (for a bay size of 2.5m x 5.0m)

DIM Angle

30° 45° 60° 75° 90°

Bay width A1 2.50 2.50 2.50 2.50 2.50

Bay width, parallel to aisle A2 5.60 3.50 2.80 2.70 2.50

Bay length B1 5.00 5.00 5.00 5.00 5.00

Length of line between bays B2 10.00 7.50 6.25 5.65 5.00

Bay depth to wall C1 4.50 5.30 5.60 5.50 5.00

Bay depth to curb C2 4.15 4.70 4.90 4.75 4.25

Bay depth to interlock C3 3.40 4.40 5.05 5.15 5.00

Aisle width between bay lines D 3.50 3.75 4.50 6.00 7.00

Bumper overhang (typical) E 0.35 0.60 0.70 0.75 0.75

Module, wall to interlock F1 11.40 13.45 15.65 17.75 18.00

Module, curb to interlock F2 11.05 12.85 14.95 17.00 17.25

Module, interlock to interlock F3 10.30 12.55 14.80 17.40 18.00

For trucks and other large vehicles

Bay dimensions are dictated by the size of the design vehicle, as set out in Table 8‐4, and the relevant templates need to be applied to determine the optimum layout. It is normal to provide a bay which is 1m wider than the width of the vehicle, with no addition to vehicle length, so a sports utility (SU) vehicle would require a bay of 3.6m by 9.1m. Shallow parking angles of 30 to 45 degrees are generally appropriate, with aisle widths being dependent on the design vehicle, but typically around 15 to 20m.

8.10.4 Safety Barriers

8.10.4.1 General A safety barrier is used to protect errant vehicles from impacting roadside objects and structures; and protects pedestrians and bicyclists from an out‐of‐control vehicle. Safety barrier can be located outside of the roadway or in the median, depending on the proximity of the hazard to the clear zone area. Single‐faced longitudinal barrier installed either in the median or on the outside of the roadway is a “Roadside Barrier.” Double‐faced longitudinal barrier which is designed to redirect vehicles striking either side of the barrier is “Median Barrier.”

Roadside barriers are usually categorized as flexible, semi‐rigid, or rigid, depending on their deflection characteristics on impact. Flexible systems are generally more forgiving than the other categories since much of the impact energy is dissipated by the deflection of the barrier and lower impact forces are imposed upon the vehicle. Rigid systems are generally more effective in performance and relatively low in cost when considering their maintenance‐free characteristics.


8.10.4.2 Warrants for Use of Safety Barriers The decision on whether or not to provide a safety barrier can often be simplified using the following analysis, with costs and likelihoods being considered where the decision is marginal.

• Option 1: Remove or reduce the hazard so that it no longer requires to be protected.

• Option 2: install an appropriate safety barrier.

• Option 3: Leave the hazard unprotected.

Medians

Head‐on impact with an opposing vehicle often leads to fatalities, and so a continuous safety barrier is often provided in the median of a divided road to separate opposing traffic. Such a barrier should always be provided on freeways and expressways, and should be considered on other roads carrying large traffic volumes at high speeds or where there is a fall across the median.

Embankments

The provision of safety barriers should be considered when slopes are steeper than 1 in 5 (20%) or the height of the slope is greater than 6m. The barrier should be set back from the usable shoulder, forward of the top of the slope, and not on the slope itself. Where barriers are not to be provided, rounding of the top of the slope reduces the chances of an errant vehicle becoming airborne.

Cut Areas

Safety barriers are seldom required in cut areas. Exceptions are where there is a steep rock face or where large boulders of other obstacles are located in the cutting slope.

Roadside Obstacles

A safety barrier should only be installed if it is clear that the result of a vehicle striking the barrier would be less severe than the accident resulting from hitting the unprotected object. Generally, if the clearance from the object to the edge of the traveled way is greater than 10m protection is not required. Refer to the clear zone criteria.

Protection of bystanders

Although roadside barriers are not particularly installed to protect bystanders or pedestrians but to protect vehicles from hitting roadside hazards, they provide protection and safety for pedestrians and bystanders from out‐of‐control vehicles.

Once it has been decided that a roadside barrier is warranted, the engineer must chose the appropriate type of barrier. This choice is based on a number of factors including performance criteria, cost (construction and maintenance), and aesthetics. Table 8‐41 summarizes the factors that should be considered.


Table 8‐41. Selection Criteria for Roadside Barriers

Criteria Comments

1. Performance Capability Barrier must be structurally able to contain and redirect design vehicle.

2. Deflection Deflection of barrier should not exceed available room to deflect

3. Site Conditions Slope approaching the barrier, and distance from traveled way, may preclude use of some barrier types.

4. Compatibility Barrier must be compatible with planned end anchor and capable of transition to other barrier systems (such as bridge railing)

5. Cost Standard barrier systems are relatively consistent in cost, but high‐performance railings can cost significantly more.

6. Maintenance

A. Routine Few systems require a significant amount of routine maintenance

B. Collision Generally, flexible or semi‐rigid systems requireSignificantly more maintenance after a collision than rigid Or high performance railings.

C. Materials Storage The fewer different systems used, the fewer inventory items/storage space required.

D. Simplicity Simpler designs, besides costing less, are more likely to be Reconstructed properly by field personnel

7. Aesthetics Occasionally, barrier aesthetics is an important consideration in its selection.

8. Field Experience The performance and maintenance requirements of existing systems should be monitored to identify problems that could be lessened of eliminated by using a different barrier type.

8.10.4.3 Flexible Barriers As was mentioned before, flexible barriers are generally more forgiving than the other categories since much of the impact energy is dissipated by the deflection of the barrier and lower impact forces are imposed upon the vehicle. There are two basic types of flexible system:

7. Cable Fence ‐ normally comprising 4 strands of tensioned cable. Cable fences redirect impacting vehicles after sufficient tension is developed in the cable, with the posts in the impact area providing only slight resistance. The closer the post spacing, however, the less the barrier can deflect. An important feature of the cable fence is that, after most impacts, it returns to its original position, and damaged posts are easily replaced.


11. Steel Beam ‐ the second type utilizes a standard steel beam section mounted on relatively weak posts. This system acts in a similar manner to the cable fence. It retains same degree of effectiveness after minor collisions due to the rigidity of the beam rail element. However, after major collisions it requires full repair to remain effective. As with the cable system, lateral deflection can be reduced to some extent by closer post spacing. This system, as with all barriers having a relatively narrow retraining width, is vulnerable to vaulting or vehicle under‐ride caused by incorrect mounting height or irregularities in the approach terrain.

8.10.4.4 Semi‐Rigid Barriers Semi‐rigid systems work on the principle that resistance is achieved through the combined flexure and stiffness of the rail. Posts near the point of impact are designed to break or tear away, distributing the impact force to adjacent posts. Lateral deflection of a semi‐rigid barrier may typically be as much as 1.5m.

Semi‐rigid barriers usually remain functional after moderate collisions, thereby eliminating the need for immediate repair. There are different types of systems with each having its own performance requirements and capabilities. A few examples are listed below.

• Box Beam

• Open Box Beam

• W‐Beam (corrugated type of barrier)

• Blocked Out W‐Beam

• Self‐restoring Safety Barrier

The self‐restoring safety barrier is a high performance barrier designed to be maintenance‐free for most impacts and capable of containing and redirecting large vehicles. The combination of high initial cost and high performance makes this barrier more suited for use at high accident frequency locations.

When traffic speeds are expected to be greater than 50 km/h the semi‐rigid system should be tensioned. Tensioned systems usually require a minimum length and radius to be effective (typically 50 m minimum length and 150 m minimum radius). Individual barrier manufacturers’ specifications should be adhered to.

8.10.4.5 Rigid Barriers Rigid systems offer no deflection when hit by a vehicle. The impact energy is entirely absorbed by the vehicle. For this reason, rigid barrier systems are not generally recommended for use on roads with design speeds over 100 km/h, and their proposed adoption on higher speed roads should be carefully evaluated by the designer. Commonly used rigid systems are the New Jersey shape and F‐shape Barriers in the USA, and the British Concrete Barrier in the UK. F‐shape barrier is preferred because of its better performance with small vehicle impact with respect to vertical roll and redirection.

Typically the system is relatively low cost, has generally effective performance for passenger‐sized vehicles, and has maintenance‐free characteristics. The details for this system are shown in the Construction Standards.


8.10.4.6 Placement Lateral offset from the road:

As a rule, safety barriers should be placed as far from the traveled way as conditions permit. This gives the errant driver the best chance of regaining control of the vehicle without having an accident. It also provides better sight distance. Table 8‐42 gives suggested lateral offsets related to the design speed, and it should be noted that these are from the edge of traveled way, not the pavement.

Table 8‐42. Suggested Setback from Edge of Traveled Way

Design Speed Setback from

Edge of Traveled Way (m)

50 1

60 1.5

70 1.7

80 2

90 2.2

100 2.5

120 3

140 3.7

Clearance between barrier and object being protected:

The desirable minimum distance between back of barrier and rigid hazards should not be less than the dynamic deflection of the safety barrier based on a vehicle impact condition of approximately 25 degrees and 100 km/h.

Manufacturers’ specific requirements must be followed. However, as a guide, the clearances set out in Table 8‐43 are typical.

On embankments care should be taken to ensure that at full deflection of the barrier the wheels of the vehicle do not overhang the edge of the slope.

The use of curbs with semi‐rigid or rigid safety barriers should generally be avoided, as impact with the curb causes instability in the vehicle’s progress prior to impact with the barrier. However, if the face of the safety barrier is laterally within 225 mm of the curb face a vehicle is not likely to vault the barrier, and the performance of the barrier should be within normal tolerances.

Table 8‐43. Clearance between Barrier and Object Being Protected

Barrier Type Clearance from Back of Barrier to Hazard (m)

Tensioned wire rope 2

Tensioned beam 1.2


Box beam 1.2

Rigid 0

Length of Need:

The barrier must be long enough to sufficiently shield the hazard from errant vehicles. Figure 8‐63 illustrates the typical guardrail layout for protection of a hazard. The minimum length of need for full height guardrail for 60 km/h, 100 km/h, and 110 km/h is 60 m, 90 m, and 100 m respectively. Barrier end treatment is in addition to the length of need. See Construction Standards for typical installation details of guardrail and concrete barrier.

On an undivided highway, the minimum guardrail length on the downstream end of the run to protect the opposing traffic from the hazard for 60 km/h, 80 km/h, 100 km/h and 110 km/h is 50 m, 60 m, 70 m and 70 m respectively.

Figure 8‐63. Barrier Length of Need

End Treatments:

The untreated end of any safety barrier is extremely hazardous if hit, as the beam element can penetrate the passenger compartment and will generally stop rather than redirect the vehicle. A crashworthy end treatment is therefore considered essential if the safety barrier terminates within 10m of the traveled way or in an area where it is likely to be hit end‐on by an errant vehicle.


The termination of the safety barrier should not spear, vault or roll a vehicle for end‐on or angled impacts. For impacts anywhere within the length of need, the performance of the barrier depends on that of the lengths adjacent to the point of impact. For potential impacts close to the end treatment zone it is therefore essential that the end treatment should have the same redirectional characteristics as the standard section. This means that the end must be properly anchored.

A number of different end treatments are available, working on a range of principles. Some of these are listed below.

• Breakaway Terminals

• Turned Down Terminals

• Energy Absorption Systems

• Special Anchorage for Cable Fence

• Anchorage into Embankment

Further reference is essential to select the most appropriate system for each particular situation.

Placement on Slopes and Behind Curbs:

If guardrail is improperly located on slopes or behind curbs, an errant vehicle could impact the barrier too high or too low, with undesirable results. Therefore, these criteria apply:

(a) Guardrail height is measured from the ground or pavement surface at the guardrail face. For W‐beam and Thrie beam this dimension is typically 550 mm from the surface to the center post bolt.

(b) Berm and curb must be located to minimize vaulting potential. See the Construction Standards for details.

(c) Where guardrail is required to be offset from the edge of pavement, it should not be placed on a slope steeper than 1V:12H.

Transitions:

Transition sections of safety barrier act as a link between lengths of different strength or rigidity, and are necessary:

• to provide continuity of protection when two different barriers join; or

• where a barrier joins another barrier system such as a bridge rail; or

• where a roadside barrier is attached to a rigid object such as a bridge pier

The transition section should be at least as strong as the stronger of the two sections which it links.

It should be long enough so that significant changes in deflection characteristics do not occur within a short distance. Generally the transition length should be 10 to 12 times the difference in the lateral deflection of the two systems in question, for example in a transition between a beam with a design deflection of 1.5m and a rigid barrier or abutment, the transition length should be around 15 to 18 m.


Drainage features such as ditches should be avoided at transition positions as they may initiate vehicle instability.

The stiffness of the transition should increase smoothly and continuously from the less rigid to the more rigid system. This can be achieved by decreasing the post spacing, increasing post size or strengthening the rail element.

8.10.5 Impact Attenuator Systems Energy absorbing barriers, also known as crash cushions or impact attenuator systems, are protective devices to prevent errant vehicles from impacting fixed object hazards. This is achieved by rapidly slowing down a vehicle, if possible, bringing it to a safe stop before the point of impact with the hazard. If stopping is not achievable, slowing it down would be to such an extent that the severity of the impact with the object is kept within sustainable limits. Some designs of impact attenuators also have the capability to deflect and redirect a shallow‐angle impact.

Impact attenuator systems are therefore designed specifically for use at locations where fixed objects cannot be removed, relocated or made to break away, and cannot be adequately protected by a normal safety barrier. They primarily serve to lessen the severity of an impact with a fixed object, unlike safety barriers which attempt to redirect the vehicle away from the object.

Impact attenuators work on one of two principles, namely absorption of kinetic energy or transfer of momentum.

In the first case, the kinetic energy of a moving vehicle is absorbed by hydraulic energy absorbers or crushable materials. This can be achieved by the use of water filled containers from which the water will be expelled in a collision, or by a progressively crushable mechanical array of elements. Crash cushions of this type require a rigid back stop to resist the impact force of the vehicle.

The second concept involves the transfer of momentum of a moving vehicle to an expendable mass of material or weights. This mass is often provided by a series of free‐standing sand filled containers. Devices of this type require no rigid back stop.

Energy absorbing barriers are generally appropriate for cars traveling at speeds of up to 100 km/h, but the system could be designed for trucks and buses too with various configurations.

The most common application of energy absorbing barriers is at an off‐ramp in a depressed or elevated structure, where a bridge pier or gore parapet requires protection and there is insufficient space for a conventional safety barrier lead‐in. Figure 8‐64 shows an energy absorbing barrier protecting an obstruction located in the gore area of an off‐ramp terminal.


Figure 8‐64. Impact Attenuator Protection to Obstruction Located in the Gore Area

For optimum performance, the barrier should ideally be on a relatively level surface. Curbs should not be provided as they may cause the vehicle to become airborne, thus coming into contact only partially with the crash cushion.

There are many different designs of impact attenuator systems, each of which has its own particular merits and applications. In the selection process, the road designer must consider the site characteristics, cost, maintenance requirements, and structural and safety characteristics of the different systems.

Further general reference on this subject is given in the American Association of State Highway and Transportation Officials’ publication, Roadside Design Guide. For details of any specific impact attenuator systems, the manufacturer’s technical literature should be referred to.

8.10.6 Traffic Calming

8.10.6.1 General Excessive vehicle speed is a significant factor in the majority of accidents in urban areas. Although the vehicles concerned may not have exceeded the posted speed, they have traveled faster than the prevailing conditions required. This is frequently due to the driver being "given the wrong signals" from the road infrastructure ‐ being unaware that he is driving at a speed much greater for the circumstances in which he finds himself (either associated with the road layout or related to other road users and those living in the area).

Traffic calming is a generic name for techniques of speed reduction through road design. The objective is to alter the driver’s perception of the road so that he drives at a speed which is appropriate. On roads of arterial standard and above, traffic calming is never appropriate because they require higher design


speeds. On urban collector roads, some elements of traffic calming may be appropriate, but the place where calming techniques are particularly relevant is in the design of local streets.

8.10.6.2 Objectives of Traffic Calming The main objectives are:

• to improve road safety

• to improve the quality of life for residents of the area

Secondary objectives are:

• to smooth the flow of traffic;

• to reduce the volume of traffic;

• to improve the environmental quality of roads;

• to discourage the use of unsuitable routes by heavy vehicles or streams of unnecessary through traffic;

• to limit vehicular atmospheric pollution; and

• to reduce traffic noise levels

The introduction of an area speed limit can assist in achieving these objectives, but unless the road is designed properly, the posted speeds are likely to be disregarded by many drivers.

There are four generic types of calming techniques: traffic engineering measures, visual features, horizontal alignment features and vertical alignment features.

8.10.6.3 Traffic Engineering Measures Intersection priority change

This can be introduced to break up a length of road which has priority through a series of intersections. Care needs to be taken in the signing of such a measure.

One‐way streets

The introduction of short lengths of one‐way operation can create a "maze"‐like road system, thus discouraging through traffic. The technique can also be used to limit traffic speeds by breaking up straight lengths of road into short sections, and can also permit the transfer of space from pavement to sidewalk or landscape use.

Shared surfaces

In appropriate circumstances it may be possible to provide an area to be used by both pedestrians and motorized traffic. It is essential in such areas to ensure that only very low vehicle speeds are achievable.

8.10.6.4 Visual Features Bar markings


These are colored road markings which can be laid across the road, particularly to draw attention to a change in speed limits. They may also be perceived by changes in tire noise.

Entry treatment

Where drivers enter a calmed road or area, it is usually helpful to draw this to their attention by use of different visual signals ‐ paving color, texture, or material being the usual method. Alignment features are often provided in association with entry treatments.

Gate ways

Gateways are a form of entry treatment, but with added vertical features such as walls or fences at right angles to the road, relatively close to the edge of the traveled way, to give a visual effect of narrowness.

Planting

The presence of tong sight lines can be a contributory factor to high speeds. Planting serves two purposes; first, to provide an enhanced environmental appearance, and second, to assist in keeping sight lines as short as possible, compatible with the very low design speeds which traffic calming adopts.

Rumble devices

These are textured areas of pavement which cause tire noise to be distinct, thus raising driver’s awareness.

8.10.6.5 Horizontal Alignment Features Speed Limiting Bends

These are tight curves, with inner curb radii in the range 10 m to 15 m. They should only be used where the other elements of the roadscape make it evident to drivers that traffic calmed behavior is expected. Drivers should be able to see the bend clearly on approach, but sight distances around the bend should deliberately be reduced by the provision of planting or hard landscaping. A stopping distance of 30m should be provided.

Build‐outs

These are local protrusions of the sidewalk into the pavement area, effectively narrowing the vehicular traveled way. They are often provided in combination with vertical features.

Chicanes

These consist of a pair of build‐outs on alternate sides of the road but not opposite each other, thus creating horizontal deflections which can only be negotiated by vehicles traveling at low speeds.

Medians

The introduction of a median (which may be raised or flush with the traveled way) on an undivided road has the effect of reducing lane widths and achieving effective visual narrowing. If space permits, the median can be planted, and apart from improving the amenity of the road this prevents excessive forward visibility. Figure 8‐65 shows this layout.


Figure 8‐65. Traffic Calming Layout Using Planted Median

Pinch points

These are locations where the road is deliberately made too narrow to permit two‐way operation, and vehicles have to operate in "shuttle" fashion, one direction at a time. On busier roads it may be necessary to give priority by signing to one direction of travel. Figure 8‐66 shows such an arrangement.

Figure 8‐66. Traffic Calming Layout Using Pinch Point

Sidewalk widening

Reallocation of space within the right of way can sometimes be achieved by widening sidewalks and reducing traffic space accordingly.

8.10.6.6 Vertical Alignment Features Sidewalk crosswalks

These allow pedestrians to continue at sidewalk level across an intersection, with the road being ramped up to sidewalk level and down again. In these installations, drivers are expected to give way to pedestrians.

Road humps

Humps are locally raised areas of pavement, typically 100 to 200 mm high and 4 m long (parallel to traffic direction), which can only be crossed comfortably by vehicles traveling at very low speeds.


Speed cushions

These are a form of flat‐topped road hump which extends across only part of the traveled way, allowing buses (with wider wheelbase) to pass on the level, but requiring cars to run one or both wheels over the cushion.

Speed tables

These are raised areas of pavement flush with the sidewalk, and are often provided over the whole area of an intersection.

Speed bumps

These are small road humps, typically up to 75 mm high. They are normally 0.3 m long (parallel to traffic direction) and laid in threes, at 1.3 m centers.

8.11 Intersections

8.11.1 General Design Considerations An intersection is the area where two or more roads join or cross at‐grade. It can be a major or minor intersection or a roundabout, which will be covered in Section 8.12. The intersection should be designed to accommodate an acceptable level of service. The values in Table 8‐2 should be met, when feasible, so that the highway facility will operate at a consistent level of service. At a minimum, the at‐grade intersection should operate at no more than one level below the values in the table.

Key issues to be addressed in the design of intersections include:

• Visibility

• Driver perception

• Signing and road marking

• Traffic control

• Design vehicle and geometric implications

• Pedestrian safety

8.11.1.1 Intersection Spacing The location of main intersections is generally dictated by the geographical position of the roads within the network, and intermediate intersections are usually a function of the surrounding area and its current or future development. The spacing of intermediate intersections is a balance between the needs of through traffic on the road and the requirement to access adjacent development.

Factors which should be taken into account when determining the need for an intersection (and hence the spacing of intersections) include:

• Roadway classification

• The general intersection spacing which applies to such a road class

• The potential traffic demand for access to/from the main road


• The length of the alternative route if no intersection is provided

• The design speed and posted speed of the road

• The lengths required for any weaving to occur safely

• Decision sight distances

• The physical dimensions of the intersection itself

Measures that can be used to reduce the number of intersections along a route include:

• Service roads for collecting local traffic movements together

• The closure of minor roads at the main road providing alternative access.

The information shown in Table 8‐44 should only be used as broad guidance when considering the minimum spacing of intersections.

Table 8‐44. Minimum Intersection Spacing (Measured center‐to‐center)

Roadway Classification Intersection Spacing (m)

Urban Areas Rural Areas

Freeway 1500 2000

Expressway 1000 2000

Primary Arterial 400 1500

Secondary Arterial 200 1000

Collector 100 100

Local Road No minimum specified 100

8.11.1.2 Capacity and Level of Service A capacity analysis must be performed during the design of any at‐grade intersection. A future design year, typically 20 years from the date the facility is completed, should be used. Often, the analysis will dictate several geometric design features such as approach width, channelization, exit width, and number of approach and exit lanes. As was mentioned before, the intersection should be designed to accommodate an acceptable level of service. Refer to Section 8.11.1.1.

8.11.1.3 Vehicle Considerations Vehicle turning paths yield minimum turning radii which are used in the design of intersections. Computer programs utilize turning movement analysis for the P, SU, BUS, A‐BUS, WB‐12, WB‐15, and WB‐18 vehicles. Normally, WB‐18 vehicle is not used for intersection design but generally restricted for freeways/expressways and their access roads. A vehicle must be able to negotiate the vertical profile at an intersection without dragging its underside or front and rear edges. This vehicle characteristic most often presents problems at driveway entrances and exits.

8.11.1.4 Alignment At‐grade intersections should occur on tangent sections of highway. Where a minor road intersects a major road on a horizontal curve, this complicates the geometric design of the intersection particularly sight distance, channelization, and superelevation. Preferably, the intersection should be relocated to a


tangent section of the major road. Another possibility is to realign the minor road to intersect the major road perpendicular to a tangent at a point on the horizontal curve. However, this arrangement would still result in difficult turning movements if the superelevation is high.

At‐grade intersections should be as close to 90 degrees as possible. Skewed intersections increase the travel distance across the major highway, adversely affect sight distance, and complicate the design for turning movements. Intersection angles of more than 30 degrees from the perpendicular cause particular problems. Skewed intersections should be realigned to 90 degrees, if possible, particularly for those which deviate by more than 30 degrees. Realignment shall be considered when accident data or traffic volumes indicate a need to do so.

8.11.1.5 Profile The vertical profile of an at‐grade intersection should be as level as possible, subject to drainage requirements. This also applies to the distance along any intersection leg, called the storage platform, where vehicles stop and wait to pass through the intersection. The storage platform typically should accommodate 3 vehicles with a gradient of 2%.

Grades approaching or leaving the intersection will affect vehicle deceleration distances (and therefore stopping sight distance) and vehicle acceleration distances. Where the grades exceed 3%, the stopping sight distance must be adjusted according to the criteria in Table 8‐8 in Section 8.4.

In general, the profile and cross section of the major road will be carried through the intersection, and the minor road will be adjusted to fit the major road. This will require transitioning the crown of the minor road to an inclined section sloped to fit the longitudinal gradient of the major highway. The transition should be gradual and comparable to the transition rates for superelevation as discussed in Section 5.6. Intersections of two major roadways should be graded to meet drainage and comfort considerations.

8.11.1.6 Vehicular Safety At‐grade intersections contribute significantly to the number of highway accidents. Many pedestrian accidents occur at urban intersections. In rural areas, there is normally a large speed differential between through vehicles and turning/entering vehicles. All at‐grade intersection safety problems can be minimized by proper design of its geometric elements: sight distance, roadway width, turning lanes, alignment and profile, channelization, and turning radii.

When redesigning an existing at‐grade intersection, the designer should review the accident history and/or analyze the accident patterns at that intersection. The designer should then include countermeasures to correct the problem. For example, several angle or rear‐end accidents involving left‐turning vehicles at an unsignalized intersection may indicate the need for an exclusive left‐turn lane.

The type and level of sophistication of traffic control will affect the safety and geometric design of the intersection. Following are examples of how geometric design and traffic control are related at an intersection:

1. At intersections with no signal control, the full pavement widths, including lane alignments, should be continued through.

2. Stop control may sufficiently reduce capacity to warrant additional approach lanes.


3. Stop and signalization control require the consideration of stopping or decision sight distance for the approaching vehicles.

4. Signalization will impact the length and width of storage areas, location, and position of turning roadways, and channelization. The number and type of lanes for signalized intersections will be significantly different than for unsignalized intersections.

5. The intersection must be designed to allow for physical placement of the traffic control devices in the safest location. Traffic control devices configuration must be coordinated with the local authority.

8.11.1.7 Control Signs and signals are employed to convey control information to the driver. Traffic signals have definite disadvantages and advantages and should be installed only after other less restrictive means of control, such as STOP and YIELD signs, have been employed without success.

Traffic control signals control vehicular and pedestrian traffic by assigning the right‐of‐way to various movements for certain pre‐timed or traffic‐actuated intervals of time. They are one of the key elements in the function of many intersections. Careful consideration should be given in plan development to intersection and access locations, horizontal and vertical curvature with respect to signal visibility, pedestrian requirements, and geometric schematics to ensure the best possible signal operation (individual signal phasing and traffic coordination between signals).

Traffic control signals should not be installed unless one or more of the signal warrants are met. Information should be obtained by means of engineering studies and compared with the requirements set forth in the warrants. If these requirements are not met, a traffic signal should neither be put into operation nor continued in operation (if already installed).

An investigation of the need for traffic signal control should include where applicable, at least an analysis of the factors contained in the following warrants:

Warrant 1 ‐ Minimum vehicular volume.

Warrant 2 ‐ Interruption of continuous traffic.

Warrant 3 ‐ Minimum pedestrian volume.

Warrant 4 ‐ School crossings

Warrant 5 ‐ Progressive movement.

Warrant 6 ‐ Accident experience.

Warrant 7 ‐ Systems

Warrant 8 ‐ Combination of warrants.

Warrant 9 ‐ Four Hour Volumes

Warrant 10 ‐ Peak Hour Delay


Warrant 11 ‐ Peak Hour Volume

When traffic control signals are not warranted but some control of the intersection is required, consideration may be given to the installation of STOP or YIELD signs.

A number of techniques are available for evaluating the operation of a signalized intersection, determining appropriate signal timing, and considering design alternatives. Among these techniques, the most important are:

(1) The “critical movement” based technique of the 2000 Highway Capacity Manual (HCM), latest edition.

(2) Computer software packages based on the HCM including: Highway Capacity Software (HCS), SIDRA (Signalized and Unsignalized Intersection Design and Research Aid), 94’ CINCH, and EzSignals.

(3) The signal‐optimization techniques incorporated in the latest versions of the following software packages: Synchro, 94’ CINCH and SIG/Cinema.

(4) Vehicle queue lengths using the following software packages: SIDRA, 94’ CINCH, and EzSignals.

The latest version of any of the above programs is acceptable for signal design and evaluation at isolated intersections.

For problems involving signal progression or coordination, the use of one of the following programs is encouraged:

(1) The latest versions of PASSER, Transyt, or Synchro are useful for designing or evaluating signal systems along an arterial or in a network.

(2) For simulation of signal operations on an arterial or in a network, the latest version CORSIM (Traf‐NETSIM) is recommended.

8.11.1.8 Other Considerations 1. Expectancy. Intersections are points of conflict between vehicles, pedestrians, bicycles, and

other users. Intersection design should permit users to discern and perform readily the maneuvers necessary to pass through the intersection safely and with a minimum of interference.

2. Pedestrians. Intersections are the most significant point where vehicles and pedestrians share roadways. When pedestrians approach an intersection, there is a major interruption. The sidewalk should provide sufficient storage area for those wanting to cross plus area for cross traffic to pass. The storage area (SA) necessary for pedestrians at a signalized intersection can be computed by the following formula:

SA = R(C – Gw) Ap

Where: R = rate of flow of pedestrians for design period, number/sec C = cycle length of signal, sec Gw = length of walk indication on the pedestrian signal, sec


Ap = storage area per person in queue (generally 0.5 square meter per person).

The designer should provide for the critical design period such as that containing the peak pedestrian flow, a period of heavy pedestrian cross‐traffic, or frequent interference from turning motor vehicles.

Once pedestrians are given the walk indication, the crosswalk width becomes important.

The crosswalk must be wide enough to accommodate the pedestrian flow in both directions within the duration of pedestrian signal phase. The necessary crosswalk width Xw can be estimated by the following equation:

Xw = (RC/P) (C/Gw)

Or the level of service at which an existing crosswalk is operating can be computed from:

P = (RC/Xw) (C/Gw)

When: R = Rate of flow of pedestrians for design period, number/sec C = cycle length of signal, seconds Gw = length of walk indication on the pedestrian signal, seconds Xw = crosswalk width, m; and P = pedestrian‐crossing volume in number/meter/minute.

From a pedestrian perspective, short crosswalks are desirable. If the intersection is not signalized or if stop signs do not prohibit conflict with vehicular traffic, pedestrians must wait for sufficient gaps in the traffic to cross. It is desirable for the pedestrian to cross the entire roadway in a single cycle and not be caught in the median. The clear area on the sidewalk free of obstructions should have a minimum 1.5 meter clearance between objects (poles, control boxes etc.).

3. The Handicapped. Design considerations for the handicapped should be included at intersections. The intersection plan should be evaluated for the convenient and safe locations of the ramps for the handicapped. Drainage inlets should be located on the upstream side of all crosswalks and sidewalk ramps. This design operation will govern the pedestrian crosswalk patterns, stop bar locations, regulatory signs, and in the case of new construction, establish the most desirable location of signal supports.

4. Bus Stops and Turnouts. The location of bus stops and turnouts can have a considerable impact on traffic flow, turning movements, sight distance, and pedestrian safety.

5. Bicycles. Intersections frequently present hazards for bicyclists. Pedestrian crosswalks at intersections can be utilized by bicyclists to cross over.

6. Access to Abutting Property. Intersection design elements, such as channelization, can eliminate access to abutting property. While such access control contributes to safety, it may upset the desired balance between access and mobility. Each intersection must be


evaluated independently to assure that design features are consistent with safety and the functional class of the roadways.

8.11.2 Intersection Sight Distance Two sight distance criteria must be met at intersections. First, the driver must be able to see the intersection itself. At a minimum, stopping sight distance must be provided to the intersection. However, decision sight distance is often the desirable treatment at inter‐sections because:

1. Many at‐grade intersections present roadway conditions that are too complex for the 2.5 second perception/reaction time factored into the stopping sight distances.

2. Decision sight distance allows time to conduct an evasive maneuver, which is desirable at intersections where slower moving, stopped, or crossing vehicles may be in the through lane.

3. Intersections often have high numbers of accidents. Therefore, the additional visibility proved by decision sight distance may be warranted.

When measuring for sight distance, the intersection surface should be used as a 0.0 meter height of object. Decision sight distance and its values are discussed in Section 8.4.3.

The second sight distance criterion which must be met is the corner sight distance along the legs of the intersecting highway. One of five sight distance conditions (or a combination) may apply at the intersection; these cases are discussed in the following sections. For each case, the criteria will determine what minimum sight triangle must be free of obstructions to allow the intended maneuver. In addition, for Case IIIA the applicable design vehicle must be selected based on the type and frequency of vehicles using the intersection.

No rigid criteria can be established for case selection. The designer must decide which of the five cases will be the design control based on an assessment of the functional classes of the intersecting highways, traffic control, traffic volumes, traffic composition, and highway design speed. Accident patterns may indicate where a critical problem exists and therefore which sight distance case should be selected.

8.11.2.1 Case I – No Control: Enabling Either Vehicle to Adjust Speed At intersections without traffic control, drivers should at a minimum be able to adjust their speed to avoid a collision. Figure 8‐67 provides the minimum sight distances along each intersecting leg assuming 3 seconds of perception/reaction time. Distances da and db can be extracted from the table for the sight triangle.


Figure 8‐67. Sight Distance at Intersections Minimum Sight Triangle No Control or Yield Control on Minor Road

The Case I distances are considerably less than the lower stopping sight distances. Therefore, the use of the Case I criteria should be limited to low‐volume, low‐speed intersections where attaining greater sight distance would be too costly. They typically apply to intersections in residential areas and between minor rural roads.

8.11.2.2 Case II – No Control: Enabling Either Vehicle to Stop At intersections without traffic controls, it is desirable to provide enough sight distance along the intersecting legs to allow either vehicle to stop. The Case II sight distances are provided in Figure 8‐67, which are the greater stopping sight distances. At restricted sites, the lower stopping sight distances may be used.


Where it is too costly to remove an obstruction which blocks the needed sight triangle, the Case II criteria can be used to determine the safe speed through the intersection. Advance warning signs should then be used to notify approaching drivers of the hazard

8.11.2.3 Case IIIA ‐ Stop Control: Enabling Vehicles to Cross a Major Highway At an intersection with stop control on the minor road, the driver of a stopped vehicle must have sufficient sight distance in both directions to cross a major road without interfering with oncoming vehicles. Figure 8‐68 provides an illustration of the Case IIIA layout and the necessary equations for computation of "d,” the sight distance needed in either direction. The following steps are necessary in the calculation:

1. Select the design vehicle. This should be the vehicle which will be making the crossing maneuver with considerable frequency to justify the sight distance provided.

2. Calculate the distance “S” the crossing vehicle must traverse. As shown in Figure 8‐68, this will depend upon the length of the vehicle, the width of the major highway, and the typical setback distance (usually 3 m).

3. Find ta the time needed to travel distance "S,” from Figure 8‐69. This will depend upon the selected design vehicle. The values from the figure are valid for relatively flat conditions.

4. Select a value "J,” the perception/reaction time for a driver to begin moving the vehicle. Normally, J is assumed to be 2.0 seconds. However, a somewhat lower value may be justified in urban areas where drivers use many intersections with stop control.

5. Calculate "d", the minimum sight distance along the major highway, from the equation in Figure 8‐68.

d = 0.28 V (J+ ta)

When testing for adequate sight distance, use a height of eye of 1070 mm and height of object of 1300 mm.


Figure 8‐68. Sight Distance at Intersections (Vehicle Crossing Major Highway from Stop – Case IIIA)


Figure 8‐69. Sight Distance at Intersections Case III, Acceleration from Stop)

Example (Case IIIA)

Given: Design speed of major highway ‐ 100 km/hr

W = 13 m

Problem: Determine required distance "d" for a passenger vehicle to cross the highway safely.

Solution: Step 1: Use a passenger vehicle.

Step 2: D = 3 m; W = 13 m; and L = 6 m; Therefore: S = 3 + 13 + 6 = 22 m


Step 3: From Figure 11.3 for "assumed P” ta = 5.7 sec,

Step 4: J = 2.0 sec.

Step 5: d = 0.28 x 100 (2.0 + 5.7) d = 216 m

8.11.2.4 Case IIIB (Left Turn) and IIIC (Right Turn) ‐ Stop Control If a vehicle operator intends to turn left or right onto a highway from a stopped position, additional sight distance is needed. Figure 8‐70 illustrates Case IIIB and Case IIIC. Figure 8‐71 provides the design criteria for the sight distance needed along the major highway. Preferably, the criteria for design speed should be used; the criteria for average running speed are acceptable as a minimum. Normally, sight distances for Case IIIB and IIIC should be satisfied. (Note: Criteria for buses and trucks have not been established. The corner sight distances for these vehicles would obviously be much greater.)

Cases IIIB and IIIC should be used at an intersection where the frequency of left‐turning and/or right‐turning vehicles justifies the additional costs of providing the sight distance. A review of the intersection accident history may indicate the extent of any sight distance problems.

Figure 8‐70. Intersection Sight Distance at At‐Grade Intersections


Figure 8‐71. Intersection Sight Distances at At‐Grade Intersection (Case IIIB and Case IIIC)

8.11.2.5 Case IV – Signal Control Due to a variety of operational characteristics associated with all intersections, sight distance based on the Case III procedures must be available to the driver. This principle is based on the increased driver workload at intersections and the problems involved when vehicles turn onto or cross the major highway. The problems associated with unanticipated vehicle conflicts at signalized intersections, such as, violation of the signal, right turns on red, malfunction of the signal, or use of flashing red/yellow mode, further substantiate the need for incorporation of Case III sight distance even at signal‐controlled intersections.


A basic requirement for all controlled intersections is that drivers must be able to see the control device soon enough to perform the action it indicates. At intersections where right turns on red are permitted, the departure sight line for right turning vehicles should be determined by the methods discussed in "Case IIIC, Turning Right into a Major Highway."

In addition, when determining sight lines for the design maneuver, the designer should consider the effects of roadside appurtenances, parked cars, or any other restriction to the sight line.

8.11.2.6 Effect of Skew Sight distance calculations must be adjusted when the angle of intersection is less than 60 degrees. Figure 8‐72 shows the adjusted sight triangles of oblique angle intersections. The following alterations are necessary in the analysis:

Because of the difficulty of looking for approaching traffic, the intersection should never be treated as Case I, even where traffic is light.

Treatments by Case II or Case III, whichever is larger, should be used at oblique angle intersections.

The d distance along the highway can be computed from the equation d = 0.28v (J‐ta) by reading ta from Table 8‐45.

Figure 8‐72. Sight Distance at Skewed Intersections


Table 8‐45. Acceleration Rates for Passenger Vehicles

Speed (km/h)

Distance (m)

ta (s)

30 25 5.7

40 40 7.3

50 70 9.8

60 110 12.3

70 160 15.2

80 235 18.8

90 325 22.4

100 455 27.4

110 650 33.9

8.11.2.7 Effect of Vertical Profile A vehicle descending a grade requires a somewhat greater distance to stop than does one on level grade: also, a vehicle ascending a grade requires less distance in which to stop. The effect of grade on acceleration can be expressed as a multiplicand to be applied to ta as determined for level conditions for a given distance. See Table 8‐46.

Table 8‐46. Effect of Gradient on Accelerating Time (ta) at Intersections

Ratio, Accelerating Time on Grade To Accelerating Time on Level Section

Crossroad Grade (%)

Design Vehicle ‐4 ‐2 0 +2 +4

P 0.7 0.9 1.0 1.1 1.3

SU 0.8 0.9 1.0 1.1 1.3

WB‐15 0.8 0.9 1.0 1.2 1.7

8.11.3 Intersection Turns

8.11.3.1 Design of Right Turns The following steps apply when designing an at‐grade intersection to accommodate right‐turning vehicles:

1. Select the design vehicle based on the largest vehicle likely to make the turn, unless this would be a relatively infrequent occurrence. (Typically use the Semi‐tractor combination or SU design vehicle where applicable).


2. Select the design speed at which the vehicle should be allowed to make the turn. The turning radii designs discussed in Section 8.11.3.1.1 are negotiable at speeds of 15 km/h or less. If higher turning speeds are desired, then a turning roadway should be used (Section 8.11.3.1.2).

3. Determine the tolerable encroachment onto other lanes. This will vary with traffic volumes, lane width, and one‐way or two‐way operation.

4. Determine the need for auxiliary turn lanes.

5. Determine the availability of right of way.

6. Consider the effects of parking on turning movements.

7. Evaluate the need to accommodate pedestrian movements.

8. Select the appropriate channelization treatment.

Turning Radii

Turning radii allow vehicles to negotiate a right turn. A curve radius with or without modification is used. The edge of pavement or curb line for a right turn can be designed by these methods.

1. Simple radius,

2. Simple radius with taper offsets,

3. 3‐centered symmetric compound curve,

4. 3‐centered asymmetric compound curve, or

5. Spiral curve

The simple radius with taper offset provides a good transition for the turning vehicle. Therefore, they should be used where practical. Table 8‐47 & Table 8‐48 provide the data for the two methods for various design vehicles and turning angles. These designs will allow the design vehicle to turn at speeds up to 15 km/h. Figure 8‐73 illustrates minimum designs for simple curves for passenger and single‐unit vehicles. Figures 8‐74 to 8‐77 provide the design details and examples for simple curve radii with taper offsets for 90 degrees, less than 90 degrees, and greater than 90 degrees angle of turns.

Table 8‐47. Minimum Edge of Traveled Way Designs for Turns at Intersection

Simple Curve Radius with Taper

Angle of Turn (degrees)

Design Vehicle

Simple Curve

Radius (m)Radius (m)

Offset (m)

Taper (m:m)

30 P 18 ‐ ‐ ‐

SU 30 ‐ ‐ ‐




Design Vehicle

Simple Curve

Radius (m) Radius (m)

Offset (m)

Taper (m:m)

WB‐12 45 ‐ ‐ ‐

Ws‐15 60 ‐ ‐ ‐

WB‐19 110 67 1.0 15:1

WB‐20 116 67 1.0 15:1

we‐29 77 37 1.0 15:1

WB‐35 145 77 1.1 20:1

45

P 15 ‐ ‐ ‐

SU 23 ‐ ‐ ‐

WB‐12 36 ‐ ‐ ‐

WB‐15 53 36 0.6 15:1

WB‐19 70 43 1.2 15:1

WB‐20 76 43 1.3 15:1

WB‐29 61 35 0.8 15:1

WB‐35 ‐ 61 1.3 20:1

60

P 12 ‐ ‐ ‐

SU 18 ‐ ‐ ‐

WB‐12 28 ‐ ‐ ‐

WB‐15 45 29 1.0 15:1

WB‐19 50 43 1.2 15:1

WB‐20 60 43 1.3 15:1

WB‐29 46 29 0.8 15:1

WB‐35 ‐ 54 1.3 20:1

75

P 11 8 0.6 10:1

SU 17 14 0.6 10:1

WB‐12 ‐ 18 0.6 15:1

WB‐15 ‐ 20 1.0 15:1

WB‐19 ‐ 43 1.2 20:1

WB‐20 ‐ 43 1.3 20:1

WB‐29 ‐ 26 1.0 15:1




Design Vehicle

Simple Curve


Offset (m)

Taper (m:m)

WB‐35 ‐ 42 1.7 20:1

90

P 9 6 0.8 10:1

SU 15 12 0.6 10:1

WB‐12 ‐ 14 1.2 10:1

WB‐15 ‐ 18 1.2 15:1

WB‐19 ‐ 36 1.2 30:1

WB‐20 ‐ 37 1.3 30:1

WB‐29 ‐ 25 0.8 15:1

WB‐35 ‐ 35 0.9 15:1

105

P ‐ 6 0.8 8:1

SU ‐ 11 1.0 10:1

WB‐12 ‐ 12 1.2 10:1

Ws‐15 ‐ 17 1.2 15:1

WB‐19 ‐ 35 1.0 30:1

WB‐20 ‐ 35 1.0 30:1

WB‐29 ‐ 22 1.0 15:1

WB‐35 ‐ 28 2.8 15:1

120

P ‐ 6 0.6 10:1

SU ‐ 9 1.0 10:1

WB‐12 ‐ 11 1.5 8:1

WB‐15 ‐ 14 1.2 15:1

WB‐19 ‐ 30 1.5 25:1

WB‐20 ‐ 31 1.6 25:1

WB‐29 ‐ 20 1.1 15:1

WB‐35 ‐ 26 2.8 15:1




Design Vehicle

Simple Curve


Offset (m)

Taper (m:m)

135

P ‐ 6 0.5 15:1

SU ‐ 9 1.2 8:1

WB‐12 ‐ 9 2.5 6:1

WB‐15 ‐ 12 2.0 10:1

WB‐19 ‐ 24 1.5 20:1

WB‐20 ‐ 25 1.6 20:1

WB‐29 ‐ 19 1.7 15:1

WB‐35 ‐ 25 2.6 15:1

150

P ‐ 6 0.6 10:1

SU ‐ 9 1.2 8:1

WB‐12 ‐ 9 2.0 8:1

WB‐15 ‐ 11 2.1 6:1

WB‐19 ‐ 18 3.0 10:1

WB‐20 ‐ 19 3.1 10:1

WB‐29 ‐ 19 2.2 10:1

WB‐35 ‐ 20 4.6 10:1

180

P ‐ 5 0.2 20:1

SU ‐ 9 0.5 10:1

WB‐12 ‐ 6 3.0 5:1

WB‐15 ‐ 8 3.0 5:1

WB‐19 ‐ 17 3.0 15:1

WB‐20 ‐ 16 4.2 10:1

WB‐29 ‐ 17 3.1 10:1

WB‐35 ‐ 17 6.1 10:1


Table 8‐48. Cross Street Width Occupied by Turning Vehicle for Various Angles of Intersection and Curb Radii


Figure 8‐73. Minimum Designs for Simple Curves


Figure 8‐74. Detailed Layout of Simple Curve Radius with Taper Offset (90 Degree Turn)


Figure 8‐75. Detailed Layout of Simple Curve Radius with Taper Offset (Angle of Turn ‹ 90 Degrees)


Figure 8‐76. Detailed Layout of Simple Curve Radius with Taper Offset (Angle of Turn › 90 Degrees)


Figure 8‐77a. Effect of Curb Radii on Turning Paths of Various Design Vehicles

Figure 8‐77b. Effect of Curb Radii on Turning Paths of Various Design Vehicles

Turning Roadways

Turning roadways are channelized areas which allow a right turn to be made away from the intersection area. They should be considered where:

1. it is desirable to allow right turns at 25 km/h or more

2. intersections are skewed; or


3. buses or semi‐trailers must be accommodated

Table 8‐49 provides the design data for the horizontal alignment, width, and superelevation for various design speeds. Figure 8‐78 illustrates a typical design for a turning roadway. These criteria apply to the design of a turning roadway.

1. Curvature ‐ 3 centered compound curves should be used. Table 8‐50 and Figure 8‐79 show the minimum design criteria.

2. Spirals ‐ May also be used for smoother transitions. See Table 8‐51 for minimum spiral lengths.

3. Superelevation ‐ Superelevation on turning roadways does not need to be developed to the strict criteria of open highways. A flexible approach may be used where superelevation is provided as site conditions allow. The maximum superelevation is 0.04 m/m. If possible, the superelevation should be developed in the same manner as described in Section 5 for deceleration lanes at freeway exits.

4. Speed‐Change Lanes ‐ For large differences between the design speeds of mainline and turning roadway, the designer should consider deceleration and acceleration lanes. The decision to use a speed‐change lane will depend upon the functional classification of the two highways, traffic volumes, accident history, design speed, and the speed differential between the mainline and turning roadway. Speed‐change lanes should be provided from high‐volume, high‐speed urban and rural arterials. Acceleration lanes are normally provided when the turning roadway is merging with these facilities. A 15:1 taper is sufficient for deceleration lanes, and a 25:1 taper is preferred for the acceleration lane.

Preferably, the length of the speed change lane should be determined from the criteria in Section 8.8 for interchanges.

Table 8‐49. Designs for Turning Roadways

Design1 Speed (km/h)

Side Friction

(f)

Assumed2 Superelevation

(e) e+ f

Minimum3 Radius (m)

Width4 (m)

A B C

30 .27 .02 .29 28 4.50 5.0 5.5

40 .23 .04 .27 46 4.25 5.0 5.25

50 .20 .04 .26 70 4.0 5.0 5.0

Notes: 1 For design speeds greater than 50 km/h use open highway conditions. 2 Superelevation is typically between .02 and .04 3 A flatter curve, no more than twice the minimum radius, should be used to transition into and out of the sharper radius. The minimum length of the flatter transition curve will be:

Radius (m) 30 45 60 75 90 120 150+

Minimum Length (m)

12 15 18 24 30 36 43

Desirable Length (m)

18 20 27 36 42 41 60


4 Add a minimum of 0.5 m and desirable 1.25 m on each side of a barrier curb. Traffic conditions are: A – Predominantly P vehicles, but some consideration for SU trucks; B – Predominantly SU vehicles, but some considerations for semitrailers; C – Sufficient bus and semitrailer vehicles to govern design (>10%)

Figure 8‐78. Typical Design for Turning Roadway


Table 8‐50. Minimum Designs for Turning Roadways

3‐Centered

Compound Curve


Design Classification

Radii (m)

Offset (m)

Width of Lane (m)

Approx. Island

Size (m2)

75

A 45‐23‐45 1.0 4.2 5.5

B 45‐23‐45 1.5 5.4 5.0

C 55‐28‐55 1.0 6.0 5.0

90*

A 45‐15‐45 1.0 4.2 5.0

B 45‐15‐45 1.5 5.4 7.5

C 55‐20‐55 2.0 6.0 11.5

105

A 36‐12‐36 0.6 4.5 6.5

B 30‐11‐30 1.5 6.6 5.0

C 55‐14‐55 2.4 9.0 5.5

120

A 30‐9‐30 0.8 4.8 11.0

B 30‐9‐30 1.5 7.2 8.5

C 55‐12‐55 2.5 10.2 20.0

135

A 30‐9‐30 0.8 4.8 43.0

B 30‐9‐30 1.5 7.8 35.0

C 48‐11‐48 2.7 10.5 60.0

150 A 30‐9‐30 0.8 4.8 130.0


B 30‐9‐30 2.0 9.0 110.0

C 45‐11‐48 2.1 11.4 160.0

NOTES: Asymmetric three‐centered compound curve and straight tapers with a simple curve can also be used without significantly altering the width of roadway or corner island size.

Painted island delineation is recommended for islands less than 7 m2 in size

Design Classification:

A ‐ Primarily passenger vehicles; permits occasional design single‐unit truck to turn with restricted clearances.

B ‐ Provides adequately for SU; permits occasional WB‐15 to turn with slight encroachment on adjacent traffic lanes.

C ‐ Provides fully for WB‐15.

Table 8‐51. Minimum Lengths of Spirals for Intersection Curves

Design (turning) speed (km/h) 30 40 50 60 70

Minimum radius 25 50 80 125 160

Assumed C 1.2 1.1 1.0 0.9 0.8

Calculated Length of Spiral (m) 19 25 33 41 57

Suggested Minimum Length Of Spiral 20 25 35 45 60

Corresponding Circular Curve Offset From Tangent (m)

0.7 0.7 0.7 0.8 0.9


Figure 8‐79. Designs for Turning Roadways with Minimum Corner Islands


8.11.3.2 Auxiliary Turning and Storage Lanes Warrants for Right‐Turn Lanes

Exclusive right‐turn lanes should be considered for at‐grade intersections, as follows:

1. at intersections with high‐speed and/or high‐volume turning movements;

2. at unsignalized intersections on two‐lane urban or rural highways which satisfy the criteria in Figure 8‐80.

3. at intersections where the accident experience, existing traffic operation, or engineering judgment indicate a significant hazard or capacity problem related to right turning vehicles


Figure 8‐80. Right‐Turn Warrants at Unsignalized Intersections on 2‐Lane Highways

Warrants for Left‐Turn Lanes

Exclusive left‐turn lanes should be considered for at‐grade intersections, as follows:

1. at intersections with major roads on urban and rural arterials;

2. at unsignalized intersections on two‐lane urban or rural highways which meet the criteria; Refer to Table 8‐51.

3. at intersections where the accident experience, existing traffic operations, or engineering judgment indicate a significant hazard or capacity problem related to left‐turning vehicles


Length of Auxiliary Turn and Storage Lanes

The length of the turning lane is the sum of its taper, deceleration, and storage lengths:

1. Taper ‐ A taper of 15: 1 should be used. Short curves should be used at the beginning and end of the taper.

2. Deceleration ‐ It is desirable for the lengths for deceleration to be the same as those given for deceleration lanes at freeway exits in Chapter 8 (Table 8‐1), and for all deceleration to occur within the full width of the turn lane. Figure 8‐81 provides the minimum criteria for the length of turn lanes.

3. Storage Length ‐ The storage length should be long enough to store the number of vehicles likely to accumulate in the design period. The following minimum criteria will apply:

(a) At unsignalized intersections the storage length should accommodate the number of turning vehicles likely to arrive in an average two‐minute period within the peak hour. As a minimum, 15 m should be allowed; if the turning traffic is over 10% trucks, a minimum of 25 m should be provided.

(b) At signalized intersections, the storage length should be based on 1.5 or 2.0 times the average number of vehicles that would store per cycle.

Table 8‐52. Guide for Left‐Turn Lanes on Two‐Lane Highways

Advancing Volume/Hour

Opposing Volume/Hour

Left Turns

5% 10% 20% 30%

60 km/h Operating Speed

800 330 240 180 160

600 410 305 225 200

400 510 380 275 245

200 640 470 350 305

100 720 515 390 340


800 800 280 210 135

600 600 350 260 170

400 400 430 320 210

200 200 550 400 270

100 100 615 445 295


800 230 170 125 115


600 290 210 160 140

400 365 270 200 175

200 450 330 250 215

100 505 370 275 240

Right and left‐turn lanes should be designed as follows:

1. Figure 8‐82 illustrates a typical right‐turn lane and a typical left‐turn lane (on a divided highway). Minimum distances for deceleration are provided.

2. Figure 8‐83 illustrates the typical treatment for developing a left‐turn lane on an undivided highway.

3. Figure 8‐84 illustrates the typical design for a by‐pass lane on low speed facilities in developed areas. This is a relatively inexpensive design to provide for through and left‐turn movements at unsignalized intersections. It is appropriate for T‐intersections where left‐turning volumes are light to moderate, where right of way is restricted, and accident history is negligible.

Figure 8‐82. Typical Right and Left Turn Lanes on Divided Highway

TYPICAL RIGHT TURN LANE

TYPICAL LEFT TURN LANE

NOTES:

1. Widths must be increased for curb offsets or shoulders, where applicable.


2. As shown in the figure, all deceleration will desirably occur after the full width of the turning lane begins. If possible, the criteria in Table 8‐53 should be used. However, in areas of restricted right‐of‐way, this may not be practical. Use the following minimum distances for deceleration:

Design Speed (km/h)

Length (m) (Deceleration and Taper – Grades 2% or Less)

50 70 m

60 100 m

80 130 m

Figure 8‐83. Typical Left‐Turn Lane on an Undivided Highway

NOTES:

1. Tables are based on:

A. Curve radii are minimum radii for open highway conditions for given design speed and a normal crown of 0.02 m/m, which is the typical cross slope.

B. Tangent Distance Assumes A Taper Of: L=Ws²/100

2. See Table 8‐82 For Details of Turning Lane Taper.

3. See Table 8‐82 for details of turning lane length.

4. Island may be raised, painted, or scored concrete.


Figure 8‐84. By‐Pass Lane in Highly Developed Areas on an Undivided Highway at Less than 60 km/h

NOTES:

1. L = Length, m

W = By‐Pass Lane Width, m

S = Design Speed, km/h

2. Increase Length If Storage Requirements Exceed 30 m.

3. May be used as an alternative to Figure 8‐83 in highly developed areas, where right‐of‐way is restricted.

Other Considerations

When designing an auxiliary turning and storage lane, these factors should also be considered:

4. Where the proper length of a turn lane cannot be provided or becomes prohibitive, the designer may consider a dual‐turn lane. Generally, a dual‐turn lane approximately 60% as long as a single‐turn lane will operate comparably. However, double left turns require a protected turn phase to operate properly.

12. A right‐turn lane in an urban area will often require parking restrictions beyond the usual restricted distances from the intersection. Also, it may require relocating near‐side bus stops to the far side of the intersection.

13. With sufficiently wide medians, a left‐turn lane may be offset 0.5 m or more from the inside through lane to provide a striped island between the two.

14. Medians must be designed to accommodate the turning radii of the design vehicle.

15. Pavement markings for lanes must line up from one side of the intersection to the other.

16. The width of the turn lane should be 3.0m minimum.

17. Median openings should be designed according to the criteria in Section 8.11.3.4.

8.11.3.3 Two‐Way Left‐Turn Lanes A continuous or two‐way left‐turn lane (2WLTL) is a paved, flush, traversable median which can be used for left‐turn storage in either direction. A 2WLTL may be considered in developed areas with frequent commercial roadside access and with no more than two through lanes in each direction.


Although the 2WLTL offers advantages, they are hazardous unless there is sufficient sight distance and adequate delineation. The following should be used as guidance in selecting and designing a 2WLTL:

5. A 2WLTL is limited to arterials with operating speeds of 70 km/hr or less.

18. The preferred lane width is 4.5 m with a minimum lane width of 3.75 m.

19. At minor intersections, the 2WLTL should be extended up to the intersection. At major and/or signalized intersections, the 2WLTL should be terminated in advance of the intersection. An exclusive left‐turn lane of the proper length should be provided.

20. Any 2WLTL must be clearly marked and adequately delineated to prevent possible use as a passing lane. Overhead signing should be used.

21. A 2WLTL may be used where average daily traffic through volumes are 10,000 to 20,000 (4 lane) and 5,000 to 12,000 (2 lane) and left turns consist of at least 70 mid‐block turns per 300 m during peak hour and/or 20% or more of the total volume. High left‐turning volumes combined with high average daily traffic (ADT) could possibly lead to operational and safety problems. Restricting all left turns except at public road intersections and indirect (jug handle) U‐turns, or providing a raised median, with left turn and/or U‐turn lanes should also be considered. Each site requires careful evaluation of the suitability of the 2WLTL.

8.11.3.4 Median Openings Median openings should be provided primarily at public road intersections and to allow left turns to and from the main highway.

In order to provide coordinated signal progression for mainline traffic, median openings should not be closely spaced. On major arterials, signalized intersections with median openings should be spaced no closer together than 500 m to 600 m. On minor arterials, signalized intersections with median openings should be spaced no closer together than 400 m to 500 m.

Median openings must be designed to accommodate left‐turning vehicles properly. Left‐turning vehicles trace essentially the same path as right‐turning vehicles. Figures 8‐85 and 8‐86 illustrate the design vehicle paths and provide the criteria for intersections with control radii 15 m and 23 m. The following criteria apply:

1. The nose should be designed to accommodate the traffic movement at the intersection.

2. The minimum lengths of median openings are 12 m and are shown on Table 8‐53 to Table 8‐56. Intersections on a skew may require larger openings.

3. The acceptable encroachment is the primary factor in selecting the design vehicle. The median opening figures illustrate how much the larger vehicles encroach on the adjacent lanes for a given design. The decision to use the SU or WB‐15 design is based on truck volumes, through traffic volumes, design speed, accident history, costs, signalization, and judgment.


Figure 8‐85. Minimum Design of Median Openings (SU Design Vehicle, Control Radius of 15 m)


Figure 8‐86. Minimum Design of Median Openings (WB‐12 Design Vehicle, Control Radius of 23 m)


Table 8‐53. Minimum Design of Median Openings (SU Design Vehicle, Control Radius of 15 m)

Width Median (m)

L=Minimum Length of Median Opening (m)

Semicircular Bullet Nose

1.2 28.8 28.8

1.8 28.2 22.8

24 27.6 20.4

3.0 27.0 1&6

3.6 26.4 17.4

4.2 25.8 15.9

4.8 212 15.0

&0 24.0 13.2

7.2 22.8 12.0 MIN

8.4 21.6 12.0 MIN

46 20.4 12.0 MIN

10.8 19.2 12.0 MIN

12.0 18.0 12.0 MIN

15.0 15.0 12.0 MIN

18.0 12.0 MIN 12.0 MIN

21.0 12.0 MIN 12.0 MIN

Table 8‐54. Minimum Design of Median Openings (WB‐12 Design Vehicle, Control Radius of 23 m)

Width Median (m)



1.2 43.8 35.6

1.8 43.2 34.5

2.4 42.6 33.0

3.0 42.0 31.5

3.6 41.4 30.0

4.2 40.8 28.8

4.8 40.2 27.6

6.0 39.0 2T5

7.2 37.8 23.4

8.4 36.6 21.9

9.6 35.4 20.1


Width Median (m)



10.8 34.2 18.6

12.0 30.0 17.1

18.0 27.0 12.0 MIN

24.0 21.0 12.0 MIN

30.0 15.0 12.0 MIN

33.0 12.0 MIN 12.0 MIN

36.0 12.0 MIN 12.0 MIN

Table 8‐55. Effect of Skew on Minimum Design for Median Openings (Typical Values Based on Control Radius of 15 m)

Skew Angle

(degree)

Width of Median (m)

Length of Median Opening Measured Normal to the Crossroad (m)

Semi‐ Circular

A

Bullet Nose

R For Design C

(m) Symmetrical

B Asymmetrical

B

0

3 27 19

6 24 13

9 21 12 MIN.

12 18 12 MIN.

15 15 12 MIN.

18 13 12 MIN.

10

3 32 24 23

6 28 17 16

9 25 14 12 MIN.

12 21 12 MIN. 12 MIN.

15 18 12 MIN. 12 MIN.


Skew Angle

(degree)

Width of Median (m)

Length of Median Opening Measured Normal to the Crossroad (m)

Semi‐ Circular

A

Bullet Nose

R For Design C

(m) Symmetrical

B Asymmetrical

B

18 14 12 MIN. 12 MIN.

20

3 36 29 27 29

6 32 22 20 28

9 28 18 14 26

12 24 14 12 MIN. 25

15 20 12 MIN. 12 MIN. 23

18 16 12 MIN. 12 MIN. 21

30

3 41 34 32 42

6 36 27 23 39

9 31 23 17 36

12 27 19 13 33

15 23 15 12 MIN. 30

18 18 12 12 MIN. 27

40

3 44 38 35 63

6 39 32 27 58

9 35 27 20 53

12 29 23 15 47

15 24 19 12 MIN. 42

18 19 15 12 MIN. 36


Table 8‐56. Design Controls for Minimum Median Openings

Control Radius (m)

Design Vehicles Accommodated 12 15 23

Predominant P SU WB‐12

Occasional SU WB‐12 WB‐15

8.12 Roundabouts

8.12.1 General Roundabouts are circular intersections with specific design and traffic control features. These features include yield control of all entering traffic, channelized approaches, and appropriate geometric curvature to ensure that travel speeds on the circulatory roadway are typically less than 50 km/h. Thus, roundabouts are a subset of a wide range of circular intersection forms.

A roundabout can be provided on any class of road where at‐grade intersections are permissible, and so is an appropriate form of intersection on all roads, except for freeways and expressways where at‐grade intersections are not to be used.

It is reasonable to assume that roundabouts on Local Roads will operate within capacity, and it is likely that roundabouts on Collectors can be designed to do so too. On Arterials, adequate capacity may often be difficult to achieve while maintaining a safe layout.

8.12.2 Design Principles The principal objective of roundabout design is to secure the safe interaction of traffic between crossing traffic streams with minimum delay. This is achieved by a combination of geometric layout features that should be matched to the volumes of traffic in the various streams, to vehicle speeds, and to any location constraints that apply. Roundabouts are defined by two basic operational and design principles:

• Yield‐at‐Entry: Also known as off‐side priority or the yield‐to‐left rule, yield‐at‐entry requires that vehicles on the circulatory roadway of the roundabout have the right‐of‐way and all entering vehicles on the approaches have to wait for a gap in the circulating flow. To maintain free flow and high capacity, yield signs are used as the entry control.

• Deflection of Entering Traffic: Entrance roadways that intersect the roundabout along a tangent to the circulatory roadway are not permitted. Instead, entering traffic is deflected to the right by the central island of the roundabout and by channelization at the entrance into an appropriate curved path along the circulating roadway.

From a safety viewpoint, the roundabout should be designed to limit through speeds by means of adequate deflection angles and entry path curvature, and this may constrain pavement widths and thus limit the available capacity. See Figure 8‐87.


Figure 8‐87. Deflection of Entering Traffic

8.12.3 General Features of a Roundabout

8.12.3.1 Layout A roundabout has a one‐way circulating pavement around a central island which is 4m or more in diameter. The entries are generally designed to permit more than one vehicle to enter the roundabout side‐by‐side, and the approaches may be "flared" to achieve adequate entry width. Figures 8‐88 and 8‐89 depict basic design and geometric elements of a roundabout. Entries from undivided roads should be provided with medians of divided roads should be widened in a similar manner. The minimum diameter for a central island is 4m. Flush paving should be considered for roundabouts with island diameters in the range 4m to 12m.


Figure 8‐88. Typical Roundabout Design

Figure 8‐89. Basic Geometric Elements of a Roundabout


8.12.3.2 Number of Entries The number of entries recommended is either three or four. Roundabouts perform particularly well with three legs, being more efficient than signals, provided that the traffic demand is evenly balanced between the legs. If the number of entries is greater than four, driver comprehension can be adversely affected. The roundabout also becomes target, and it is likely that higher circulating speeds will occur. Six legs should be considered as the absolute maximum.

8.12.4 Speeds through the Roundabout Because it has profound impacts on safety, achieving appropriate vehicular speeds through the roundabout is the most critical design objective. A well‐designed roundabout reduces the relative speeds between conflicting traffic streams by requiring vehicles to negotiate the roundabout along a curved path.

8.12.4.1 Speed profiles Figure 8‐90 shows the operating speeds of typical vehicles approaching and negotiating a roundabout. Approach speeds of 40, 55, and 70 km/h about 100 m from the center of the roundabout are shown. Deceleration begins before this time, with circulating drivers operating at approximately the same speed on the roundabout. The relatively uniform negotiation speed of all drivers on the roundabout means that drivers are able to more easily choose their desired paths in a safe and efficient manner.

8.12.4.2 Design speed International studies have shown that increasing the vehicle path curvature decreases the relative speed between entering and circulating vehicles and thus usually results in decreases in the entering‐circulating and exiting‐circulating vehicle crash rates. However, at multilane roundabouts, increasing vehicle path curvature creates greater side friction between adjacent traffic streams and can result in more vehicles cutting across lanes and higher potential for sideswipe crashes. Thus, for each roundabout, there exists an optimum design speed to minimize crashes.


Figure 8‐90. Sample Theoretical Speed Profile (Urban Compact Roundabout)

Recommended maximum entry design speeds for roundabouts at various intersection site categories are provided in Table 8‐57.

Table 8‐57. Recommended Maximum Entry Design Speeds

8.12.4.3 Vehicle Paths To determine the speed of a roundabout, the fastest path allowed by the geometry is drawn. This is the smoothest, flattest path possible for a single vehicle, in the absence of other traffic and ignoring all lane markings, traversing through the entry, around the central island, and out the exit. Usually the fastest possible path is the through movement, but in some cases it may be a right turn movement.

A vehicle is assumed to be 2m wide and to maintain a minimum clearance of 0.5m from a roadway centerline or concrete curb and flush with a painted edge line. Thus the centerline of the vehicle path is drawn with the following distances to the particular geometric features:


• • 1.5 m from a concrete curb,

• • 1.5 m from a roadway centerline, and

• • 1.0 m from a painted edge line

Figure 8‐91 and 8‐92 illustrate the construction of the fastest vehicle paths at a single‐lane roundabout and at a double‐lane roundabout, respectively. Figure 8‐93 provides an example of an approach at which the right‐turn path is more critical than the through movement.

Figure 8‐91. Fastest Vehicle Path through Single‐lane Roundabout


Figure 8‐92. Fastest Vehicle Path through Double‐lane Roundabout

Figure 8‐93. Example of Critical Right‐turn Movement

The design speed of the roundabout is determined from the smallest radius along the fastest allowable path. The smallest radius usually occurs on the circulatory roadway as the vehicle curves to the left around the central island. However, it is important when designing the roundabout geometry that the radius of the entry path (i.e., as the vehicle curves to the right through entry geometry) not be significantly larger than the circulatory path radius.


8.12.5 Design Vehicle An important factor determining a roundabout’s layout is the need to accommodate the largest motorized vehicle likely to use the intersection. The turning path requirements of this design vehicle will dictate many of the roundabout’s dimensions. Before beginning the design process, the designer must be conscious of the design vehicle and possess the appropriate vehicle turning templates or a CAD‐based vehicle turning path program to determine the vehicle’s swept path.

The choice of design vehicle will vary depending upon the approaching roadway types and the surrounding land use characteristics. Commonly, WB‐15 vehicles are the largest vehicles along collectors and arterials. Smaller design vehicles may often be chosen for local street intersections.

In general, larger roundabouts need to be used to accommodate large vehicles while maintaining low speeds for passenger vehicles. However, in some cases, land constraints may limit the ability to accommodate large semi‐trailer combinations while achieving adequate deflection for small vehicles. At such times, a truck apron may be used to provide additional traversable area around the central island for large semi‐trailers (Figure 8‐94). Truck aprons, though, provide a lower level of operation than standard non‐mountable islands and should be used only when there is no other means of providing adequate deflection while accommodating the design vehicle.

Figure 8‐94. Design Vehicle with the Use of an Apron

8.12.6 Inscribed Circle Diameter The inscribed circle diameter is the distance across the circle inscribed by the outer curb (or edge) of the circulatory roadway. As illustrated in Figure 8‐89, it is the sum of the central island diameter (which includes the apron, if present) and twice the circulatory roadway. The inscribed circle diameter (ICD) is determined by a number of design objectives. In general, the ICD should be a minimum of 30 m to accommodate a WB‐15 design vehicle. Smaller roundabouts can be used for some local street or collector street intersections, where the design vehicle may be a bus or single‐unit truck.

At double‐lane roundabouts, accommodating the design vehicle is usually not a constraint. The size of the roundabout is usually determined either by the need to achieve deflection or by the need to fit the


entries and exits around the circumference with reasonable entry and exit radii between them. Generally, the inscribed circle diameter of a double‐lane roundabout should be a minimum of 45 m.

The size of the smallest acceptable ICD is determined by the selected design vehicle. It is good practice to allow a tolerance of 1.5m from both inner and outer curbs, and so typical minimum lCDs are as set out in Table 8‐58.

Table 8‐58. Recommended Inscribed Circle Diameters

Site Category Typical

Design Vehicle Inscribed Circle Diameter Range*

Mini‐Roundabout Single‐Unit Truck 13 – 25m

Urban Compact Single‐Unit Truck/Bus 25 – 30m

Urban Single Lane WB‐15 30 – 40m

Urban Double Lane WB‐15 45 – 55m

Rural Single Lane WB‐20 35 – 40m

Rural Double Lane WB‐20 55 – 60m

* Assumes 90‐degree angles between entries and no more than 4 legs.

In general, smaller inscribed diameters are better for overall safety because they help to maintain lower speeds. It should be noted, however, that if roundabouts are below 40m ICD it can prove difficult to achieve adequate deflections. In such cases consideration could be given to the use of a larger, low‐profile central island which would provide adequate deflection for standard vehicles but allow overrun of all or part of the island by the rear wheels of articulated vehicles and trailers.

In high‐speed environments, however, the design of the approach geometry is more critical than in low‐speed environments. Larger inscribed diameters generally allow for the provision of better approach geometry, which leads to a decrease in vehicle approach speeds. Larger inscribed diameters also reduce the angle formed between entering and circulating vehicle paths, thereby reducing the relative speed between these vehicles and leading to reduced entering‐circulating crash rates.

8.12.7 Circulating Roadway Width The circulating roadway pavement width should, if possible, be circular in plan, and its width should generally not exceed 15m. However, flush block‐paved 'collars' around the central island can be used to provide additional width if long vehicle turning movements need to be catered for on smaller roundabouts.

The width of the circulating pavement should be constant and should be between 1.0 and 1.2 times the width of the widest entry. It may be necessary to exceed 1.2 on smaller ICD roundabouts, but care


should be taken to ensure that the wider pavement does not permit vehicle paths with less than adequate deflection.

It is normal practice to avoid short lengths of reverse curve between an entry and the subsequent exit by joining those curves with tangents between the entry and exit curves. One method is to increase the exit radius. However, where there is a considerable distance between the entry and the next exit, as with three‐leg layouts, reverse curvature may be unavoidable. The circulating pavement must be wide enough to allow those vehicles which have entered the roundabout side‐by‐side to continue side‐by‐side. Allowance should be made for increased width because of the curve, as set out in Table 8‐59. For island diameters less than 30m, the width requirements should always be checked using a relevant software package or swept path templates.

Table 8‐59. Minimum Width of Circulating Pavement

Island Diameter (m)

Circulation

2‐Lane 3‐Lane

30 12.6 Check using

Template50 11.1

75 10.3 15.0

100 9.9 14.7

150 9.3 13.8

200 9.0 13.2

250 8.7 12.6

8.12.8 Entry Width Entry width is the largest determinant of a roundabout’s capacity. The capacity of an approach is not dependent merely on the number of entering lanes, but on the total width of the entry. In other words, the entry capacity increases steadily with incremental increases to the entry width. Therefore, the basic sizes of entries and circulatory roadways are generally described in terms of width, not number of lanes. Entries that are of sufficient width to accommodate multiple traffic streams (at least 6.0m) are striped to designate separate lanes. However, the circulatory roadway is usually not striped, even when more than one lane of traffic is expected to circulate. The practical range for entry width is 6.0m to 15.0m, but for undivided roads, the upper limit should be 10.5m.

As shown in Figure 8‐97, entry width is measured from the point where the yield line intersects the left edge of the traveled‐way to the right edge of the traveled way, along a line perpendicular to the right curb line. The width of each entry is dictated by the needs of the entering traffic stream. It is based on design traffic volumes and can be determined in terms of the number of entry lanes. The circulatory roadway must be at least as wide as the widest entry and must maintain a constant width throughout.

To maximize the roundabout’s safety, entry widths should be kept to a minimum. The design should provide the minimum width necessary for capacity and accommodation of the design vehicle in order to


maintain the highest level of safety. Typical entry widths for single‐lane entrances range from 4.3 to 4.9m; however, a minimum entry width should not be less than 4m for the accommodation of trucks and buses.

When the capacity requirements can only be met by increasing the entry width, this can be done in two ways:

By adding a full lane upstream of the roundabout and maintaining parallel lanes through the entry geometry; or

By widening the approach gradually (flaring) through the entry geometry.

Figures 8‐95 and 8‐96 illustrate these two widening options.

Figure 8‐95. Approach Widening by Adding Full Lane


Figure 8‐96. Approach Widening by Entry Flaring

Flaring is an effective means of increasing capacity without requiring as much right‐of‐way as a full lane addition. While increasing the length of flare increases capacity, it does not increase crash frequency. Entry widths should therefore be minimized and flare lengths maximized to achieve the desired capacity with minimal effect on crashes. Generally, flare lengths should be a minimum of 25m in urban areas and 40m in rural areas. However, if right‐of‐way is constrained, shorter lengths can be used with noticeable effects on capacity.

8.12.9 Entry Curves The entry radius is an important factor in determining the operation of a roundabout as it has significant impacts on both capacity and safety. The entry radius, in conjunction with the entry width, the circulatory roadway width, and the central island geometry, controls the amount of deflection imposed on a vehicle’s entry path. Larger entry radii produce faster entry speeds and generally result in higher crash rates between entering and circulating vehicles. In contrast, the operational performance of roundabouts benefits from larger entry radii.

The entry curve is designed curvilinearly tangential to the outside edge of the circulatory roadway. Likewise, the projection of the inside (left) edge of the entry roadway should be curvilinearly tangential to the central island. Figure 8‐97 shows typical roundabout entrance geometry.


Figure 8‐97. Typical Roundabout Entrance Geometry

8.12.9.1 Entry Curves at Single‐lane Roundabouts For single‐lane roundabouts, it is relatively simple to achieve the entry speed objectives. With a single traffic stream entering and circulating, there is no conflict between traffic in adjacent lanes. Thus, the entry radius can be reduced or increased as necessary to produce the desired entry path radius. Provided sufficient clearance is given for the design vehicle, approaching vehicles will adjust their path accordingly and negotiate through the entry geometry into the circulatory roadway.

Entry radii at urban single‐lane roundabouts typically range from 10 to 30m. Larger radii may be used, but it is important that the radii not be so large as to result in excessive entry speeds. At local street roundabouts, entry radii may be below 10m if the design vehicle is small.

At rural and suburban locations, consideration should be given to the speed differential between the approaches and entries. If the difference is greater than 20 km/h, it is desirable to introduce approach curves or some other speed reduction measures to reduce the speed of approaching traffic prior to the entry curvature.

8.12.9.2 Entry Curves at Double‐lane Roundabouts At double‐lane roundabouts, the design of the entry curvature is more complicated. Overly small entry radii can result in conflicts between adjacent traffic streams. This conflict usually results in poor lane utilization of one or more lanes and significantly reduces the capacity of the approach. It can also degrade the safety performance as sideswipe crashes may increase.

8.12.10 Exit Curves Exit curves usually have larger radii than entry curves to minimize the likelihood of congestion at the exits. This, however, is balanced by the need to maintain low speeds at the pedestrian crossing on exit. The exit curve should produce an exit path radius (R3 in Figure 8‐98) no smaller than the circulating path radius (R2). If the exit path radius is smaller than the circulating path radius, vehicles will be traveling too fast to negotiate the exit geometry and may crash into the splitter island or into oncoming traffic in


the adjacent approach lane. Likewise, the exit path radius should not be significantly greater than the circulating path radius to ensure low speeds at the downstream pedestrian crossing.

The exit curve is designed to be curvilinearly tangential to the outside edge of the circulatory roadway. Likewise, the projection of the inside (left) edge of the exit roadway should be curvilinearly tangential to the central island. Figure 8‐99 shows a typical exit layout for a single‐lane roundabout.

Figure 8‐98. Vehicle Path Radii


Figure 8‐99. Typical Roundabout Exit Geometry

8.12.10.1 Exit Curves at Single‐lane Roundabouts At single‐lane roundabouts in urban environments, exits should be designed to enforce a curved exit path with a design speed below 40 km/h in order to maximize safety for pedestrians crossing the exiting traffic stream. Generally, exit radii should be no less than 15m.

In rural locations where there are few pedestrians, exit curvature may be designed with large radii, allowing vehicles to exit quickly and accelerate back to traveling speed. This, however, should not result in a straight path tangential to the central island because many locations that are rural today become urban in the future. Therefore, it is recommended that pedestrian activity be considered at all exits except where separate pedestrian facilities (paths, etc.) or other restrictions eliminate the likelihood of pedestrian activity in the foreseeable future.

8.12.10.2 Exit Curves at Double‐lane Roundabouts As with the entries, the design of the exit curvature at double‐lane roundabouts is more complicated than at single‐lane roundabouts.

8.12.11 Vertical Considerations Elements of vertical alignment design for roundabouts include profiles, superelevation, approach grades, and drainage.

8.12.11.1 Profiles The vertical design of a roundabout begins with the development of approach roadway and central island profiles. The development of each profile is an iterative process that involves tying the elevations of the approach roadway profiles into a smooth profile around the central island.


Generally, each approach profile should be designed to the point where the approach baseline intersects with the central island. A profile for the central island is then developed which passes through these four points (in the case of a four‐legged roundabout). The approach roadway profiles are then readjusted as necessary to meet the central island profile. The shape of the central island profile is generally in the form of a sine curve. Examples of how the profile is developed can be found in Figures 8‐100, 8‐101 and 8‐102 which consist of a sample plan, profiles on each approach, and a profile along the central island, respectively. Note that the four points where the approach roadway baseline intersects the central island baseline are identified on the central island profile.

Figure 8‐100. Sample Plan View


Figure 8‐101. Sample Approach Profile

Figure 8‐102. Sample Central Island Profile

8.12.11.2 Superelevation As a general practice, a cross slope of 2% away from the central island should be used for the circulatory roadway. This technique of sloping outward is recommended for four main reasons:

• It promotes safety by raising the elevation of the central island and improving its visibility;


• It promotes lower circulating speeds;

• It minimizes breaks in the cross slopes of the entrance and exit lanes; and

• It helps drain surface water to the outside of the roundabout.

The outward cross slope design means vehicles making through and left‐turn movements must negotiate the roundabout at negative superelevation. Excessive negative superelevation can result in an increase in single‐vehicle crashes and loss‐of‐load incidents for trucks, particularly if speeds are high. However, in the intersection environment, drivers will generally expect to travel at slower speeds and will accept the higher side force caused by reasonable adverse superelevation.

Figure 8‐103 provides a typical section across the circulatory roadway of a roundabout without a truck apron. Figure 8‐104 provides a typical section for a roundabout with a truck apron. Where truck aprons are used, the slope of the apron should be 3 to 4 percent; greater slopes may increase the likelihood of loss‐of‐load incidents.

Figure 8‐103. Typical Circulatory Roadway Section

Figure 8‐104. Typical Section with a Truck Apron

8.12.11.3 Locating Roundabouts on Grades It is generally not desirable to locate roundabouts in locations where grades through the intersection are greater than four percent. The installation of roundabouts on roadways with grades lower than three percent is generally not problematic. At locations where a constant grade must be maintained through the intersection, the circulatory roadway may be constructed on a constant‐slope plane. This means, for instance, that the cross slope may vary from +3 percent on the high side of the roundabout (sloped toward the central island) to ‐3 percent on the low side (sloped outward). Note that central island cross slopes will pass through level at a minimum of two locations for roundabouts constructed on a constant grade.


Care must be taken when designing roundabouts on steep grades. On approach roadways with grades steeper than ‐4 percent, it is more difficult for entering drivers to slow or stop on the approach. At roundabouts on crest vertical curves with steep approaches, a driver’s sight lines will be compromised, and the roundabout may violate driver expectancy. However, under the same conditions, other types of at‐grade intersections often will not provide better solutions. Therefore, the roundabout should not necessarily be eliminated from consideration at such a location. Rather, the intersection should be relocated or the vertical profile modified, if possible.

8.12.11.4 Drainage With the circulatory roadway sloping away from the central island, inlets will generally be placed on the outer curb line of the roundabout. However, inlets may be required along the central island for a roundabout designed on a constant grade through an intersection. As with any intersection, care should be taken to ensure that low points and inlets are not placed in crosswalks. If the central island is large enough, the designer may consider placing inlets in the central island.

Normal cross slopes for drainage on roundabouts should not exceed 2%. To avoid ponding, longitudinal edge profiles should be graded at not less than 0.5%.

8.12.12 Visibility

8.12.12.1 Eye and Object Heights Visibility to the left and across the central island of a roundabout should be obtainable from a driver's eye height of 1.05m to an object height of 1.05m, and the envelope of visibility should extend to 2.4m above the road surface. It is therefore the same envelope as for Passing Sight Distance. All other visibilities should be assessed in accordance with the envelope for Stopping Sight Distance set out in Figure 8‐1.

Where signs are to be erected on a median, verge or deflection island within the envelope of visibility, including to the left, the mounting height should not be less than 2.4m above the pavement surface, and the envelope needs to be carefully checked on sites where there are significant changes of grade.

8.12.12.2 Visibility on the Approach On the approach to a roundabout, normal Stopping Sight Distance (SSD) applies, in accordance with the appropriate design speed, as described in Section 4 of this manual. The SSD is measured to the "Give Way" line as shown in Figure 8‐105.


Figure 8‐105. Stopping Sight Distance on Approach to Roundabout

8.12.12.3 Visibility to the Left Drivers of all vehicles at the "Give Way" line should be able to see the full width of the circulating pavement to their left, from the "Give Way" line for an adequate distance "a" (measured along the centerline of the circulating pavement as indicated in Table 8‐60, and shown in Figure 8‐106.

Table 8‐60. Visibility at Roundabouts

Inscribed Circle Diameter(m)

Visibility Distance “a” (m)

Less than 40 Whole Intersection

40 to 60 40

More than 60 to 100 50

More than 100 70

The area which should be able to be seen from the centerline of the inner approach lane for a distance of 15m back from the "Give Way" line is as shown in Figure 8‐107.


These requirements apply to all roundabouts, including those with parapets on either side of the circulating pavement. A check should also be made to ensure that the combination of cross slopes and longitudinal grades does not restrict visibility.

Figure 8‐106. Visibility to the Left from the “Give Way” Line

Figure 8‐107. Visibility to the Left over the 15m before the Give Way Line

8.12.13 Entry Curbing On uncurbed approach roads with or without shoulders, care should be taken when introducing the curbs at the roundabout. Normally, the curb should be introduced at the back of the shoulder, with the


shoulder running out as a smooth curved length at an average rate not exceeding 1:10. Figure 8‐108 and 8‐109 show typical arrangements for undivided and divided roads.

Figure 8‐108. Shoulder Run‐out on an Undivided Road

Figure 8‐109. Shoulder Run‐out on a Divided Road

8.12.14 Safety at Roundabouts Roundabouts generally have a lower accidents rate than signalized intersections handling similar traffic flows. The severity of accidents at roundabouts is also considerably lower than at other types of intersection.


The factor which has the greatest influence on safety at roundabouts is vehicle speed, at the entry or within the roundabout. Geometric features that can have a major contributor effect in causing excessive entry and circulating speeds are:

• Inadequate entry deflection

• A very small entry angle which encourages fast merging maneuvers with circulating traffic

• Poor visibility to the "Give Way" line

• More than four entries, necessitating a large roundabout configuration

Additional safety aspects to be considered when designing a roundabout layout include:

• Visibility to the left at entry: This has comparatively little influence upon accident risk; there is nothing to be gained by increasing visibility above the recommended level.

• Crest Curves: Roundabouts should not be sited on crest curves, as this impairs forward visibility and driver comprehension.

• Speeds: A design which encourages entry to the roundabout at low speed and which enables drivers to accelerate steadily on exit contributes significantly to safety, allowing the intersection to be left clear for following road users. This can be achieved by adopting smaller curb radii on entry and larger curb radii on exit.

In urban areas, when approach speeds are low, a ring of contrasting paving can be laid in a chevron pattern inside the central island perimeter at a gentle slope, to aid roundabout visibility.

The provision of yellow Rumble Strips, in association with the advance signing for a roundabout may be beneficial on fast approaches. In other countries, accident reductions of more than 50% have been reported from similar markings.

JUNE 2009 REVISION NO. 02 FLEXIBLE Pavement Design Manual 9‐1

9 Flexible Pavement Design Manual

9.1 Purpose The objective of this manual is to provide a Pavement Design Engineer with sufficient information so that the necessary input data can be developed and proper engineering principles applied to design a new flexible pavement, or develop a properly engineered rehabilitation project. This design manual addresses methods to properly develop a rehabilitation project, pavement milling, and the computations necessary for the pavement design process.

It is the responsibility of the Pavement Design Engineer to insure that the designs produced conform to HIB policies, procedures, standards, guidelines, and good engineering practices.

9.2 General The standards in this manual represent minimum requirements, which must be met for flexible pavement design for new construction and pavement rehabilitation of HIB projects. Any variances should be documented in project files.

Pavement design is primarily a matter of sound application of acceptable engineering criteria and standards. While the standards contained in this manual provide a basis for uniform design practice for typical pavement design situations, the designer must also apply sound engineering judgment.

9.3 References The design procedures incorporated in this document are based on American Standards. See Section 9.12 at the end of this manual for the references.

9.4 Design Considerations Because pavement life is substantially affected by the number of heavy load repetitions applied, a poorly‐designed pavement will not be evident until several years after construction. To design a pavement structure properly, the designer must rely on his own expertise as well as that of soils and planning engineers. Considerations include:

1. Evaluate existing pavement to determine appropriate strategy, value of existing materials or structure for new pavement, and the reasons for its present condition. Check with maintenance forces for history of roadway performance, groundwater problems and other background information;

2. Evaluate subgrade for drainage characteristics and bearing capacity;

3. Make structural calculations. After selecting the appropriate preliminary rehabilitation strategy, the traffic, soils, and pavement materials data must be used to calculate specific pavement layer requirements;

4. Compare feasible alternatives (new pavement, recycling, overlay, etc.) and select the most economically‐sound method for construction;


5. Set specifications. The pavement materials, construction methods, and finished project requirements must be both practical to attain and clearly defined. The designer must ensure that the plans, standard specifications, supplemental specifications, and special provisions clearly and unambiguously define the requirements.

9.5 Pavement Types This manual outlines the design methods for flexible pavement (bituminous concrete). A flexible pavement consists of three layers ‐ subbase (foundation), base, and surface. The subbase consists of granular material ‐ gravel, crushed stone, or a combination. The base consists of a coarse bituminous concrete mixture ("black base"). The surface consists of two courses of bituminous concrete, each with a different consistency ‐ binder material and surface material.

9.6 Definitions and Abbreviations Equivalent 80 kN Load ‐ The conversion of mixed vehicular traffic into its equivalent single‐axle,

80 kN Load. The equivalence is based on the relative amount of pavement damage.

Daily Equivalent 80 kN Load (T80) – The average number of equivalent 80 kN loads which will be applied to the pavement structure in one day. Normally, a 20year design period is used to determine the daily load. (See Table 9.1)

Table 9.1: EQUIVALENT 80 kN AXLE APPLICATIONS PER 1000 TRUCKS FLEXIBLE PAVEMENTS (ESAL)

Highway Class ESAL

Freeways/Expressways 1000

Major Arterial 800

Minor Arterial (Urban) 800

Minor Arterial (Rural) 600

Collector (Urban) 800

Collector (Rural) 600

Local Roads 600

Equivalent 80 kN Axle Applications per 1000 Trucks and Combinations – A factor which reflects the relative mix of sizes and weights of trucks on various classes of highways (e.g., interstate, major primary, and city streets.) Truck percentages provided by Planning exclude two‐axle, four‐tire pickup trucks, the effect of which may be ignored.


Serviceability Index – A measure of a pavement's ability to serve high‐speed, high‐volume automobile and truck traffic on a scale of 0 to 5. It reflects the extent of pavement distress.

Terminal Serviceability Index (Pt) – A pavement design factor which indicates the acceptable pavement serviceability index at the end of the selected design period (usually 20 years). HIB designs for a terminal serviceability (Pt) equal to 2.5.

Bearing Ratio ‐ The load required to produce a certain penetration using a standard piston in a soil, expressed as a percentage of the load required to force the piston the same depth in a selected crushed stone. The test procedures for the California Bearing Ratio (CBR) are used.

Design Bearing Ratio (DBR) – The selected bearing ratio used to design the pavement. It is based on an evaluation of the CBR test results on the soil samples.

Soil Support Value (SSV) – An index of the relative ability of a soil or stone to support the applied traffic loads. It is specifically used for the pavement design method in the AASHTO Interim Guide for Design of Pavement Structures. The soil support value of the subgrade is related to its CBR (DBR).

Structural Number (SN) – A measure of the structural strength of the pavement section based on the type and thickness of each layer within the pavement structure

Layer Coefficient – The relative structural value of each pavement layer per millimeter of thickness. It is multiplied by the layer thickness to provide the contributing SN for each pavement layer.

9.7 Pavement Design Process All pavement designs are determined by the Project Design Engineer with the HIB Engineer, reviewing and approving all pavement designs. The major tasks in the design process are:

9.7.1 Collect Basic Project Data The designer must collect the basic project data such as existing and proposed project plans and profiles, traffic data, existing pavement structure, and field inspection and report.

A. Project Plans and Profiles (Existing & Proposed) These shall be submitted to the HIB Engineer.

B. Traffic Data The traffic data includes:

1. Current ADT (Average Daily Traffic), (ADT for year of proposed opening to traffic) 2. Projected ADT (20 years) 3. ADT truck percentage 4. Number of lanes 5. Divided/undivided, and 6. Source of traffic data

Enter these data on the pavement design checklist.


C. Existing Pavement Structure The thickness and type of each pavement layer (i.e., surface, binder, base, and subbase) shall be recorded; it is especially necessary for overlay and recycling projects.

D. Field Inspection Report The report shall include the general condition of the roadway such as cracking (type, amount) rutting, rideability, and any other characteristic that may be pertinent to the selection of pavement type and scope of work. This should include specific discussions with HIB and/or municipal maintenance and engineering forces.

9.7.2 Determine the Preliminary Scope of Work The design engineer will determine the scope of work for the pavement design. This can be a new pavement, reconstructed pavement, pavement overlay, or a combination of any two. All or part of an existing pavement may be recycled as part of the pavement design. The designer should use the pavement design checklist to document the reasons for the decision.

A. New Pavement A new pavement is a pavement structure which is placed on a previously undisturbed subgrade. It applies to a highway on new location, to a relocated highway, or to the new part of a widened highway.

B. Reconstructed Pavement A reconstructed pavement is one which results when an existing pavement structure is completely removed to the subgrade and replaced with a new pavement structure. This type of work is needed when the existing pavement has deteriorated to such a weakened condition that it cannot be salvaged with corrective action. The type and extent of pavement distress will determine when pavement reconstruction is necessary.

C. Recycled Pavement A recycled pavement results when an existing pavement structure (from which all or part of the pavement is removed on or off site), is combined with new materials and replaced. Recycling is performed in conjunction with a pavement overlay or reconstructed pavement. All proposed recycling projects must be economically justified.

D. Pavement Overlay A pavement overlay consists of placing the needed thickness of bituminous concrete on an existing pavement. The overlay will return the pavement to a high level of serviceability and provide the necessary structural strength for the pavement design period.

9.7.3 Friction A pavement may not require any corrective work other than the application of a friction course because of low skid resistance. In some instances a friction course may be placed or new or reconstructed pavements. A Materials Engineer makes periodic skid measurements of all highways and will check the skid resistance of any facility upon request. The Materials Engineer submits all skid data to Highway Design. The friction course does not add to the structural integrity of the pavement. It is 25 mm thick


and in many cases it is placed on a dense graded binder course about 45 mm in thickness. This ensures a better adhesion between the binder and friction courses.

9.7.4 Widening and Corrective Work to the Existing Pavement A. A pavement may be reconstructed without any additional work or the reconstruction may

include widening, shoulders, extra lanes, etc., in addition to the new pavement structure. B. A recycling project may consist simply in improving the pavement structure by one of the many

methods of recycling; other recycling projects may include the addition of shoulders, widening, etc. The type of work required is to be considered when selecting the methods or type of recycling.

C. An overlay may be placed on the existing surface without any other work except that related to the overlay. An overall pavement rehabilitation project (widening, additional lanes, improved geometry etc.) usually includes an overlay. In many cases a certain amount of corrective work may be required prior to the placing of an overlay. This work may consist of strengthening weakened subgrade where indicated, removing and replacing badly‐deteriorated surface areas, placing a leveling course filling ruts and depressions. Include also any operations that will minimize reflective cracking.

9.7.5 Determine DBR Section 9.7.8 and Table 9.2 discuss the procedure for determining the course of action for selecting a DBR value.

9.7.6 Submit All Pavement Design Information The designer will submit all applicable information for the pavement design to the HIB Engineer. This will include:

1. The pavement design checklist documenting the reasons for selecting the scope of work (see Figure 9.1).

2. The DBR value. 3. A set of project plans and profiles. 4. Traffic data.

9.7.7 HIB Reviews Scope of Work The HIB Engineer will review the designer's recommendation for scope of pavement work and the pavement design checklist documenting the reasons.

9.7.8 HIB Reviews DBR Determination The HIB Engineer will review the designer's determination of the subgrade DBR for approval. If necessary, the Materials Engineer will make a DBR determination, See 9.7.9.


Table 9.2: DESIGN BEARING RATIO (DBR) DETERMINATION

Value From Line (h) of Data Sheet 1 (T 80)

Action

T 80 < 15 Use Minimum Design (See Table 1.3)

15 < T 80 < 120 Assume DBR based on Soil

Classifications from Table 1.3

T 80 > 120 Materials Engineer will determine

DBR

Table 9.3: DBR BASED ON AASHTO SOIL CLASSIFICATION

* Consult HIB Engineer

** Consider Economics of Replacing Poor Material


Figure 9.1 ‐ Pavement Design Checklist


Figure 9.1 ‐ Pavement Design Checklist (Continued)


9.7.9 Request Lab Analysis from Materials Lab If the designer has recommended a lab analysis to determine the DBR and the HIB Engineer have concurred, the designer will submit a request to the Materials Engineer. The procedure is:

1. The Materials Engineer determines the required number of test pits, their locations, and the highest bottom pit elevations.

2. The designer stakes the test pit locations and makes arrangement for sampling by a boring contractor.

3. An engineer must direct the sampling operation, supervise the excavations, and review the test pit logs.

4. The test pit samples must weigh at least 22 kg. When the sample is graded in the laboratory, the lab must follow the procedures prescribed by the Materials Engineer. The designer forwards all samples, gradations, tabulations, and test pit logs to the Materials Engineer.

5. The Materials Engineer will determine the DBR. The report will be sent to the HIB Engineer.

9.7.10 Use DBR from Previous Work If it is available and still applicable, the DBR for the original pavement design or any previous pavement overlays will be used.

9.7.11 Review and Analysis of the Data Submitted The HIB Engineer will notify the design engineer of the results of his review. This step applies to both new/reconstructed pavement and pavement overlays. He may approve, disapprove, request modifications, or request additional information from the design engineer. If applicable, he will also provide the DBR determined by the Materials Engineer.

9.7.12 Design Engineer Conducts Pavement Design Analysis The design engineer will conduct the detailed analysis to determine the type and thickness of each layer in the pavement structures. The types of analysis are discussed in Section 9.7.13, 9.7.14 and 9.7.15.

9.7.13 New/Reconstructed Pavement On new and reconstructed pavements, the designer will determine the detailed full‐depth design of the pavement. The detailed procedure is discussed in Section 9.7.8. Recycling may be considered.

9.7.14 Pavement Overlays On pavement overlays, the designer will specify the depth of the bituminous concrete overlay. The detailed procedure is discussed in Section 9.7.9. In addition, the designer will determine the corrective work needed on the existing pavement.

9.7.15 Combination (Pavement Overlay with Widening) This type of work will require a combination analysis. Section 9.7.8 will determine the full‐depth design of the widened section. Section 9.7.9 will determine the needed depth of overlay.

9.7.16 Submit Pavement Design Recommendation to HIB Engineer The design engineer will submit the recommended detailed pavement design with completed data sheets to the HIB Engineer.


9.7.17 Reviews and Approves The HIB Engineer will review the pavement design recommendation from the design engineer. He may approve, disapprove, modify, or request additional information from the design engineer. The HIB Engineer will notify the design engineer of his action.

9.8 New and Reconstructed Pavement HIB uses the AASHTO Interim Guide for Design of Pavement Structures as the basic design methodology. However, HIB has incorporated several modifications to the Guide's procedures to reflect specific conditions in Libya and to simplify the procedure. This section specifies the HIB procedure for determining the detailed design of a new or reconstructed pavement. This procedure applies to bituminous concrete pavements only.

The HIB procedure follows:

PAVEMENTS DESIGN COVER SHEET

The following must be recorded:

1. Enter the project identification data at the top of the cover sheet. 2. Summarize the recommended pavement design by documenting the surface, base, and subbase

data. List the depths, type of layer and recommended lifts.

DATA SHEET 1: PAVEMENT STRUCTURAL DESIGN DATA

Line (a): Enter the anticipated (current) ADT for date of opening.

Line (b): Enter the future ADT, usually for 20 years beyond the projected opening date. Generally the design period for pavements is 20 years; however there may be occasions when the traffic submitted does not cover the design period. In these cases, the future ADT is to be estimated by approved methods. Under certain circumstances, pavements may be designed for periods of less than 20 years. 3R projects may be designed for periods of 5 to 10 years.

Line (c): Calculate the average ADT during the design period.

Line (d): Calculate the average ADT in one direction.

Line (e): Enter the truck percentage for the ADT.

Line (f): Calculate the average daily truck volume in one direction.

Line (g): Enter the equivalent 80 kN axle application per 1000 trucks and combinations.

See Table 9.1.

Line (h): Calculate the number of 80 kN axle loads per day in one direction (T80).


DESIGN BEARING RATIO (DBR) DETERMINATION

Use the value on Line (h)(T80) and Table 9.2 to determine the subgrade DBR. As noted in Table 9.2, the Materials Engineer may be required to provide the DBR. In all cases, designers make a general computation of the subgrade DBR for reviews by the HIB Engineer.

DATA SHEET 2: DETERMINING STRUCTURAL NUMBER (SN)

Step 1: Determine the design lane equivalent daily 80 kN applications based on the number of lanes.

Step 2: Determine the DBR for the subgrade from Tables 9.2 and 9.3. The subbase DBR is 40 for the typical subbase on new or reconstructed pavements (gravel).

Step 3: Determine the soil support value (SSV). Figure 9.2 illustrates the relationship between the DBR and SSV.

Step 4: Determine the required structural number (SN) above the subbase and above the subgrade. Figure 9.3 should be used. Use the design‐lane T80 from Step 1 for the daily equivalent 80 kN single axle load. Use the SSV from Step 3 for the soil support value.

Step 5: Increase the SN by 15% to determine the design SN to adjust for climatic and other environmental conditions.


Figure 9.2 ‐ DBR vs. SSV


Figure 9.3 – Structural Number (SN) Monograph (For Flexible Pavement P = 2.5)


DATA SHEET 3: PAVEMENTS STRUCTURAL NUMBER (SN)

By trial and error, the designer will select the most cost‐effective design that provides the required SN for the highway conditions. The designer should also consider minimum and maximum lift thicknesses and the logistics of construction procedures when designing the pavement design combinations using this procedure.

Step 1: Select each pavement layer component and the thickness of each layer.

Step 2: From Table 9.4 select the layer coefficient for each pavement layer.

Step 3: Determine the contributing SN for each pavement layer by multiplying the layer coefficient by its thickness.

Step 4: The minimum thicknesses of each layer are noted on Table 9.5.

Step 5: Check to ensure that the required SN is provided above the subbase and the subgrade. If not, increase the layer thickness as necessary. If the trial design exceeds the required SN, reduce the layer thicknesses.

Table 9.4: LAYER COEFFICIENTS FOR NEW AND RECONSTRUCTED PAVEMENTS

Placement Component Layer Coefficient per mm

Surface Course:

Bituminous Concrete

Riding Surface and Binder

1.73 x 10‐2

Base Course:

Bituminous Concrete

1.34 x 10‐2

Subbase:

Crushed Stone (Dense Graded)

Gravel

0.55 x 10‐2

0.43 x 10‐2

Step 6: Determine several alternate pavement designs which satisfy the SN requirements. The selected design will be based on economics.

Step 7: Regardless of the calculations from the pavement design analysis, the minimum design thickness should not be less than those shown in Table 9.5.


Table 9.5: MINIMUM PAVEMENT THICKNESS (New and Reconstructed Flexible Pavements)

The above table is only valid when the conventional design calculations indicate a required pavement structure less than the above. All pavement thickness shall be designed as detailed here. The use of crushed stone as part of the base course makes a firmer base for the paving machines and reduces the amount of gravel required. Gravel gives a structural support (though it is weaker than crushed stone), and provides better drainage.

Figure 9.4 presents the pavement design cover sheet and data sheets 1 to 3.


PAVEMENT DESIGN

NEW AND RECONSTRUCTED PAVEMENT

Shabiya/City ______________________________ Roadway ______________________________

No. of Lanes ______________________________ Highway System ________________________

From Station ______________________________ To Station _____________________________

Date Pavement Designed ____________________ Project Designer ________________________

RECOMMENDED PAVEMENT STRUCTURE

Surface: ________________________________________________________________

________________________________________________________________

________________________________________________________________

Base: ________________________________________________________________

________________________________________________________________

________________________________________________________________

________________________________________________________________

Subbase: ________________________________________________________________

________________________________________________________________

________________________________________________________________

________________________________________________________________

Special Borrow: ________________________________________________________________

Figure 9.4: NEW AND RECONSTRUCTED PAVEMENT


DATA SHEET 1: PAVEMENT STRUCTURAL DESIGN DATA




Current ADT ______________________________ Date ___________________________

Terminal Serviceability Index (T.S.I) = 2.5

(a) Day of Opening A.D.T (Date _______________)* ____________

(b) Future A.D.T (Date (a) + 20 years)** ____________

(c) Mean A.D.T = (a) + (b) ____________

2

(d) Mean A.D.T in One Direction = (c) ____________

2

(e) A.D.T Truck Percentage (“T” A.D.T) ____________

(f) Mean Truck A.D.T in One Direction (d) x (e) ____________

(g) Equivalent 80 kN Axle Application per 1000 Trucks and

Combinations (See Table 1.1) ____________

(h) Number of 80 kN Axle Loads per Day in One Direction

(f) + (g)

1000

(T80) ____________

Comments: _________________________________________________________________________

___________________________________________________________________________________

* Anticipated traffic when facility is opened for travel.

** Under certain conditions this may change to a layer or shorter period.

Figure 9.4: (Continued) NEW AND RECONSTRUCTED PAVEMENT


DATA SHEET 2: DETERMINATION OF STRUCTURAL NUMBER (SN)

Design Lane Equivalent Daily 80 kN Applications (T80)

For 2‐Lane Undivided Highway

Design Lane T80 = 1.00 x Total T80* = 1.00 x _________ = ______________________________

For 4‐Lane (Total Lanes) Divided Highway


Design 6 or More Lanes (Total Lanes) Divided Highway


Design DBR Table 1.2 & 1.3

Subbase…………..DBR = ________________ SSV = ________________

Subgrade………….DBR = ________________ SSV = ________________

Design Structural Number (SN)

Apply Design SSV and Design Lane T80 from above to Design Nomograph (Figure 1.3)

From Fig. 1.3 +15%

Above Subbase…………. = ________________ ________________

Above Subgrade………… = ________________ _________________

* From Line (h) of Data Sheet 1.

Figure 9.4: (Continued) NEW AND RECONSTRUCTED PAVEMENTS


DATA SHEET 3: DETERMINATION OF STRUCTURAL NUMBER (SN)

SN = D1a1 + D2a2 + D3a3

Surface

Material: ……………………………….. D1a1 = ……………………………. = _________________

Base Course

Material: ……………………………….. D2a2 = ……………………………. = _________________

Total SN above Subbase …………………………. = _________________

Subbase (Foundation)

Material: ……………………………….. D3a3 = ……………………………. = _________________

……………………………….. D3a3 = ……………………………. = _________________

Total SN above Subbase …………………………. = _________________

Where: D1 = Surface Thickness, mm

D2 = Base Thickness, mm

D3 = Subbase Thickness, mm

a1 = Coefficient of Relative Strength, Surface

a2 = Coefficient of Relative Strength, Base

a3 = Coefficient of Relative Strength, Subbase

Comments: _________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________________

___________________________________________________________________________________

Figure 9.4: (Continued) NEW AND RECONSTRUCTED PAVEMENTS


SAMPLE


Example

Given: Approximately 1800 meters of Broadway Street (Route 107) is being reconstructed in Revere. Broadway is a two‐lane urban facility. The following data is given:

1995 ADT = 21640 2015 ADT = 22480 T (ADT) = 5%

Problem: Determine the pavement structural design for a 20‐year design period.

Solution: Data Sheet 1

Lines (a) to (g) on Data Sheet 1 are completed as instructed. Table 9.1 is used to select the equivalent 80 kN axle applications per 1000 trucks and combinations. The urban roads value of 800 is used and entered on Line (h). Therefore, Line (j) is 440.

DBR Determination

Line (j) (T80) exceeds 120. Therefore, according to Table 9.2, Materials Engineer must determine the DBR for the subgrade. This will be processed by the Design Engineer as described in Section 9.7.

Data Sheet 2

Step 1: The design lane equivalent for a two‐lane undivided highway is 1.00 x Line (j) which, in this case, is 440.

Step 2: Materials Engineer determines that the subgrade DBR is 9.

Step 3: Using Figure 9.3, the subgrade SSV = 4.2; the subbase SSV = 7.8.

Step 4: Using Figure 9.4, the required SN above the subbase is 2.6; above the subgrade it is 4.15.

Step 5: Increasing these values by 15% yields SN design values of 2.99 and 4.77.

Data Sheet 3

Use the trial‐and‐error procedure to determine the most economical design which satisfies the SN requirements for the subbase and subgrade. The following design is selected:

90 mm bituminous concrete surface 115 mm bituminous concrete base 100 mm dense graded crushed stone 255 mm gravel A completed summary sheet and completed data sheets are shown.


9.9 Pavement Overlays A pavement overlay can be used if the designer determines that an existing pavement is in reasonably good condition. As discussed in Section 9.7, a pavement overlay may be in conjunction with roadway widening and/or corrective work to the existing pavement. The depth of bituminous concrete overlay will be determined by the following procedure:

Pavement Overlay Design Cover Sheet

The following must be recorded:

1. Enter the project identification data at the top of the cover sheet. 2. Document the existing pavement structure before overlay. 3. Record the recommended pavement overlay thickness.

Data Sheet 1: Pavement Structural Design Data

Line (a): Enter the current ADT

Line (b): Enter the future ADT, usually for 20 years beyond the current. (Note: The traffic data for the Master Planning and Development may not correspond to the dates in Lines (a) and (b). If not, the designer should assume a uniform straight‐line increase between the data. This assumption can then be used to determine the traffic volumes in Lines (a) and (b).)

Line (c): Calculate the average ADT during the design period.

Line (d): Calculate the average ADT in one direction.

Line (e): Enter the truck percentage for the ADT.

Line (f): Calculate the average daily truck volume in one direction.

Line (g): Enter the equivalent 80 kN axle applications per 1000 trucks and combinations. See Table 9.1.

Line (h): Calculate the number of 80 kN axle loads per day in one direction.

Line (j): Calculate the design lane equivalent daily 80 kN applications based on number of lanes.

Line (k): Enter the subgrade DBR and SSV. These will be provided by the Design Engineer as discussed in Section 9.7 and Tables 9.2 and 9.3.

Line (l): Determine the required SN above the subgrade from Figure 9.3.

Line (m): Determine the design SN by increasing the SN by 15%.

Data Sheet 2: Actual SN of Existing Pavement

Line (a): Enter the SSV of the existing pavement elements. The SSV for the penetrated crushed stone base, the sand bound crushed stone base, and the gravel subbase are usually assumed as


shown. However, if laboratory‐determined DBR results are available, these values should be used. Enter the SSV for the subgrade from Line (k) of Data Sheet 1.

Line (b): Determine the SN of the existing pavement. Follow these steps:

1. Table 9.6 provides the layer coefficient for each layer component for a new pavement. 2. The coefficients in Table 9.6 should be multiplied by a reduction factor (RF) from Table

9.7. The RF will be based on a visual survey of the type and extent of distress in the existing pavement. The RF will apply even if corrective work is performed on the existing pavement.

3. The contributing SN for each layer is calculated by multiplying its depth by the layer coefficient and RF.

4. The total SN is found by summing the SN of each pavement layer. (Note: If Portland cement concrete is part of the existing pavement, the PDE will

determine its contributing SN.)

Line (c): Determine the actual SN above each layer of the existing pavement. The SN for each layer is entered in the appropriate column. The "Total SN" reflects the cumulative SN above each pavement layer.

Data Sheet 3: Determination of Overlay Thickness

Line (a): Determine the required SN above each layer of the existing pavement using Figure 9.4. The values from Line (j) on Data Sheet 1 and from Line (a) of Data Sheet 2 are used in the figure. The SN values from Figure 9.4 are increased by 15% to determine the design SN.

Line (b): Determine the SN deficiency for each layer for the existing pavement. The required SN from Line (a) of Data Sheet 3 is entered in the first column. Enter the value from Line (c) of Data Sheet 2 in the second column. The first column SN minus the second column SN yields the SN difference, which is entered in the third column. (Note: A negative value indicates there is no SN deficiency for that pavement layer.)

Line (c): The largest SN deficiency from the table in Line (b) is used to determine the thickness of the pavement overlay. The 1.73 x 102 is in the SN value per mm for bituminous concrete surface course. Regardless of the calculation, the minimum overlay thickness is 45 mm.

Figure 9.5 presents the pavement overlay design cover sheet and data sheets 1 to 3.


Table 9.6: LAYER COEFFICIENTS FOR EXISTING PAVEMENTS

1. These are the layer coefficient values for when the pavement was new. They must be

reduced according to the Reduction Factors in Table 9.7

Table 9.7: REDUCTION FACTORS FOR EXISTING PAVEMENT

1. This is based on a visual survey of the type and extent of distress. If the pavement distress

and deterioration is worse than described in the table, consideration should be made for the

removal and reconstruction of the pavement.


PAVEMENT OVERLAY DESIGN




Date Pavement Designed ____________________ Project Designer ________________________

EXISTING PAVEMENT ELEMENTS BEFORE OVERLAY

_____________ Bituminous Concrete Surface

_____________ Penetrated Crushed Stone Base

_____________ Sand Bound Crushed Stone Base

_____________ Gravel Subbase

RECOMMENDED OVERLAY THICKNESS

Figure 9.5: PAVEMENT OVERLAY DESIGN


DATA SHEET: PAVEMENT STRUCTURAL DESIGN DATA

Terminal Serviceability Index Nomograph = 2.5

(a) Current A.D.T. (Date _______________) ____________

(b) Future A.D.T. (Date _______________) ____________

(c) Mean A.D.T. = (a) + (b) ____________

2

(d) Mean A.D.T in One Direction (c) ____________

2

(e) A.D.T Truck Percentage ____________

(f) Mean Truck A.D.T in One Direction (d) x (e) ____________

(g) Equivalent 80 kN Axle Application per 1000 Trucks and

Combinations (See Table 1.1) ____________

(h) Number of 80 kN Axle Loads Per Day in One Direction

(f) + (g)

1000

(T80) ____________

(i) 80 kN Load on Design Lane: (h) Z 1.00 for 2 lanes;

(h) x 0.90 for 4 lanes; (h) x 0.80 for 6 or more lanes ____________

(j) Subgrade Design Bearing Ratio and Soil Support Value ____________

(k)* Structural Number (SN) Required Above the Subgrade ____________

(l)* Increase SN by 15% for Design SN ____________

* These values are developed on Data Sheet # 3

Figure 9.5 (Continued)


DATA SHEET 2: ACTUAL SN OF EXISTING PAVEMENT

(a) Soil Support Values of Existing Granular Pavement Elements

Penetrated Crushed Stone Base = ____90____

Sand Bound Crushed Stone Base = __________

Gravel Subbase = ____66____

Subgrade = __________

(b) Actual Structural Number (SN) of Each Layer of Existing Pavement

(1)

Depth Description

(2)

Coefficient

Table 1.6

(3)

RF

Table 1.7

Coefficient

(1)x(2)x(3)

Bituminous Concrete

Surface

Penetrated Crushed Stone

Base

Sand Bound Crushed Stone

Base

Gravel Subbase

Total SN =

Figure 9.5: (Continued) PAVEMENT OVERLAY DESIGN


(c) Actual Structural Number (SN) Above Each Layer of Existing Pavement

Above Top of:

SN*

Bituminous Concrete

SN*

Penetrated

Stone

SN*

Sand‐Bd.

Stone

SN*

Gravel

Total

SN**

Penetrated Crushed Stone Base

Sand Bound Crushed Stone Base

Gravel Subbase

Subgrade

* From Table (b) Above

** Accumulated SN Values from Layers Above

Figure 9.5: (Continued) PAVEMENT OVERLAY DESIGN


DATA SHEET 3: DETERMINATION OF OVERLAY THICKNESS

(a) Required Structural Number (SN) Above Each Layer of Existing Pavement

SN +15%

Above Top of Penetrated Crushed Stone Base = _________________ ___________________

Above Top of Sand Bound Stone Base = _________________ ___________________

Above Top of Gravel Subbase = _________________ ___________________

Above Top of Subgrade = _________________ ___________________

(b) SN Deficiency to be Corrected with an Overlay

Above Top of: Required SN* Actual

SN** SN Difference

Penetrated Crushed Stone Base

Sand Bound Crushed Stone Base

Gravel Subbase

Subgrade

* From (a) Data Sheet #3

** From (c) Data Sheet #2

(c) Thickness of Bituminous Concrete Overlay

Depth = Largest SN Difference = ________________________

0.0173

Figure 9.5 (Continued) PAVEMENT OVERLAY DESIGN


Example

Given: Approximately 750 meters of Route 3 in Hingham is being overlaid. Route 3 is a four‐lane urban facility. The existing pavement exhibits some fine cracking with little deformation in the wheel paths. The following data is given:

1995 ADT = 54 100

2015 ADT = 89 300

T (ADT) = 12%

Existing Pavement:

115 mm bituminous concrete surface

115 mm penetrated crushed stone base

300 mm gravel subbase

Problem: Determine the depth of a bituminous concrete overlay for a 20‐year design period.

Solution:

Data Sheet 1

Line (a) ‐ Line (f): Lines (a) to (f) are completed as instructed.

Line (g): Table 9.1 yields a value of 800.

Line (h): This calculation yields a T80 = 3442.

Line (j): For a four‐lane facility, the design lane load is 0.9 x T80, or 3098.

Line (k): The PDE provides a subgrade DBR of 11, which yields SSV = 4.5.

Line (l): Figure 9.3 yields an SN ‐ 5.35 above the subgrade.

Line (m): Increasing by 15% yields a design SN of 6.15.

Data Sheet 2

Line (a): The subgrade SSV = 4.5 is entered.

Line (b): Table 9.6 is used to select the layer coefficients for the existing pavement. The existing pavement is in generally good condition. Therefore, a reduction factor of 0.9 is selected from Table 9.7. The calculations are shown on the completed data sheet.


Line (c): The actual SN above each pavement layer is entered as shown on the completed data sheet.

Data Sheet 3

Line (a): Figure 9.3 is used to determine the required SN above each layer of the existing pavement. These are increased by 15% as shown.

Line (b): The SN deficiency for each layer of the existing pavement is shown on the completed data sheet.

Line (c): The largest SN deficiency is 2.33 for the subgrade. This is used to determine that a 135 mm overlay is needed to provide acceptable pavement performance over the 20 year period.

A completed summary sheet and completed data sheets follow.

* * * * * * * *


9.10 Recycling "Recycling" means reusing existing paving materials for the rehabilitation and maintenance of pavements. It conserves energy, aggregates, and asphalt. It is important to understand that recycling is not the answer to all paving problems. In order to use the recycling concept to its best advantage, certain criteria relative to the condition and function at the facility must be considered. The HIB Design Engineer will review and must approve all proposed recycling projects. Materials Engineer and the PDE will develop the specifications and structural design for the recycled pavements.

There are three general methods of recycling pavements; these methods are in turn subdivided into sub‐methods. The three general types are described below.

1. SURFACE RECYCLING: This is a process in which the bituminous concrete pavement is reworked by a heater planer, hot milling, heater scarifier, etc. The depth of reworked material is usually about 25 mm; it is done in a continuous operation. The operation may involve the additions of virgin hot mix material and modifiers.

It is effective in reducing some reflective cracking, eliminates some raveling, rutting corrugations etc. The structural improvement is minimal; the heater planer has certain limitations relative to depth of penetration. The "Surface Recycling" method is used infrequently.

2. "IN PLACE SURFACE AND BASE RECYCLING" The existing surface and base are scarified and pulverized, mixed with some gravel subbase material, reshaped, and compacted to form a base. Additives or other agents may be added to this blend. The pulverizing and blending is usually done on the site; however, there is the option of doing the pulverizing and cold blending at a central plant. A top course mix is placed on the compacted material.

The structural capacity is improved, and reflective cracking is eliminated. However, quality control is difficult to maintain. Traffic is disrupted, and the pulverizing equipment breaks down frequently. This is a less expensive operation than a "Central Plant" (hot) reclamation project.

3. CENTRAL‐PLANT RECYCLING This is a process where the reclaimed pavement is combined with new asphalt and aggregate and in some instances the addition of a modifier may be specified. The pavement surface is usually removed with a cold planer or similar type machine to a predetermined depth. The pavement fragments are transported to a "Central Plant" where they are seized and mixed hot as noted above. The finished product, depending on the sizing specification, may be used as a riding surface or binder.

This method of reclamation increases the structural capacity, improves quality control, reduces, and, in most cases, eliminates reflective cracking. Traffic disruption and pollution are significant disadvantages of this type of operation.


9.11 Skid Resistance All pavement designs will include a surface course that provides the necessary skid resistant qualities. It should also retain these qualities during the pavement design period. HIB standard pavement mix design provides the required skid resistance in most instances.

Skid resistance is a function of the pavement surface texture. Surface texture is a combination of fine (or micro‐) texture and coarse (or macro‐) texture. Microtexture is determined by the surface roughness of aggregate particles. The roughness penetrates the water film on the road surface to provide direct contact with the tire. A surface that has good microtexture ensures skid resistance at low speed. Macrotexture is a function of aggregate gradation. It provides passages for water to escape from the tire‐pavement interface, thereby reducing hydroplaning. Macrotexture becomes more important as speed increases. At higher speeds skid resistance is provided by combined effects of microtexture and macrotexture.

The skid number is a measure of skid resistance. The skid number is the coefficient of friction times 100. Thus a pavement with a skid number of 35 has a coefficient of friction of 0.35. The skid number is measured on a wet pavement at a skid tester speed of 64 kph. The skid properties of all highways are monitored by the Materials Engineer.

As noted above, the HIB mix design is such that adequate skid resistance is provided. However, after years of service the skid resistance characteristics may be greatly reduced. When the skid number falls below a certain number, corrective measures must be taken to restore the skid resistance to an adequate level. This is accomplished by placing a friction course on the questionable bituminous concrete surface. The friction course is an open‐graded bituminous concrete mix placed at a depth of about 25 mm. This layer does not contribute to the structural strength of the pavement. It can be subject to raveling at intersections where start and stop activity is frequent; application may not be practical at certain intersections.

Skid resistance may be built into a Portland cement concrete pavement by grooving with metal tines while the concrete is in a plastic state. The skid resistance of cement concrete in service can be increased by mechanical grooving. The grooves may be placed longitudinally or transversely; each method has its advantages and disadvantages. The consensus is that longitudinal grooving is preferable for highways, and transverse grooving is preferable for airports.

The designer should inform the HIB Design Engineer if the skid resistance of a highway is suspect. The HIB Design Engineer will request from the Materials Engineer a skid test of the section in question to be performed.


9.12 References • Interim Guide for Design of Pavement Structures, AASHTO, 1972 (Revised 1981). • Layered Pavement Design Method for Massachusetts, Massachusetts Department of Public

Works and Massachusetts Institute of Technology, January, 1965. • Guidelines for Skid Resistant Pavement Design, AASHTO, 1976 • Asphalt Overlays and Pavement Rehabilitation, MS17; the Asphalt Institute, November, 1969. • Alternatives in Pavement Maintenance, Rehabilitation and Reconstruction, IS178, the Asphalt

Institute, May, 1981.

JUNE 2009 REVISION NO. 02 UNIFORM Traffic Control Devices 10‐1

10 Uniform Traffic Control Devices

All traffic control devices shall be in accordance with the Traffic and Licensing Department of Libya. The Traffic and Licensing Department adopted the requirements of “Manual on Uniform Traffic Control Devices” by Kingdom of Saudi Arabia, Ministry of Communications. This manual should be used for traffic signs, pavement markings, traffic signals, traffic control for work areas, traffic control for school areas, and traffic control for railroad grade crossings. The following additional requirements should be used in traffic control for work areas.

10.1 Traffic Control for Work Area (Supplements) The safety of road users, which include drivers, pedestrians and bicyclists, as well as personnel in work zones, should be an integral and high priority element of every project in the planning, design, construction, and maintenance phases. All projects and works on highways, roads, and streets shall have a traffic management plan. All work shall be executed under HIB approved procedures and shall require approval by CM/CS. This document contains supplemental information to Part 5 of the “Manual on Uniform Traffic Control Devices” by Kingdom of Saudi Arabia (MUTCD) and contains guidelines and standards for the preparation of traffic management plans and for the execution of traffic control in work zones, for construction and maintenance operations and utility work on highways, roads, and streets in all regions of Libya. Typical applications for various situations are provided at the end of this document. Modification can be made to these details as long as the changes comply with design standards set forth in the MUTCD and as required by HIB and the CM/CS. The sign spacing shown on the details is typical (recommended) distances. These distances may be increased or decreased based on field conditions, in order to avoid conflicts or to improve site specific traffic controls.

10.2 ROADWAY CONSTRUCTION

10.2.1 Corridor and Networkwide Constructions Roadway construction can range from a site‐specific construction to corridor construction, and even to an overall network construction program. As work activities are developed at the construction site, they affect the overall corridor construction staging, traffic movements, number of lanes used, utilities, and pedestrian access. To determine the number of lanes to be maintained within the construction zone, it would depend on the existing level of service of the roadway and how that affects the whole corridor function. Also to maintain traffic mobility, alternative roadways or detours can be used to bypass the construction sites. Based on local conditions, the local authority can sacrifice mobility in order to expedite the construction. See Figures 10a – 10d at the end of this document for examples of construction layout plans.

For a network‐wide construction program, various construction projects must be coordinated concurrently and on schedule, as the case here with the ongoing construction projects in all regions of Libya. A key tool for this coordination is the development and implementation of a traffic monitoring system which would include traffic sensors, cameras, variable message signs, and other traffic monitoring tools that can be integrated into a local traffic management system, See Figure 10‐1. The purpose of the traffic monitoring system is to track the traffic conditions and evaluate the impacts of construction throughout the network which will in turn be used in the scheduling and coordinating of other projects to minimize conflicts and maintain a reasonable level of service for both the travelling


public and the pedestrians. A traffic model is essential for simulating traffic conditions in the network construction program based on different scenarios of lane or road closures and their impacts.

10.2.2 Authority A traffic management plan that would address traffic mobility, safety, local and pedestrian access must be enforced by local authorities with jurisdiction over the regulations of the roadway to make sure that the plan is implemented properly. There shall be adequate statutory authority for the implementation and enforcement of needed road user regulations, parking controls, speed zoning, and the management of traffic incidents. Such statutes shall provide sufficient flexibility in the application of Temporary Traffic Control (TTC) to meet the needs of changing conditions in the TTC zone.


Figure 10-1: Network Traffic Management Program


10.3 Traffic Control Zones The primary function of Temporary Traffic Control is to provide for the reasonably safe and efficient movement of road users through or around traffic control zones during project construction while reasonably protecting workers, responders to traffic incidents, and equipment.

Of equal importance to the public traveling through the traffic control zone is the safety of workers, performing the many varied tasks within the work space. Traffic control zones present constantly changing conditions that are unexpected by the road user. This creates an even higher degree of vulnerability for the workers and incident management responders on or near the roadway. At the same time, the traffic control zone provides for the efficient completion of whatever activity interrupted the normal use of the roadway.

The following principles must be applied to temporary traffic control zones:

• Traffic movement should be disrupted as little as possible, with the proper closure, transition, and speed reduction configurations.

• Road users should be guided in a clear and positive manner while approaching and within construction, maintenance, and utility work areas.

• Routine inspection and maintenance of traffic control elements should be performed both day and night.

• Both the Contractor and CM/CS should assign at least one person on each project to have day‐to‐day responsibility for assuring that the traffic control elements are operating effectively and any needed operational changes are brought to the attention of their supervisors.

• The Contractor shall comply with all local police regulations and authorities in Libya for traffic management and traffic control configuration in work zones.

• Special plans preparation and coordination with transit, other highway agencies, law enforcement and other emergency units, utilities, and schools might be needed to reduce unexpected and unusual road user operation situations.

• Contractors of adjacent constructions shall coordinate construction staging, lane closures, and traffic shifting.

• During TTC activities, commercial vehicles might need to follow a different route from passenger vehicles because of bridge, weight, clearance, or geometric restrictions. Also, vehicles carrying hazardous materials might need to follow a different route from other vehicles.

• Traffic management in temporary traffic control zones should be designed on the assumption that road users will only reduce their speeds if they clearly perceive a need to do so, and then only in small increments of speed.

• TTC zones should not present a surprise to the road user. Frequent and/or abrupt changes in geometrics and other features should be avoided. Transitions should be well delineated and


long enough to accommodate driving conditions at the speeds vehicles are realistically expected to travel.

• A Traffic Management Plan (TMP) should be used for a temporary traffic control zone to specify particular traffic control devices and features, or to reference typical drawings such as those contained in this manual. The TMP should start in the planning phase and continue through the design, construction, and restoration phases.

• Applications of speed reduction countermeasures and enforcement can be effective in reducing traffic speeds in temporary traffic control zones.

10.3.1 Application Planned work phasing and sequencing should be the basis for the use of traffic control devices for temporary traffic control zones. This manual should be consulted for specific traffic control requirements and examples where construction or maintenance work is planned.

10.3.2 Guideline General plans or guidelines should be developed to provide safety for motorists, bicyclists, pedestrians, workers, enforcement/emergency officials, and equipment, with the following factors being considered:

• The basic safety principles governing the design of permanent roadways and roadsides should also govern the design of TTC zones. The goal should be to route road users through such zones using roadway geometrics, roadside features, and TTC devices as nearly as possible comparable to those for normal highway situations.

• A TMP, in detail appropriate to the complexity of the work project or incident, should be prepared and understood by all responsible parties before the site is occupied. Any changes in the TMP should be approved by an official knowledgeable (for example, trained and/or certified) in proper TTC practices.

Road user movement should be inhibited as little as practical, based on the following considerations:

• TTC at work and incident sites should be designed on the assumption that drivers will only reduce their speeds if they clearly perceive a need to do so.

• Frequent and abrupt changes in geometrics such as lane narrowing, dropped lanes, or main roadway transitions that require rapid maneuvers, should be avoided.

• Provisions should be made for the reasonably safe operation of work, particularly on high‐speed, high‐volume roadways.

• Road users should be encouraged to use alternative routes that do not include TTC zones.

• Bicyclists and pedestrians, including those with disabilities, should be provided with access and reasonably safe passage through the TTC zone.

• Roadway occupancy should be scheduled during off‐peak hours and, if necessary, night work should be considered.


• Early coordination with officials having jurisdiction over the affected cross streets and providing emergency services should occur before roadway or ramp closings.

Motorists, bicyclists, and pedestrians should be guided in a clear and positive manner while approaching and traversing TTC zones and incident sites. The following principles should be applied:

• Adequate warning, delineation, and channelization should be provided to assist in guiding road users in advance of and through the TTC zone or incident site by using proper pavement marking, signing, or other devices that are effective under varying conditions. Providing information that is in usable formats by pedestrians with visual disabilities should also be considered.

• TTC devices inconsistent with intended travel paths through TTC zones should be removed or covered. However, in intermediate‐term stationary, short‐term, and mobile operations, where visible permanent devices are inconsistent with intended travel paths, devices that highlight or emphasize the appropriate path should be used. Providing traffic control devices that are accessible to and usable by pedestrians with disabilities should be considered.

• Flagging procedures, when used, should provide positive guidance to road users traversing the TTC zone.

To provide acceptable levels of operations, routine day and night inspections of TTC elements should be performed as follows:

• Individuals who are knowledgeable (for example, trained and/or certified) in the principles of proper

• TTC should be assigned responsibility for safety in TTC zones. The most important duty of these individuals should be to check that all TTC devices of the project are reasonably consistent with the TMP and are effective in providing reasonably safe conditions for motorists, bicyclists, pedestrians, and workers.

• As the work progresses, temporary traffic controls and/or working conditions should be modified in order to provide reasonably safe and efficient road user movement and to provide worker safety. The individual responsible for TTC should have the authority to halt work until applicable or remedial safety measures are taken.

• TTC zones should be carefully monitored under varying conditions of road user volumes, light, and weather to check that applicable TTC devices are effective, clearly visible, clean, and in compliance with the TMP.

• When warranted, an engineering study should be made (in cooperation with law enforcement officials) of reported crashes occurring within the TTC zone. Crash records in TTC zones should be monitored to identify the need for changes in the TTC zone.

Attention should be given to the maintenance of roadside safety during the life of the TTC zone by applying the following principles:


• To accommodate run‐off‐the‐road incidents, disabled vehicles, or emergency situations, unencumbered roadside recovery areas or clear zones should be provided where practical.

• Channelization of road users should be accomplished by the use of pavement markings, signing, and crashworthy, detectable channelizing devices.

• Work equipment, workers' private vehicles, materials, and debris should be stored in such a manner to reduce the probability of being impacted by run‐off‐the‐road vehicles.

10.3.3 Traffic Management Plans A TMP describes traffic control measures to be used for facilitating road users through a work zone or an incident area. Traffic management plans play a vital role in providing continuity of reasonably safe and efficient road user flow when a work zone, incident, or other event temporarily disrupts normal road user flow.

TMPs range in scope from being very detailed to simply referencing typical drawings, as shown in this document, and standard approved highway agency drawings and manuals, or specific drawings contained in the contract documents. The degree of detail in the TMP depends entirely on the nature and complexity of the situation. The TMP components would typically include the following:

• General Layout – overall construction sequencing of the project.

• Legends and Abbreviations – To identify the symbols and abbreviations shown on the plans.

• Construction Phasing Plans – detailed construction staging showing work zones, traffic movements, channelizing devices and staging notes.

• Staging Sections – sections showing the work staging and sequencing with emphasis on buffer width, vertical difference, treatment of temporary conditions and safety measures. Staging notes can be shown with the sections or on the phasing plans.

• Temporary Profiles – In some cases, a temporary profile is necessary to meet an interim condition of roadway construction. The profile must be shown with all its geometric values.

• Detour Plans – location plans showing the detours to where traffic is diverted to bypass construction area. The plans include all necessary detour, street names, and arrow signs.

• Miscellaneous Details – details of temporary treatments, special details, and traffic control devices, which can be referenced to in this manual.

Factors that must be considered in the TMP planning and preparation:

• TMPs should be prepared by persons knowledgeable about the fundamental principles of TTC and work activities to be performed. The design, selection, and placement of TTC devices for a TMP should be based on engineering judgment.

• Coordination should be made between adjacent or overlapping projects to check that duplicate signing is not used and to check compatibility of traffic control between adjacent or overlapping projects in terms of lane closure, transition, and traffic shifting.


• Traffic control planning should be completed for all highway construction, utility work, maintenance operations, and incident management including minor maintenance and utility projects prior to occupying the TTC zone. Planning for all road users should be included in the process.

• Provisions for effective continuity of accessible circulation paths for pedestrians should be incorporated into the TTC process. Where existing pedestrian routes are blocked or detoured, information should be provided about alternative routes that are usable by pedestrians with disabilities, particularly those who have visual disabilities.

• Access to temporary bus stops, reasonably safe travel across intersections with accessible pedestrian signals, and other routing issues should be considered where temporary pedestrian routes are channelized. Barriers and channelizing devices that are detectable by people with visual disabilities should be provided.

• Provisions may be incorporated into the project bid documents that enable contractors to develop an alternate TMP.

• Modifications of TMPs may be necessary because of changed conditions or a determination of better methods of safely and efficiently handling road users.

This alternate or modified plan should have the approval of the responsible highway agency prior to implementation.

Provisions for effective continuity of transit service should be incorporated into the TTC planning process because often public transit buses cannot efficiently be detoured in the same manner as other vehicles (particularly for short‐term maintenance projects). Where applicable, the TMP should provide for features such as accessible temporary bus stops, pull‐outs, and satisfactory waiting areas for transit patrons, including persons with disabilities, if applicable.

Reduced speed limits should be used only in the specific portion of the TTC zone where conditions or restrictive features are present. However, frequent changes in the speed limit should be avoided. A TMP should be designed so that vehicles can reasonably safely travel through the TTC zone with a speed limit reduction of no more than 16 km/h.

A reduction of more than 16 km/h in the speed limit should be used only when required by restrictive features in the TTC zone. Where restrictive features justify a speed reduction of more than 16 km/h, additional driver notification should be provided. The speed limit should be stepped down in advance of the location requiring the lowest speed, and additional TTC warning devices should be used.

Reduced speed zoning (lowering the regulatory speed limit) should be avoided as much as practical because drivers will reduce their speeds only if they clearly perceive a need to do so.

10.3.4 Components of Temporary Traffic Control Zones Most TTC zones are divided into four areas: the Advance Warning Area, the Transition Area, the Activity Area, and the Termination Area. Figure 10‐2 illustrates these four areas. These four areas are described in the following sections.

1. Advance Warning Area


The advance warning area is the section of highway where road users are informed about the upcoming work zone or incident area.

The advance warning area may vary from a single sign or high‐intensity rotating, flashing, oscillating, or strobe lights on a vehicle to a series of signs in advance of the TTC zone activity area.

Typical distances for placement of advance warning signs on freeways and expressways should be longer because drivers are conditioned to uninterrupted flow. Therefore, the advance warning sign placement should extend on these facilities as far as 800 m or more.

On urban streets, the effective placement of the first warning sign in meters should range from 0.75 to 1.5 times the speed limit in km/h, with the high end of the range being used when speeds are relatively high. When a single advance warning sign is used (in cases such as low‐speed residential streets), the advance warning area can be as short as 30 m. When two or more advance warning signs are used on higher‐speed streets, such as major arterials, the advance warning area should extend a greater distance.

Since rural highways are normally characterized by higher speeds, the effective placement of the first warning sign in meters should be substantially longer—from 1.5 to 2.25 times the speed limit in km/h. Since two or more advance warning signs are normally used for these conditions, the advance warning area should extend 450 m or more for open highway conditions.

Advance warning may be eliminated when the activity area is sufficiently removed from the road users’ path so that it does not interfere with the normal flow.


Figure 10-2: Component Parts of a Temporary Traffic Control Zone


1. Transition Area

The transition area is that section of highway where road users are redirected out of their normal path. Transition areas usually involve strategic use of tapers, which because of their importance are discussed separately in detail.

When redirection of the road users’ normal path is required, they shall be channelized from the normal path to a new path.

In mobile operations, the transition area moves with the work space.

2. Activity Area

• The activity area is the section of the highway where the work activity takes place. It is comprised of the work space, the traffic space, and the buffer space.

The work space is that portion of the highway closed to road users and set aside for workers, equipment, and material, and a shadow vehicle if one is used upstream. Work spaces are usually delineated for road users by channelizing devices or, to exclude vehicles and pedestrians, by temporary barriers.

The work space may be stationary or may move as work progresses.

Since there might be several work spaces (some even separated by several kilometers or miles) within the project limits, each work space should be adequately signed to inform road users and reduce confusion.

• The traffic space is the portion of the highway in which road users are routed through the activity area.

• The buffer space is a lateral and/or longitudinal area that separates road user flow from the work space or an unsafe area, and might provide some recovery space for an errant vehicle. Neither work activity nor storage of equipment, vehicles, or material should occur within a buffer space.

Buffer spaces may be positioned either longitudinally or laterally with respect to the direction of road user flow. The activity area may contain one or more lateral or longitudinal buffer spaces. A longitudinal buffer space may be placed in advance of a work space.

The longitudinal buffer space may also be used to separate opposing road user flows that use portions of the same traffic lane, as shown in Figure 3.

Typically, the buffer space is formed as a traffic island and defined by channelizing devices.

When a shadow vehicle, arrow panel, or changeable message sign is placed in a closed lane in advance of a work space, only the area upstream of the vehicle, arrow panel, or changeable message sign constitutes the buffer space.


The lateral buffer space may be used to separate the traffic space from the work space, as shown in Figures 2 and 3, or such areas as excavations or pavement‐edge drop‐offs. A lateral buffer space also may be used between two travel lanes, especially those carrying opposing flows.

The width of a lateral buffer space should be determined by engineering judgment.

3. Termination Area

The termination area shall be used to return road users to their normal path. The termination area shall extend from the downstream end of the work area to the last TTC device such as END ROAD WORK signs, if posted.

An END ROAD WORK sign, a Speed Limit sign, or other signs may be used to inform road users that they can resume normal operations.


Figure 10a: Traffic Management Plan (Sample) for 96th Street Station Construction of Second Avenue Subway in NYC


Figure 10b: Traffic Management Plan (Sample) for 96th Street Station Construction of Second Avenue Subway in NYC


Figure 10c: Traffic Management Plan (Sample) for 96th Street Station Construction of Second Avenue Subway in NYC


Figure 10d: Traffic Management Plan (Sample) for Construction Work

JUNE 2009 REVISION NO. 02 LANDSCAPE Design Criteria 11‐1

11 Landscape Design Criteria This section presents standard design criteria for landscape. It has been developed as a way of establishing a baseline, or minimum, for the standard of implementation sought in new developments.

Where appropriate proposals may be presented that provide additional detail, or standards. These will be considered on their merit, but must improve on the criteria herein and meet recognized international standards. Where alternatives are put forward and explanation must accompany the reasons why they are being proposed.

The criteria presented have been developed to reflect typical conditions. Certain situations, climatic conditions, and locations may require modification or interpretation of the criteria herein. In most, if not all instances, the use of appropriate qualified designers, engineers, technicians and other specialists is required as standard.

11.1 Landscape Design Criteria The Developer shall be responsible for landscaping within the project’s site boundaries, including open spaces and for pedestrian (sidewalk) planting areas up to roadside curb with street according to the landscape design criteria described herein.

There will be a presumption that all plants should be directly sourced and grown from in‐country nurseries. Developers should therefore consider and build‐in the necessary lead times. Details to the contrary should be outlined and the reasons for sources elsewhere specified.

11.1.1 Landscape and Planting

General Guidelines

The landscape design must be carefully planned and take into account the intended purpose of the project and enhance the functionality of the community. Landscaping should reinforce design concepts and not obstruct or interfere with street signs, lights, or road/walkway visibility. The choice of species in all locations should be primarily indigenous and must meet and reflect local growing conditions with the size and scale of the tree appropriate to the location. Species should be chosen which require low maintenance.

Planting a. Provide planting at low levels to reinforce routes, mark focal points, and add to the visual

environment. Planting should be varied with a variety of colors and sizes of plants utilized. Species which flower at different times in the year should be used to ensure that spaces are attractive all year round.


b. In public squares, plant beds should be raised in order to reinforce routes, add visual interest, and prevent from being walked over.

c. Selection of plants should be based on climatic,

geological, and topographical conditions of the site. d. Annual color plantings should be used only in areas of

high visual impact close to where people can appreciate them. Otherwise, drip irrigated, perennial plantings should be the primary source of color.

e. Selection of water‐efficient and low‐maintenance plant material is recommended. f. All planted areas must be a minimum of 25 mm below adjacent

hardscapes to reduce runoff and overflow. g. Plants having similar water use shall be grouped together in

distinct hydrozones. h. Planter islands in parking lots with canopy trees to meet local

jurisdiction's shading requirements should have planter beds sized roughly by the expected canopy area in square meters equaling the square meter of planter bed.

Native desert plants shall be specified to be:

• Planted in a shallow, wide, rough hole three to five times the root ball width. • The root ball will be set on either undisturbed native soil or a firmed native soil. • The root ball top will be set even with surface grade or above grade if the soil is poorly drained. • The hole will be backfilled with native soil. • Extra soil may be brought in to mound up around plants where the soil is poorly drained. • Any organic material will be applied only as a surface mulch over the planting hole.

Grassy areas

a. Provide grass in all unpaved areas within parks and public spaces. The addition of grass in these areas will help prevent the spread of dust and sand. Grassy areas can also allow for picnicking and recreational activities.

Good use of raised beds to add interest to a public square and to prevent people walking on plants. Wall also serves as somewhere people can sit.

Use of colorful flowers to enhance the pathway and create an attraction.


Trees a. A cluster of trees should be established within landscaped areas,

providing a contrast to the built form or acting as a focal point. Trees will provide significant shading for all outdoor activities and should be located adjacent to pathways and hard paved areas. Tree pits and grates should be provided around all existing and newly planted trees in paved areas.

b. Use trees and bushes to provide wind screens and to visually separate car parking from the outdoor green space. In important areas designers may choose to use a more exotic selection of plants to emphasize the importance of the locations if designers can be confident that the resources exist to maintain these plants.

Turf Areas a. Large turf areas shall be found only in areas of maximum human contact. These areas include

recreational areas such as that found in city parks and school yards. Large, nonfunctional turf areas shall be minimized and reviewed to see if the same effect can be obtained with other plant material.

b. Avoid designing long, narrow or irregularly shaped turf areas because of the difficulty in irrigating uniformly without overspray onto hardscape and/or structures. Areas with less than 2.5 m in width and areas between sidewalks and curbs shall be planted to drip irrigated groundcovers and low‐growing shrubs. No turfgrass will be allowed in these areas unless subsurface drip irrigated.

c. The use of a soil covering mulch or a mineral groundcover of a minimum 50 mm depth to reduce soil surface evaporation is encouraged around trees, shrubs and on non‐irrigated areas.

d. The use of boulders and creek stones should be considered to reduce the total vegetation area; make sure these areas have enough shade to avoid reflected or retained heat.

e. Screening may be provided by walls, berms, or plantings.

f. Provide grass in all unpaved areas within parks and public spaces. The addition of grass in these areas will help prevent the spread of dust and sand. Grassy areas can also allow for picnicking and recreational activities.

11.1.2 Planting on Private Development Parcels a. Existing trees of calipers above 100 mm shall be encouraged to remain where use and grading

requirements allow.

b. All trees within residential and commercial parcels shall be nursery grown, container grown or ball and burlapped. All trees shall have a 75 mm to 100 mm caliper with 3.5 m to 4 m minimum height at time of planting. These trees shall grow to a minimum 125 mm to 150 mm caliper with a 5.5 m to 6 m height and shall be limb up (clear trunk) a minimum of 2.5 m above ground.

Example of tree grate in paved area.


Figure 11—1: Landscaping around the home (1)

Figure 11—2: Landscaping around the home (2)

c. There shall be at least one tree of the species listed, planted every 4.0 meters along project boundaries.

d. In parking areas, there shall be at least one tree of the species listed, planted for every 3

consecutive parking spaces (every 6 when they are back to back). The use of berms and additional trees along the perimeters of parking is encouraged to screen the parking area from public view.


e. All areas not occupied by buildings, pedestrian (sidewalk) or parking areas shall be landscaped. The use of native species of trees, shrubs, vines, groundcovers and perennials is required as standard.

f. Full maintenance and management regimes will be detailed for a minimum of five years. Use of native species will reduce these long term costs.

g. Shrubs of like species except those used as specimens shall be planted in‐groups rather than as

individuals. Shrubs shall be planted a minimum of 1.0 m on center unless otherwise indicated.

h. Planting clusters of fruit trees in groups of four or more (regularly spaced) is encouraged to create small orchards.

i. Areas for small herb and vegetable gardens are encouraged.

j. Hedges shall be a minimum height of 1.0 m with a spacing of 0.5 m on center.

k. Vines of listed species shall be planted along boundary walls and fences at a minimum of 2.0 m

on center intervals to insure continuous coverage and soften hard surfaces. One vine species shall be selected per boundary line.

l. Slopes greater than 3:1 shall be densely planted with masses of trees, shrubs, vines or

groundcovers in combinations of 9 or more of each, to achieve a lush effect.

m. The ground surface in rights‐of‐way and drainage easements is to be planted with grass species capable of tolerating the shade created by canopy trees. Grass may be seeded and mulched, or planted by plugs or sodded.

n. As a minimum requirement, each development parcel is to be provided with one canopy or

flowering tree for every apartment. In addition, a minimum of 20% of the yard area is to be planted in groundcovers or grasses. For single detached villas and units shall be provided with one (1) tree for every 150 square meter of building plot (lot area).

o. Planting areas are to be designed so that rainwater leaving the roof either long and edge or via a

gutter downspout, does not erode the planting. To this end drainage devices are to be installed in any area where concentrated water run‐off strikes the ground. Splash blocks of concrete, dry well, or connections to storm sewers are all acceptable means of preventing erosion on lots. Particular emphasis is placed on the need to cater for the dispersal and storage of storm water runoff.

p. Slopes and surroundings around retention ponds shall be landscaped with appropriate plant

materials. Basins of retention ponds shall be mown and kept free from rubbish (garbage) and regularly maintained.

11.1.3 Planting on Public Streets and Streets within Private Developments a. All trees in public streets shall be nursery grown, container grown or ball and burlapped. All

trees shall have a 75 mm to 100 mm caliper with 3.5 m to 4.0 m minimum height at time of


planting. These trees shall grow to a minimum 125 mm to 150 mm caliper with a 5.5 m to 6.0 m height and shall be limb up (clear trunk) a minimum of 2.5 m above ground.

b. All palms in public streets shall be nursery grown, container or ball and burlapped. All palms

shall have a minimum height of 6 m.

c. There shall be at least 1 tree of the species listed planted every 6.0 meters along both pedestrian pathways (sidewalks) of public streets, streets within private developments and public spaces.

d. In parking areas, there shall be at least one tree of the species listed planted for every 3

consecutive parking spaces (every 6 when are back to back). The use of berms and additional trees along the perimeters of parking is encouraged to screen the parking area from public view.

e. Trees and palms planted in rows or series shall be selected to insure uniformity of height,

caliper, and appearance between them.

f. Continuous hedges of one species shall be planted in front of parking spaces along each parcel frontage. Hedges shall be a minimum height of 1 meter planted at a spacing of 0.75 meters on center.

11.1.4 Planting on Public Parks and Landscaped Open Areas

Outdoor spaces are extremely important to any development. They are used as pedestrian routes and as places where people can relax and socialize. A large amount of resident’s time is spent outside and as such these spaces will have a very large impact on the quality of life of residents. Landscaping add visual interest to an area, makes pedestrian routes more enjoyable to use, and provide shading and wind protection to pedestrians where necessary.

This sub‐section covers parks, public squares, courtyards, and public gardens. Designers should make decisions based on strong concepts to ensure that the function of a space is clearly defined. Outdoor areas are most successful when they have a clear function and a unifying theme to aesthetic design decisions. Full information on design concepts should be submitted in accordance with specified requirements in Section 11.2 below. In addition to the criteria specifications outlined above, designs must comply with the following guidelines when delivering criteria:

a. On common landscaped open areas, provide common outdoor areas that are usable in all seasons, including shaded areas for outdoor use in warmer months.

b. Consider the special needs of each group of the expected residents. c. When located on ground level, open areas should be screened from public view by

landscaping, courtyard walls, or privacy fences.

d. On sloping sites, landscaped open areas should be sensitively terraced or provided in decks or balconies.


e. The requirements for private usable open areas could be reduced if a project provides some common usable open areas on the site.

f. Private open areas should be oriented to receive good sun penetration and provide

shaded areas for outdoor use in the warmest months.

g. Variety and Identity ‐ Designers must provide outdoor spaces which are interesting and add to the aesthetic environment. Outdoor space designs must be varied and should be an individual response to the area in which they are located. Outdoor spaces should be designed in conjunction with buildings to reinforce architectural themes and ideas.

11.2 Landscaping Plans Submittals Requirements The landscape design plan shall be drawn on project base sheets at a scale that accurately and clearly identifies the following specifications for Landscape Design: 1. Show tract name, tract number or parcel map number on cover sheet. 2. Show proposed planting areas. 3. Show plant material location and size. 4. Show plant botanical and common names. 5. Where applicable, plant spacing shall be identified. 6. Natural features including but not limited to rock outcroppings, existing trees and shrubs that

will remain incorporated into the new landscape. 7. Show a vicinity map showing site location on top sheet or on cover sheet. 8. Show a title block on each sheet with the name of the project, city, name, and address of the

professional design company with its signed professional stamp if applicable. 9. Reserve a 75 mm by 150 mm space for a district signature block on lower right corner of the

cover page and on all of the landscape, irrigation design/detail/specification sheets. 10. Show plan scale and north arrow on design sheets. 11. Show graphic scaling on all design sheets. 12. Show all property lines and street names. 13. Show all paved areas such as driveways, walkways, and streets. 14. Show all pools, ponds, lakes, fountains, water features, fences and retaining walls.


15. Show locations of all overhead and underground utilities. 16. Show total landscaped area in square meters. Separate area by hydrozone. Show the total

percentage area of each hydrozone. Include total area of all water features as separate hydrozones of still or moving water. Show Estimated Annual Applied Water Use, for each major plant group hydrozone and water feature hydrozone expressed in either seasonal (turfgrass) or annual (trees, shrubs, groundcovers, and water features) billing units.

17. Show Total Estimated Annual Applied Water Use for each major plant group hydrozone and

water feature hydrozone expressed in either seasonal (turfgrass) or annual (trees, shrubs, groundcovers and water features) billing units.

18. Show Total Estimated Annual Applied Water Use for the entire project. 19. Show Total Maximum Annual Applied Water Allowance for the proposed project. 20. Designate recreational areas and recreational turf areas. 21. When model homes are included, show the Maximum Annual Applied Water Allowance and

Estimated Annual Applied Water Use (by hydrozone with totals) for each model unit.

11.3 Landscape Grading Plan

1. The grading plan design shall indicate finished configurations and elevations of the landscaped areas, including the height of graded slopes, drainage patterns, pad elevations, and finish grade.

2. Turfgrass plantings are prohibited on slopes greater than three‐to‐one. Slopes steeper than

three‐to‐one shall be planted to permanent ground covering plants adequate for proper slope protection.

3. All grading must retain normal stormwater runoff and, as much as possible, provide for an

area of containment. All irrigation water must be retained within property lines and not allowed to flow into public streets or public rights‐of‐way. Where appropriate, a simulated dry creek bed may be used to convey storm drainage into retention areas. A drywell should be installed if the retention basin is to be used as a recreational area.

4. Avoid mounded or sloped planting areas that contribute to runoff onto hardscape. Sloped

planting areas above a hardscaped area shall be avoided unless there is a drainage swale at toe of slope to direct runoff away from hardscape. The swale areas may be planted to turf, ground cover, or low shrubbery and shall be watered separately.


Figure 11—3: Shrub and Tree Planting Details (1)

Figure 11—3: Shrub and Tree Planting Details (2)


Figure 11—4: Planting Details – Tree on Pavement

Figure 11—5: Hedge Planting Detail


Figure 11—6: Planting Details – Palm on Pavement

11.3.1 Tree and Plant Maintenance a. All landscaping should be provided with; (1) a planting regime plan; and (2) shall be accompanied with a

long term management and maintenance program. b. Trees shall be planted utilizing guy wires as shown in details to insure proper growth. All palm

trees shall be braced according to specifications. c. Plants shall be watered, mulched, weeded, pruned, sprayed, fertilized, cultivated, and otherwise

protected and maintained in a healthy condition. Irrigation of landscaped areas is required and these systems shall be maintained in working order.

d. Prior to establishment, settled plants shall be reset to proper grade position, planting saucer

restore, and dead material removed. Guys shall be tightened and repaired to restore tree to intended position.

e. Sod areas shall be mowed and edged regularly where they meet structures of pavement at bed

areas. f. Debris, including fallen branches, leaves, fronds, seedpods, and any foreign materials will be

removed from the site on a weekly basis. g. Hedges shall be pruned and maintained regularly to insure a uniform and continuous height of a

minimum of 50 mm and a maximum of 1.2 m above ground.


h. Pesticides shall be applied only in accordance to label instructions. Where possible environmentally‐friendly solutions to pest control should be applied. No pesticides shall be allowed to contact water surfaces.

i. All planting along public streets, streets within private developments and public spaces shall

have irrigation systems.

JUNE 2009 REVISION NO. 02 STREETSCAPE 12-1

12 Streetscape This section presents standard design criteria for streetscape. It has been developed for sources of best practice as a way of establishing a baseline, or minimum, for the standard of implementation sought in new developments.

Where appropriate proposals may be presented that provide additional detail, or standards. These will be considered on their merit, but must improve on the criteria herein and meet recognized international standards. Where alternatives are put forward and explanation must accompany the reasons why they are being proposed. In most, if not all instances, the use of appropriate qualified designers, engineers, technicians and other specialists is required as standard.

12.1 Introduction ‘Streets’ form the core of the transport network; Whether paved, with formal demarcation, as in many towns, or unpaved forming an informal thoroughfare through a rural settlement , streets are also the building blocks of the urban area, fulfilling a wide range of roles. They need to be managed to support all the objectives for any settlement however large or small. The functions of streets include: • Streets as movement corridors • Streets as the focus of activities • Streets as city identity All of these functions work together towards ‘place making’ and are influenced by the design of the street and the landscaping that contribute to the streetscape. A key component of ‘place making’ is the creation of public spaces, with footways that are sufficiently safe, attractive and comfortable to use so that people are encouraged to walk in the settlement they live for pleasure and function in a safe way. Footways should be sufficiently spacious for their purpose and be uncluttered. People see a scene in its totality. The space between buildings, usually the roadways and footways, is seen as part of a wider townscape made up of buildings and streets. Cherished views of important monuments and groups of buildings are appreciated far more when not detracted by unnecessary foreground clutter. Within this context there are opportunities for more exciting designs which have a place in the wider public realm and key spaces of the settlements in Libya. However, throughout Libya, it is essential that the design of streets should be clear and simple.

12.2 Good Design An essential element of a settlement’s visual character is the relationship between the buildings and the roadways and footways. There should be a presumption to maintain this relationship. Footways should be plain and simple, and generally uniform as a suitable setting for a settlement’s buildings. Traffic equipment and signs, together with their posts, supports, boxes and guard railings should be kept to the practical minimum. Roadway markings, applied colors, traffic lines and signs, etc. should


also be minimized while ensuring the aims of national transport standards of road safety. A street environment must also welcome pedestrians. The objectives of creating a public realm of real quality, with road safety issues central, can be achieved by attention to design detail. While it is not always possible to undertake comprehensive public realm improvements, in the same way that a series of poor changes can result in a degradation of the public realm so positive changes can, over a period of time, help to regain the standards of public realm quality that Libyan cities deserve. This embraces the following practices: • Roadways – how curbs/edging, footpaths and drainage channels are laid out, mounting stones and

lighting plinths set and to what standards and specifications.

• Footpaths – securing the key elements of a footway ‐ curb, drainage, channel and roadway. Considering how slabs are aligned, odd sizes cut (on the inside of the footway and shaped to the profile of the building or boundary), sizing and quality specifications.

• Features – monitoring and regulating the numerous additional features that have appeared as part of the street scene. These include spur stones, bollards, railings and gateposts.

• Street relationship ‐ The critical relationship between the roadway, pavement width and alignment and the building property boundaries. The growth in car ownership has led, often forced, the adaptation of our streets for a variety of reasons, including accommodating increased levels of traffic. Retaining and reinforcing these relationships is a key objective. This does not mean that curb lines cannot change. However, the manner in which the changes are made must maintain the relationship.

• Street pattern – New streets are being created all across Libya. It is important that these new streets and new public spaces use a design language that is derived from existing streets and spaces, providing positive connections back to existing parts of a settlement or area. It is also important that these new development areas utilize a recognizable range and ‘palette’ of materials.

12.3 Overarching Objective The guidelines have been developed to help redefine those elements of street design that make up its character and to ensure new proposals that impact the streetscape are designed, as far as practicable, to improve and at the very least reinforce the existing character. An over reaching objective is therefore:

… to facilitate the delivery of a streetscape that provides an enhanced environment for pedestrians that is designed to respond to its built context and, at the same time,

meets the requirements of traffic movement… .

12.4 Principles The following ‘eight‐principle’ approach is advocated for adoption: Principle 1 – Preservation and enhancement of settlements historic form and ‘grain’, particularly in


locations with a high heritage and archaeological value (e.g. world heritage status medina), both during and after construction phases. Principle 2 – For renovation and rehabilitation areas, respecting and enhancing local character. Ensure that when new street works are proposed they take the local character of the area as a reference point for the design of layout and overall design arrangement and detailing. Principle 3 – New streets to contribute to formation of recognizable street pattern. They should be designed as part of a recognizable ‘townscape’ that picks up on street characteristics specific to the settlement. They should form a part of a coherent relationship between building, footway, roads and other features. Principle 4 – Contributing to Place Making, creating streets that people would wish to use. Streets are the arena where the public interface takes place and, as such, should be designed so that they are not dominated by traffic or with over complicated instruction and segregation. Instead they should reflect human scale and be simply designed in a manner that is easily understood and attractive to pedestrians.

Principle 5 – Best Practice. If there is a real desire to create streets that people wish to use, it will be necessary to draw upon and experiment with international best practice. For example, consider a reduction in traffic related signage and markings without putting people at risk. Principle 6 – Achieving Quality of the public realm can be achieved through the careful consideration of a number of measures. Taken together these will have a significant impact on the appearance of the streets. These include a

reduction in clutter, using natural materials, drawing on a minimum number palette of materials, simple, clean designs and a coordination of design and color. Principle 7 – Maintenance. A well‐cared for public realm is the result of good design and effective on‐going maintenance. The type of simple clean design to which a settlement should aspire would make maintenance easier. Maintaining and managing an uncluttered, simple street design requires all those involved in the public realm to share in a philosophy of care. Principle 8 – A Coordinated Approach across a settlement will only be achieved if the appropriate processes and protocols are in place. Adherence to these is the key to consistency and ensuring that high standards of design are maintained through the life of any scheme.


12.5 Design Guidelines and Criteria

12.5.1 Planting Regimes

Planting regimes, on‐street trees and landscaping provide an attractive and healthier urban environment‐ contributing to a sense of place and improving air quality and linkages in habitat networks. Correctly positioned, street trees can provide an important contribution to the urban structure of any settlement or city, providing accents and space in contact with the urban built form, with many public squares or meeting places enjoying the setting of significant trees.

In the ‘suburban’ development areas trees are focused on gardens, where they complement the streetscape, predominantly from behind a boundary walls. New development offers the opportunity to increase tree cover and general landscaping. In any development trees should be used to reflect varying approaches, introduce ‘color’ and ‘texture’ into the development. The following guidelines should be considered:

• Trees should be planted into designated soft landscaped areas where possible, in preference to hard surfaces.

• In general public street arrangements/through streets, etc, preference will be for trees to be located within gardens and frontages, where appropriate and not in the footway.

• Groups of trees should be established within landscaped areas, providing a contrast to the built form in a street layout, acting as a focal point to a view and providing shade.

• Where existing trees are to be retained, the general arrangement of the street and public realm should be designed to take account of the trees requirements.

• Consideration should be given to the impact of underground services on proposals.

• Tree grids should be porous resin bonded gravel or a more solid concrete/metal cover flush with the surrounding paving (unless an ‘up stand’ is more suitable).

• Tree guards should not be used.

• Generally trees in paving should be planted to a minimum of an extra ‐heavy standard size (to ensure they have a proper chance of surviving and prospering)

• Street trees planted into landscaped areas should be standard or smaller size.

• The choice of species in all locations must meet and reflect local growing conditions and the size and scale of the tree appropriate. Wherever possible they should be locally sourced and grown.

Clearly planting regimes will differ greatly across Libya, based on their geography (coastal, desert or mountain) and location (city or rural area). It is proposed that individual fact sheets on preferred planting schemes, making recommendations on the type, size and age of species, should be prepared by the relevant specialists in due course.


Planting regimes should also have a wider reference to supporting wildlife. Where appropriate plants should be selected that increase the instances of attracting and supporting the local fauna.

12.5.2 Footway layout

Footway layouts should be designed for the use and enjoyment of pedestrians. They should provide sufficient space for the user, provide a setting to the adjoining buildings and be as clear and clutter free as possible. The layout of footways should be simple. Public footways should not be used to take up differences in level when new entrances to buildings are being created.

• Respect the proportional relationship between the footway, buildings and the roadway (with a presumption against reducing footway widths).

• Ensure footways avoid awkward or abrupt changes in level and access or frontages with developments are clear and uninterrupted.

• Vehicle run‐ins and crossovers (for access to buildings and parking for example) should not normally interrupt the footway layout. Dropped curbs and reinforced surfaces are recommended.

• Retain existing access where it would provide reference to the character of the area.

• Protect, strengthen or increase heights of curbs where appropriate in new schemes or high use areas where extensive maintenance proposals may be required.

• Materials should be consistent to make maintenance and replacement easier.

12.5.3 Paving

Paved pathways should be provided from the car parking to the entrance of the building. Provide paved areas for pedestrian pathways, seating areas, child play areas, and other features. Provide adequate dedicated bicycle lanes throughout the development.

Paving should be modular, a minimum of 500mm x 500mm and be constructed from stone, precast concrete or grass‐crete. A variety of paving types should be used throughout the development to add identity to different areas.

Paving is an integral part of the footway streetscape. Some simple applications should be promoted. For example:

• Small module paving (below say 450mm by 600mm) should be avoided for footways, preferring larger unit paving or simple flexible surface treatments. (500mm by 500mm should be the smallest unit used).

• Use precast concrete, grass‐crete or asphalt.

• Include the use of colored tactile (blister and hazard) paving at crossings and hazards as a warning at steps. The resulting contrast provides the necessary signal for those who are visually impaired. Consider the need of specific users who may live in or near the area, such as the elderly or visually impaired.

In areas outside or adjoining the public street, such as squares and public spaces, there are opportunities to


introduce a wider variety of materials and paving styles that respond to modern design proposals. However these should relate clearly to adjoining street footway paved areas in their general arrangement and there will be a presumption for the use of natural paving materials in key public spaces.

Roadway curb lines and in most streets curb ‘up stands’ are an essential part of the design and layout of the street.

• Curb lines should be used at all times to define a footway and should run parallel with the building line.

• Newly laid curb ‘up‐stands’ shall normally be set to a minimum of 125mm. In many urban settlements across Libya, consider higher up‐stands to prevent parking and provide a suitable alternative to bollards to protect the footway.

Pedestrian crossings and associated refuge islands should be designed as complete entities and to consistent details. Designs should seek to introduce the minimum requirements to avoid unnecessary clutter (e.g. guard rails should be avoided) and should ensure that the surrounding footway and roadway designs are consistent in detail, material and proportion to their surroundings.

The scale and proportion of the roadway means that it can have a marked impact on the appearance of the street. The choice of materials and infrastructure used affect this appearance.

The maintenance of the roadway is important and an excessive use of different materials and features can be a burden to upkeep. Simplifying the design and layout of these features and thinking about the requirements in a particular location rather than just applying the standard can help ease such a burden. Materials should therefore be consistent to make replacement and maintenance easier.

Awareness of emerging best practice for standardized solutions should also be considered at the start of the project where there is scope for improving the overall design of proposals. This recognizes design philosophies are changing and new approaches are being tried. It is essential that safety is maintained in the design and application of any approach at all times.

Roadway, parking and loading restriction lines and markings ‐ should be applied (in the narrow 50mm wide format), replacing original lines and with careful consideration to how they are applied to local features.

Raise entry treatments and speed tables enhance conditions for pedestrians on busy footways. Entry treatments are a common way to persuade drivers to give way to pedestrians. ‘Movement and Development’ requires that raised crossings, as far as possible, send a visual message to motorists and pedestrians that the footway continues across the side street. The area of raised roadway should have a tactile surface at its footway edge at the crossing point. They should be tall enough to discourage unauthorized access without restriction visibility lines.


At junctions and at crossing points in the street, the curb should be dropped to improve crossing facilities. The dropped curb should be on the direct pedestrian ‘desire’ line, so that pedestrians are able to cross the road conveniently and preferably at right angles to the direction of pedestrian travel. A minimum width of 3 meters should be specified, dependant on site conditions. Exceptional numbers of pedestrians, in locations normally within Libya’s larger cities, may require the

width to be increased to 10 meters.

12.5.4 Street Furniture and Features

Street Furniture and Features are often provided in the context of the street in addition to signage. These features also have an effect on the setting of the surrounding urban form as well as the overall function of the street. All street furniture and features should be located with this in mind. The presumption will be to co‐ordinate and in some cases minimize furniture and features, taking into account the requirements for signage outlined above.

• Sitting is an important aspect of ensuring unobstructed footways. A desired minimum of 1200mm unobstructed footway is required which will generally extend from the building line towards the front of the footway.

• The use of guardrails and bollards to protect vehicle overrun should be limited.

• Simple contemporary standard furniture and features will be used consistently in general street arrangements.

• Key or unique public spaces (such as new squares, local shopping centers, look‐outs or waterfront locations) could be considered for alternative solutions (feature sites).

Whilst the styles and designs of many items of street furniture will be standardized, there are, however, opportunities to introduce elements of public art to add interest or texture to streets and spaces. This can range from the use of carved stone and metalwork features to the location of major pieces of public art. Opportunities for public art will best be highlighted through development briefs and master plans. Any art proposed will consider the maintenance implications, resources for upkeep and local characteristics.

12.5.5 Lighting Provide and install lighting to illuminate pathways, seating areas, playgrounds, landscaping, important features and buildings. Lighting is important for security and safety and allows people to use outdoor spaces after sunset.

Lighting detailing, style and the type of light source should be considered with consistency, long term maintenance as key considerations. Positioning should be considered in the context of the street scene.


The choice of light source is important as it will determine the night time appearance of the area in which new lighting is installed as will the position of the lighting units in order to achieve the required lighting standard.

Consideration and adaptation to best practice is vital. The current lamp sources being specified are mainly high pressure sodium (SON), metal halide and compact fluorescent (CDM, PL). There is an ever increasing range of lamp sources and only the most efficient available should be used wherever possible to help reduce future maintenance and energy costs.

Specific detailing can be provided for additional street features, including bollards, railings and gateposts, traffic lights, CCTV cameras, seating, tables and chairs,

trade, domestic and recycling bins, control, power and telecom panels.

12.5.6 Benches Designers should provide benches for outdoor seating in the green space and near the buildings. Locate benches in shaded places. Benches can be placed individually to create private spaces for individuals or in groupings to create a public place. Benches should be very durable and attached to paving or otherwise anchored. At any point within an open space people should not have to walk far to get to somewhere where they can sit down. Benches should be incorporated into the overriding themes of patterns. A variety of materials, textures and lightings can be used to provide variety in the types of benches provided. Benches should be made from very durable weather resistant materials and should be designed to require as little maintenance as possible.

12.5.7 Planters In public squares raised beds should be used in areas to bring plantings closer to eye levels and to stop people from walking on the plants and flowers. Provide planting beds filled with plants sensitive to the local environment. The form of planting should create a layering of textures, colors and plant forms, creating geometric pattern and texture derived from Islamic culture.

12.5.8 Playground Equipment Provide playground equipment in the outdoor spaces for each cluster of buildings in line with national and international guidance. Playgrounds should be located in an open, visible area which can be seen from building windows for


supervision. They must provide an appropriate ground surface to prevent injuries. Use only high quality equipment which can be easily maintained and has appropriate international safety specifications. Fence off play areas providing a single access point to increase security and to enable parents to monitor children more easily. Provide benches for parents to rest on while children are playing.

12.5.9 Water Features in Public Open Spaces Water features should be used in significant public spaces to provide focal points and landmarks. In hot climates providing cooling fountains which children can play in may be popular. Only water features which use water sparingly and reuse water should be used due to the scarcity of water in Libya. Consideration should be given to what maintenance a water feature will require and only fountains with commonly available parts should be chosen.

12.5.10 Shading Strategies Shade structures may incorporate lighting, ventilation fans, misting, plants, retail signage and seating. Canopies and trellises can also be used in a variety of ways to provide shade and reduce heat affects. They will be used for public gathering locations as well as playgrounds. Canopies and trellises should be made of heat reflective materials (e.g. light wood, tensile fabric, metal, etc.) Shading structures should varied be used to reinforce themes within areas. Provide at least one pavilion or shading structure for each cluster of buildings constructed using durable, permanent materials. Use trees to provide shade to important pathways.

12.5.11 Signage The street with its footways and roadways form the setting to the surrounding buildings and urban form. All signage should be located with this in mind, adopting national standard specifications at all times. The presumption will be to minimize signage. This can be achieved in some cases through consideration of alternative locations as well as combined use and operation.

In general signage should be considered on a street/site specific basis, but proposing a consistent approach for the entire street or area where possible and should consider the following approach. This should embrace:

• Locate signage onto buildings, walls and street furniture, where possible and reduce the

use of poles to minimize clutter.

• Poles for signs will be positioned to the rear of the footway or 450mm from the curb edge in both cases ensuring that the middle of a footway is not obstructed.

12.6 Delivering the Principles

A structured program of steps to aid in the delivery of these principles is advocated. This will ensure the broad principles are applied sustainably and reflect local characteristics and conditions whilst maintaining good design practice. The objectives of sustainability, low maintenance and long term enjoyment will drive this implementation process and in so doing encourage wider training and development for the adoption of best practice methods and simple solutions.

JUNE 2009 REVISION NO. 02 BRIDGE Inspection 13‐1

13 Bridge Inspection

13.1 Introduction

This provides guidance for bridge inspection personnel, provides a reference for consultants, and helps to ensure consistency in bridge inspection, rating, and evaluation. This section contains: Introduction; Qualifications, Responsibilities, and Duties of Bridge Inspection Personnel; Field Inspection Requirements; Ratings and Load Posting; Routing and Permits; Bridge Programming; Bridge Records and an Appendix.

13.1.1 References The publications related to bridge inspection with their issue dates are:

1. AASHTO Movable Bridge Inspection, Evaluation, and Maintenance Manual, 1st Edition , 1998 2. AASHTO Manual for Bridge Evaluation, 1st Edition, 2008 3. FHWA Bridge Inspector's Reference Manual, 1st Edition (December 2006) 4. NCHRP Maintenance and Inspection of Fracture Critical Bridges, 2005

5. AASHTO Manual for Maintenance Inspection of Bridges (1993) 6. AASHTO Manual for Condition Evaluation of Bridges (1994) 7. AASHTO Guide Specifications for Fracture Critical Non‐redundant Steel Bridge Members, 1986 8. AASHTO Interim Specifications for Bridges, 1990 9. AASHTO Standard Specifications for Highway Bridges, 17th Edition 2002 10. AASHTO Guide for Selecting, Locating, and Designing Traffic Barriers , 1977 11. AASHTO Load and Resistance Factor Design Specifications,2004 12. ASTM Standard Terminology Relating to Fatigue and Fracture Testing, ASTM 1823‐96e1 13. ASTM Specification for Carbon Structural Steel A36/A36M ‐97 Volume 01.04, 1997. 14. FHWA National Bridge Inspection Standards (1988) 15. FHWA Recording and Coding Guide for the Structure Inventory and Appraisal of the Nation’s

Bridges (1972, 1979, 1988, 1991, and 1995) 16. FHWA The Bridge Inspector’s Manual for Movable Bridges (1977) 17. FHWA Culvert Inspection Manual (about 1979) 18. FHWA Inspection of Fracture Critical Bridge Members (1986) 19. FHWA Scour at Bridges, a technical advisory (1988) 20. FHWA Hydraulic Engineering Circular No. 18 (about 1988) 21. FHWA Bridge Inspector’s Training Manual 90 (1991) 22. FHWA Scour at Bridges, Technical Advisory, 1988 23. TxDOT Administrative Circular No. 60‐75,1975TxDOT Construction Specifications, 1962 24. TxDOT Memo from C.W.Heald,P.E. Closing of Weak Bridges, February 1999 25. TxDOT Memo from Robert L. Wilson, P.E Texas Transportation Code, Title 7, Chapter 621 Closing

and Posting Recommendations for Off‐System Structures, October 1997 26. NHI (National Highway Institute) Safety Inspection of In‐Service Bridges 27. Texas Bridge Load Rating Program of 1988 28. National Society of Professional Engineer’s program for National Certification in Engineering


Technologies, National Institute for Certification in Engineering Technologies (NICET) 29. Traffic Management Section, HIB Design Criteria .

13.1.2 AASHTO Inspection Manuals 1974 AASHTO Manual (The small “green book”) described the minimum information considered necessary for inspection, records, rating, and check of bridge load capacities. Primary subjects with their major items were: Inspections

• Frequency of two years

• Waterway, debris, and channel profile to be observed

• Investigate evidence of scour and undercutting

• Deterioration of main structural members, deck, superstructure, and bents

• Fatigue details of steel girders to be considered (little guidance given)

• Abnormal cracking in concrete members

• Bridge railings to have only visual inspection, no strength requirements

• Trusses inspected for damage, bracing, condition of paint Records

• Written Structural Inventory and Appraisal (SI&A) sheet

• Condition Ratings given as 9 to 0 as now, but little guidance on selection of ratings

• At least two photos to be taken

• All normal identifications, widths, clearances, etc. to be recorded

• Painting record to be kept

• Stress calculations to be kept

• All spans should be listed by length. Ratings

• Calculations in accordance with current AASHTO bridge specifications


• Operating and Inventory Ratings to be H‐ or HS‐equivalents

• Higher safety factor allowed for heavily traveled routes

• Dimensions from as‐built or field measurements if necessary

• Pictorial posting signs recommended.

Load Capacity of Bridges

• Consider two lanes loaded with rating trucks if bridge is 5.50 M clear or wider

• Allow fewer lanes if warranted by judgment of Engineer

• “Train” of lighter‐weight trucks to be considered, spaced at 9.10 M headway when at H12 or less

• Load distribution and allowable stresses as given by AASHTO Bridge Specifications

• Sample calculations given in Appendix B of AASHTO Manual

• Load Factor Rating introduced as an acceptable method 1978 AASHTO Manual The third AASHTO Manual was issued in 1978 (the small “yellow book”) and included all the same information and requirements as the first two AASHTO Manuals, with some reordering of contents. In addition, the following major additions and modifications were made as compared to the 1974 AASHTO Manual: Records Recommendations modified for repair, maintenance, and posting Ratings

• Definition of Inventory Rating changed to omit the equivalency to the original design load

• Typical load and speed posting signs omitted and reference made to Traffic Management Section, HIB Design Criteria.

Load Capacity of Bridges

• The “Secant Formula” was added for steel column strength calculations (this formula is believed to be out‐of‐date and should not be used by a rater)


• Allowable Inventory Rating stresses listed for A36, A572, A441, and other steel types

• Increased allowable bearing stresses on rivets and bolts 1983 AASHTO Manual The 4th AASHTO Manual was issued in 1983 in loose‐leaf form (the large “yellow book”) and contained essentially the same requirements as the first three AASHTO Manuals. The Records and Ratings requirements were essentially unchanged from the 1978 AASHTO Manual. The following list summarizes the major additions and modifications since the 1978 AASHTO Manual: Load Capacity of Bridges

• Allowable Inventory of Rating stresses became more detailed

• Allowable bearing stresses on rivets and bolts for Operating Ratings was again increased to be consistent with the increases made in 1974 for Inventory Rating

• Allowable Inventory stresses for A7 bolts and rivets clarified

• Allowable Operating Rating stresses for high‐strength bolts detailed for all conditions

• Comparative chart for fastener bearing stresses added

• Maximum Operating Rating concrete stresses in bending clarified

AASHTO Interim Specifications The AASHTO Interim Specifications of 1984 through 1990 included some re‐ordering and editing of various sections of the 1983 AASHTO Manual. In addition, there were significant changes and additions made in certain sections. These changes are summarized as follows:

• In 1984 the inspection frequency could be increased to more than two years for certain types of bridges if properly documented. An example is reinforced concrete box culverts.

• In 1984 the two lanes of live loading for roadways between 5.5 M to 6.0 M was clarified. For

roadways over 6.0 M in width, the spacing between trucks became 1.20 M, which is the same as the AASHTO bridge specifications. This corrected a long‐time disparity between the bridge specifications and the AASHTO Manual.

• In 1986 there was a major change in the qualification of inspection personnel which required

that the individual in charge must be a Registered Professional Engineer. Prior to this time, the individual in charge could be qualified by experience.

• In 1986 scour was specifically identified as an item requiring more intense inspection.

• In 1986 non‐redundant structures were identified as requiring the initiation of special inspection


procedures.

• In 1986 concrete bridges with no plans were allowed to be rated by simple physical inspection and evaluation by a qualified engineer.

• In 1987 underwater inspection was identified as an important inspection requirement.

• In 1987 hangers and pins were identified as features to be properly inspected.

• In 1987 new sections entitled Evaluation and Limiting Vehicle Weights were added. Higher

safety factors could be considered for structures with large volumes of traffic. In addition, the agency responsible for maintenance of a structure could use stress levels higher than Inventory Ratings to post a bridge if inspection levels exceeded the minimum.

• In 1987 speed postings were allowed in certain cases to reduce impact loads and thus reduce

the need for lowering weight limits.

• In 1988 the requirement that all inspections be done by a Registered Professional Engineer was re‐interpreted to allow an inspection team leader to be qualified by experience. However, the person in responsible charge must be an Engineer.

• In 1988 emphasis was placed on underwater inspection of pilings, particularly those exposed to

salt water or salt spray, and any foundation member in contact with brackish or chemically contaminated waters.

• In 1989 the minimum weight limit for posting was clarified to be three tons at the Operating

Rating stress level.

• In 1989 a new Appendix B was added that described the five basic Inspection Types:

Inventory

Routine

Damage

In‐Depth

Interim • The categories and description of each Inspection Type were relatively broad. However,

clarifications were made that the first Inventory Inspection was to determine all the Structure Inventory and Appraisal data required by FHWA and that Routine Inspections were defined as those done at regularly scheduled intervals.

• In 1990 only minor editorial changes were made.


AASHTO Manual, 2000 AASHTO adopted the 2nd Edition (148 pages, loose‐leaf) Manual for Condition Evaluation of Bridges and is considered current at this time June 2009. Major additions and changes since the 1983 AASHTO Manual are: Records

• Total bridge width is to be recorded. Prior to this time, the total was implied by the summation of the deck width, sidewalk or curb width, and railing type.

• Critical features such as special details, scour susceptibility, fatigue‐prone details, etc. are now

to be recorded.

• Flood records are to be kept if known. This information is not entered in the Coding guide, but should be kept in the Bridge Folder described in Subsection 13.7.

Inspections

• Qualifications of the Inspection Program Manager are changed again to allow the person to be qualified by experience. Qualifications for Inspection Team Leader are modified to allow training to be based on a National Institute for Certification in Engineering Technologies (NICET) Level III or IV certification in Bridge Safety Inspection.

The five basic Inspection Types are now called:

• Initial

• Routine

• Damage

• In‐Depth

• Special The categories and description of each Inspection Type are essentially the same as described for the 1983 AASHTO Manual as modified by the 1989 Interim.

• Detailed sections are added on methods of inspection including equipment, safety, advance planning, and preparation for inspections.

• Sections are added to describe inspection procedures, including organized and systematic field

notes and procedures.

• Emphasis is placed on obtaining uniformity in condition ratings by different field inspection


teams by developing an objective system of evaluation and training.

• New emphasis is placed on inspection of substructures including susceptibility to earthquake damage.

• More emphasis is placed on various types of substructure inspection.

• Detailed inspection recommendations are given for each of the various types of bridge

superstructure including new superstructure types such as cable‐stayed and pre‐stressed concrete segmental bridges and new component types such as pre‐stressed deck panels.

• Fracture‐critical members are to be properly identified.

• More detail is required on description of timber components.

• Greater detail is added on inspection of trusses.

Material Testing

• Extensive new material is added on field testing of materials for concrete, steel, and timber including reference to the various newer methods such as acoustic emission for steel and pull‐off and thermographic tests for concrete.

• Sampling techniques are described in detail.

• Interpretation and evaluation of field and laboratory material tests is discussed.

Non‐Destructive Load Testing

• This is a new section in the AASHTO Manual. However, very little useful information on actual load testing procedures is given.

• Methods of determining equivalent standard ratings from load tests are complex and costly, and

are seldom used. Ratings

• The rating section of the AASHTO Manual is much more extensive than corresponding sections in previous editions.

• The description of the safety factors for the Load Factor Rating method is similar to the factors

in the new AASHTO Load and Resistance Factor Design (LRFD) Specification.

• The AASHTO Manual now states when a redundant bridge has details not available from plans, then a physical inspection and evaluation may be sufficient to approximate the ratings. An interpretation on applying this criterion to redundant bridges will be presented in Chapter 5, Ratings and Load Posting.


• Structural grade of reinforcing steel is listed separately in the Load Factor Method of rating but

is combined with all the older unknown grades for the Allowable Stress Rating Methods. • The AASHTO Manual now contains detailed examples of allowable stress, load factor, and load

and resistance factor (LRFR) ratings for a simple‐span, I‐beam structure and for a simple‐span, concrete structure.

13.1.3 Inspection Procedures The FHWA Bridge Inspector’s Training Manual 90 was published in July 1991 and is the basic current reference for all field inspectors. Hereinafter it will be referred to as Manual 90. Manual 90 presents the basic information needed by all bridge inspectors and rating personnel. It includes an excellent history of the National Bridge Inspection Program. It also includes a description of all the common types of bridges, materials, and details used in bridge construction. Recommended procedures are presented in detail along with many diagrams and photos. Manual 90 also presents a fair description of basic structural mechanics for bridge members. The purposes of bridge inspection are:

• Primarily for preventive maintenance

• To ensure public safety and confidence in bridge structural capacity

• To protect public investment and allow efficient allocation of resources

• To effectively schedule maintenance and rehabilitation operations

• To provide a basis for repair, replacement, or other improvements such as retrofit railings Bridges are inspected every two years, but the frequency may be increased depending on the condition of the bridge. More detail will be given in Chapter 4, Field Inspection Requirements. There are five basic types of inspection, each of which will be described in greater detail in Chapter 4, Field Inspection Requirements:

• Initial Inspection. Performed on new bridges or when bridge is first recorded.

• Routine Inspections. Those regularly scheduled, usually every two years for most normal bridges

• Damage Inspections. Those performed as a result of collision, fire, flood, significant environmental changes, loss of support, etc. These inspections are also called Emergency Inspections and are performed on an as‐needed basis.

• In‐Depth Inspections. Performed usually as a follow‐up inspection to better identify deficiencies

found in any of the above three types of inspection. Detailed Underwater Inspections are considered a type of In‐Depth Inspection. Fracture‐critical Inspections are another type of In‐


Depth Inspection.

• Special Inspections. Performed to monitor a particular deficiency or changing condition. Unusual bridge designs or features such as external, grouted, post‐tensioned tendons may require a Special Inspection.

13.2 Qualifications, Responsibilities, and Duties of Bridge Inspection Personnel

13.2.1 Requirements General Requirements Personnel involved in the various bridge inspection activities must be qualified for their specialized jobs. In general, depending on the level of responsibility, they must be knowledgeable in the various aspects of bridge engineering including design, load rating, construction, rehabilitation, and maintenance. HIB Requirements These are summarized as:

• The individual in charge of the Bridge Inspection of the RBD, or the contract consultant firm) must:

• be a Licensed Professional Engineer, or

• be qualified for licensing, or

• have a minimum of ten years experience in bridge inspection assignments and have completed a

comprehensive training course based on the Bridge Inspector’s Training Manual 90.

• The individual in charge of a bridge inspection team must:

have the same qualifications as above, or

have a minimum of five years experience in bridge inspection assignments and have completed a comprehensive training course based on the Bridge Inspector’s Training Manual 90.

AASHTO Requirements These are described in the current AASHTO Manual for Condition Evaluation of Bridges.


HIB Requirements At a minimum, all bridge inspection activities performed by Contractors must comply with HIB requirements. HIB requirements for bridge inspection personnel are also the same as those in AASHTO requirements, and in addition, some jobs may require more specific job‐related knowledge and skills such as:

• The use of breathing apparatus for underwater inspection

• The various applicable requirements for inspection safety including applicable Occupational, Safety, and Health Administration (OSHA) requirements

• Advanced computer skills related to bridge analysis

• Geotechnical and hydrological knowledge

• Familiarity with HIB bridge construction specifications and with current and old HIB bridge

designs HIB also has special requirements for Contractors retained to perform bridge inspection tasks. All firms must be pre‐qualified. Further information on Contractor requirements is presented later in this chapter in the section titled “Bridge Inspection by Contractor”.

13.2.2 Bridge Inspection Personnel General Position Requirements Certain knowledge, skills, or abilities are general in nature to most bridge inspection engineering‐related positions. The level of knowledge, skill, or ability in these general areas increases in relationship to the level of the position and will not be specifically described for each of the positions. Some of the particular areas of necessary skill and knowledge for bridge inspection personnel are:

• Ability to perform engineering calculations

• Knowledge of bridge engineering fundamentals and application of engineering theory

• Ability to analyze, interpret, and review technical data

• Ability to use a personal computer along with applicable software

• Knowledge of all types of bridge construction methods in North Africa and the Gulf Region

• Knowledge of AASHTO specifications, HIB design procedures, bridge standards, and details

• Ability to exercise initiative and independent engineering judgment

• Ability to schedule and lead the work of others when appropriate to the position


• Ability to communicate effectively and maintain proper working relationships

Various special skills and knowledge are also necessary for some of the positions, some of which are unique to the bridge inspection operations such as:

• Knowledge of applicable local laws and regulations

• Knowledge of bridge inspection methods and procedures

• Familiarity with associated inspection safety requirements

• Skill in use of scuba or other underwater inspection equipment

• Ability to make bridge inspection‐related technical and training presentations and to represent the department in public meetings and conferences

13.2.3 Bridge Inspections by Contractors General Requirements All firms contracted by HIB to perform routine bridge inspections must be pre‐certified in accordance with the requirements of all applicable codes. All bridge inspections shall also be performed in accordance with this Manual.

Routine Bridge Inspections For routine bridge inspections, the firm must employ an individual to serve as Project Manager who meets the following qualifications.

• Is a Licensed Professional Engineer, or

• Has a minimum of ten years experience in bridge inspection assignments in a responsible capacity.

The bridge inspection Team Leaders employed by the firm must also be qualified and have:

• The same qualifications as above for the Project Manager, or

• Has a minimum of five years experience in bridge inspection assignments Complex Bridge Inspections For complex bridge inspections, such as those requiring fracture‐critical inspections, the firm must employ a minimum of one Licensed Professional Engineer, to serve as Project Manager, who has seven (7) years of bridge inspection or design experience, including one year of inspection or design of bridges considered as complex


The firm must also employ as a complex bridge inspection Team Leader, an individual who has a minimum of six years of bridge inspection or design experience, including one year of inspection or design of bridges considered as complex. Precertification Procedures for Contractors Bridge inspection contracts are developed and monitored by RBD personnel. Contractors must be able to demonstrate the required minimum amount of experience in bridge inspection, rating, and evaluation. Consultant personnel must have completed the required training in bridge inspection. Familiarity with HIB Master Specifications is necessary. Strong knowledge of HIB Bridge Construction Specifications and Bridge Design is also necessary.

13.2.4 Use of the Contractor Pool Contractor firms who are pre‐certified to perform bridge inspections are to be made available to HIB. The list of certified firms is updated by the RBD every two years. The necessary procedures that must be followed to utilize these Contractors is described below. Request for Contractor Inspection The RBD with a lead time of at least two to three months shall initiate the following ; A request in writing An estimate of the total numbers of bridges to be inspected An identification of the bridges as being on‐ and/ or off‐system and shall forward to RBD Head for approval citing reasons why Contractors are to be engaged; Work Authorization Issuance The RBD will send the Contractor a Work Authorization along with a fee schedule. The work authorization shall include the following;

• Description of where the bridge inspections will take place

• Number of bridges to be inspected by type

• Total Libyan Dinar amount on the Work Authorization

• Termination date for the completion of the inspections


Once the work authorization has been accepted by the Contractor, they may begin bridge inspections. Managing the Contractor Bridge Inspection To ensure that bridge inspections are being performed in a competent and timely fashion, the RBD will perform continuing oversight of the work by following these steps:

• Verify the Contractor’s bridge inspection Project Engineer and the individual Team Leaders against the list provided by the RBD.

• Periodically visit the Contractor’s inspection teams in the field to verify team composition and to observe actual inspections

• When completed inspections are submitted by the Contractor, the RBD should review at least

10 percent of the office work and 7 percent of the field work

• RBD should monitor the amount of completed Contractor bridge inspections to ensure that additional structures that might be added as the work progresses will be noted and adjusted in the Work Authorization

• If additional funds or time is needed to complete the Work Authorization, a request for a

Supplemental Agreement must be made to the RBD.

• A Supplemental Agreement request should be made to the RBD at least 2 weeks before the termination of the initial Work Authorization

Completion of Work Authorization When the bridge inspections covered by the Work Authorization are finished, The RBD should complete an HIB evaluation form.. This aids in ensuring the overall quality of the work provided by the Contractor, and also aids in the Contractor pool selection for the next two‐year cycle.

13.3 Field Inspection Requirements

13.3.1 Types of Bridge Inspection

There are five basic types of bridge inspection:

• Initial Inspections

• Routine Inspections

• Damage Inspections

• In‐Depth Inspections


Underwater Inspections and Fracture‐Critical Inspections are two types of In‐Depth

Inspection

• Special Inspections

Inspection of post‐tensioned, grouted, external tendons is an example of a Special Inspection.

13.3.2 Initial Inspections Initial Inspections are performed on new bridges or when existing bridges are first entered into the database. This inspection provides a basis for all future inspections or modifications to the bridge. Initial deficiencies are noted which might not have been present at the time of construction. Changes in the condition of the site should also be noted such as:

• Erosion

• Scour

• Re‐grading of slopes

The final new bridge completion checklist should include the notification of HIB R&B Department Engineer when the bridge is opened to traffic and available for use by permit vehicles. The opening of a new bridge, particularly an off‐system bridge, is a good time to ensure that a set of copies of the bridge plans are included with the Bridge Records. RBD require all Contractors to submit a copy of the final structural plans to RBD within 31 days after construction or rehabilitation is completed. The initial Bridge Folder is prepared as a result of the Initial Inspection. A detailed description of the Bridge Folder contents is given in Chapter 7, Bridge Records. The arrangement of the folder shall be maintained and must include the recommended series of photos.

13.3.3 Routine Inspections Routine inspections are those regularly scheduled, performed, and recorded in accordance with all the procedures described in subsection 13.7, Bridge Records, and the instructions for the coding guide. These are usually done every two years for most bridges and every four years for culverts. Inspection Equipment The equipment needed for routine bridge inspections usually includes the following:

• Cleaning tools including wire brushes, screwdrivers, brushes, scrapers, etc.


• Inspection tools including pocket knife, ice pick, hand brace, bit, chipping hammer, etc.

• Visual aid tools including binoculars, flashlight, magnifying glass, dye penetrant, mirror, etc.

• Basic measuring equipment including thermometer, center punch, simple surveying equipment, etc.

• Recording materials such as appropriate forms, field books, cameras, etc.

• Safety equipment including rigging, harnesses, scaffolds, ladders, bosun chairs, first‐aid kit, etc.

• Miscellaneous equipment should include C‐clamps, penetrating oil, insect repellant, wasp and

hornet killer, stakes, flagging, markers, etc.

• Specialized measuring tools such as paint film gage, calipers , optical crack gage, tiltmeter, SHIFLO, etc. The SHIFLO is a device used to measure the depth of scour during flood flows with a depth finder. It is not used during Routine Inspections.

• Underwater Inspections may require the use of Scuba gear.

Inspections which may significantly interfere with normal traffic movement and which might affect the safety of the inspectors must be coordinated with Traffic Authorities in order that appropriate traffic control measures may be undertaken. Inspections of the underside of bridges that cannot be reached by conventional ladders may be performed by the use of vehicles with under‐bridge platforms. Interim Inspections Brief inspections are also performed by Bridge Inspection Engineers approximately every six months on most structures to identify unusual conditions or changes. These inspections do not review all the points of interest done in a normal Routine Inspection. No formal records are kept of these brief inspections. However, unusual conditions or changes will often result in a follow‐up In‐Depth, Damage, or Special Inspection

13.3.4 Damage Inspections Damage Inspections are those performed as a result of collision, fire, flood, significant environmental changes, loss of support, etc. These inspections are also sometimes called Emergency Inspections and are performed on an as‐needed basis.

13.3.5 InDepth Inspections Reasons for InDepth Inspections In‐Depth Inspections are usually performed as a follow‐up inspection to an Initial, Routine, or Damage Inspection to better identify any deficiencies found. Underwater Inspections and Fracture‐Critical Inspections are both types of In‐Depth Inspection. These


are described in more detail below. Load testing may also sometimes be performed as part of an In‐Depth Inspection. However, load testing for determining bridge load capacity is costly and interpretation of the results are sometimes open to question. Underwater Inspections Underwater Inspections are a type of In‐Depth Inspection. These are regularly performed every five years. The frequency can be less than five years if conditions warrant. A master list of bridges needing underwater inspections is compiled and updated during routine inspections. Once a bridge is added to the master list, it will remain there until it is no longer in use. Some bridges must be inspected at intervals more frequent than the required five years due to the susceptibility to scour or other factors such as the age of the bridge, configuration of the substructure, environment, adjacent features, or existing damage. The frequency, type, and level of inspection are left up to the owner. Underwater Inspection Methods There are currently three methods used to conduct Underwater Inspections. These are:

o Wading ‐‐ The most basic of the three methods, wading requires only a probing rod and wading boots to be effective.

o Scuba diving ‐‐ A method that allows a more detailed examination of substructure

conditions at the Mud‐line. The diver has freedom of movement and may carry a variety of small tools with which to probe or measure.

o Hardhat diving‐‐ Involves the use of sophisticated diving equipment and a surface

supplied air system. This inspection method is well suited when adverse conditions will be encountered, such as high water velocity, pollution, and unusual depth or duration requirements.

The choice of which method to employ depends largely on accessibility and the required inspection detail. Levels of Underwater Inspection Standard levels of inspection are:

o Level I ‐‐ Consists of a simple visual or tactile (by feel) inspection, without the aid of tools or measuring devices. It is usually employed to gain an overview of the structure and will precede or verify the need for a more detailed Level II or III inspection.

o Level II ‐‐ A detailed inspection which involves physically cleaning or removing growth

from portions of the structure. In this way, hidden damage may be detected and


assessed for severity. This level is usually performed on at least a portion of a structure, supplementing a Level I.

o Level III ‐‐ A highly detailed inspection of an important structure which is warranted if

extensive repair or replacement is being considered. This level requires extensive cleaning, detailed measurements, and testing techniques that may be destructive or nondestructive in nature.

Underwater Structural Elements The elements of a bridge structure that may be located below the water line are abutments, bents, piers, and protection systems. Bents are distinguished from piers in that they carry the loads directly to the foundation, rather than using a footing. Abutments normally do not require an Underwater Inspection, but in rare instances may be continuously submerged. Although usually founded on piles or drilled shafts, abutments occasionally rest on spread footings in rock. Scour is almost always the primary consideration when an underwater abutment inspection is being conducted. Local scour is often detectable during diving inspections, although sediment will eventually refill a scour hole between the events that cause the scour. More general scour, or channel degradation, will usually be undetectable to the diver and must be determined from known channel cross sections or historical data. Underwater Inspection Devices There are several types of sounding or sensing devices available for use by divers in underwater investigations. Most common is the black and white fathometer, which uses sound waves reflected from the channel bottom and records the depths continuously on a strip chart. It provides an inexpensive, effective means of recording channel depths but will not detect a refilled scour hole. Other methods are color fathometers, which use different colors to record different densities and in this way can often detect scour refill; ground penetrating radar, which works well for shallow water but has limited usefulness in murky water; and fixed instrumentation, which is reliable but requires periodic monitoring and resetting to be effective. Underwater Structural Materials Piers and bents, if located in a navigable waterway area, are often subject to material defects or collision damage as well as scour. Concrete is the most common type of material encountered in underwater inspections. Common defects in concrete substructures include cracking, spalling, laitance, and honeycombing. Minor or even moderate damage to concrete can be tolerated if it does not endanger the reinforcement. Corrosion of the reinforcement can lead to serious difficulties. Steel substructures are very susceptible to corrosion near the waterline or between the high and low water levels. In this area, the presence of oxygen and frequent wet/dry cycles promote deterioration at an accelerated rate and steel should be measured to determine the possibility of section loss.


FractureCritical Inspections Fracture‐Critical Inspections are a type of Special Inspection. These inspections are usually limited to non‐redundant tensile stress areas. They are regularly performed every five years. The frequency can be less than five years if conditions warrant. Methods of inspection may include dye penetrant, magnetic particle, or ultrasonic techniques. History of Fracture Critical Considerations Early development of modern steel design focused on stress and strain; little was known or recognized about the potential adverse effects of multiple stress cycles. Early materials such as wrought iron were not capable of great unit strength. Early designs lacked the sophistication that would require a designer to closely address details. Even after the introduction of electric arc welding in the 1880s, most steel bridges were simple‐span, composed of built‐up and riveted members. Design of continuous beam highway bridges began after welding technology was improved. The result of the use of continuity was more flexible structures that were more subject to deflections and rotations. The result of the use of welding, was simpler bridges and more consistent construction quality. As steel production and availability improved, along with higher strength steels, design engineers were quick to accept the obvious benefits. However, no material is perfectly homogenous, and the fact that steel could have hidden flaws was essentially ignored by designers. After World War II, there was a massive expansion of highway bridge construction. The popularity of personal motor vehicles increased as a result of more highways and thus more highways and bridges were needed. The construction material of choice was initially steel throughout much of the country. Many designed smaller structures with concrete, which is still serving well in many cases. Steel bridges, particularly trusses, were used for longer crossings, usually for streams and rivers. Fatigue Failures The Truss Silver Bridge at Point Pleasant, West Virginia , USA collapsed suddenly in 1967 due to the brittle fracture of an eye bar link, resulting in the loss of 46 lives and closure of a major route. After the failure, significant additional research efforts were initiated in fracture mechanics. As a result, the effects of multiple stresses at less than yield of the materials were understood more thoroughly. The first recognition of redundant and non‐redundant members was presented in the 12th edition of the AASHTO Bridge Specifications in 1977 . The first guide specifications for fracture critical bridge members were issued by AASHTO in 1978. FractureCritical Members After design engineers began to recognize the problems associated with multiple stresses at less than allowable values, further information was developed to assist in the design process and in evaluation of existing structures. After notable failures, it was recognized that many existing bridges may be nearing failure due to fatigue. Fracture‐Critical (FC) members were recognized and defined as a member or component whose failure in tension would result in the collapse of a bridge. These are commonly


referred to as non‐redundant members. Methods were developed to help determine which structures must be further evaluated by designers for susceptibility to fatigue problems. Designers began to include Fracture Control Plans (FCP) in bridge design details. Most common types of FC members are tension flanges and sometimes parts of webs of flexural members such as beams and girders. Tension members of trusses, particularly eye bars, which commonly make up the lower chords of old trusses, can also be FC. Other tension members of trusses, such as diagonals, are also FC. Concrete members are not often used in tension. The design of flexural concrete members with multiple reinforcing bars precludes possibility of abrupt failure due to their internal redundancy. The following rules‐of‐thumb usually determine FC members:

• Two‐girder bridges are defined as FC. Fracture of lower flanges in positive moment areas (mid spans) and upper flanges in negative moment areas (over supports) can be expected to lead to collapse of the structure. However, cracks over interior supports sometimes lead to subsequent higher positive stresses in the spans with no catastrophic collapse. Therefore, these FC components receive more frequent periodic In‐Depth Inspections.

• All steel caps are defined as FC. While this statement is bold, an exception is difficult to imagine.

• Lower chords of trusses are FC. This determination is based on the fact that most truss bridges

employ only two trusses and most are simple span.

• Secondary members such as diaphragms and stiffeners are not FC. They are rarely used in a manner where failure would lead to structure collapse. However, caution must be observed in evaluating certain truss members that may appear to be secondary when in fact their attachment to main FC members can provide a starting place for the main member failure.

Redundancy The concept of structural redundancy is well known. Any statically indeterminate structure may be said to be redundant, to varying degrees, depending upon its supports. A two‐span straight girder is redundant. However, a two‐span curved girder is also redundant, but the support reactions are determinate. These definitions of redundancy are of little value to the field inspector who must make a determination of FC potential for various members in a bridge. There are two types of redundancy that concern the FC inspector:

• Load Path Redundancy. Superimposed traffic loads are supported directly by the deck, which in turn is supported by longitudinal stringers or beams. A bridge with a single box girder would therefore be non‐redundant since a failure in the box would collapse the bridge. Likewise, a two‐girder bridge is non‐redundant since one girder cannot assume all of the load for which two are designed. However, it can be argued that a continuous two‐girder bridge is structurally redundant since a girder failure would not cause collapse, but the structure would sag excessively. Three or more girders will usually have enough load capacity due to inherent design factors of safety to avoid collapse. The failure of one girder will immediately cause the loads to be shared by the other


girders. However, the FHWA considers three‐girder bridges with more than 4.60 M girder spacing to be FC. The strength of the deck system should be considered for this case. Some deck systems for wide beam spacings are two‐way slabs and others have stringer and floor beam systems with one‐way slabs. Those with two‐way slabs will still have a load‐path redundancy, while those with stringers and floor beams will be more unstable after failure of one girder in a three‐girder system.

• Internal Redundancy. This term refers primarily to built‐up members, such as riveted

plate girders. A single plate or shape in the built‐up member might fail without causing collapse. However, even members such as this must sometimes be considered non‐redundant, since like two‐girder structures, failure of one portion of the member can overload the remaining portions such that there is not sufficient remaining capacity to prevent total failure. Usually, if the cross‐sectional area of the largest shape or plate in a built‐up member is less than about 30 to 40 percent of the total member area, then the member may be considered to have internal redundancy.

Inspection Procedures for FC Members Inspection procedures begin with proper advance planning. The more important planning aspects, usually based on an office review of the structural plans, are:

• Identify possible FC members.

• Note the particular members in the structure that may require special field attention, such as built‐up tension members composed of few individual pieces.

• Pre‐plan necessary access to the members, including special equipment needs such as ladders,

bucket truck, or climbing gear.

• Many FC members are a result of structures designed for urban situations with necessary complex alignment geometries. Proper inspection of these bridges may require closing a traffic lane. Safe traffic control must be coordinated in advance with RBD and the Traffic Authorities.

• If the structure involves a railroad, a railroad flagger must be coordinated with the proper

railroad company.

• Identify and make available any necessary special tools and equipment that may be required in addition to the normal inspection gear. A high‐pressure washer is often useful in cleaning areas where a large accumulation of debris might obscure view of FC areas. Non‐destructive test equipment such as ultra‐sonic devices may be advantageous in some areas, particularly inspection of box‐type bent caps and pin‐and‐hanger connections.

The actual field inspection of all FC members consists of several steps. The most important step is a visual inspection. The inspector notes any:

• Visual cracks and their direction and location


• Evidence of rust, which may form at a working crack

• Weld terminations in a tension area

• Interrupted back‐up‐bars used for built‐up‐member fabrication

• Arc strikes, scars from assembly cables or chains, or other physical damage

• Cross‐section changes which may cause a sudden increase in the stress pattern Fatigue and Fatigue Fracture Members subjected to continued reversal of stress, or repeated loading such that a range of change in stress occurs, are subject to a behavior called fatigue. Members that have a relatively constant, steady stress are not subject to fatigue. The term has been in use for almost a century and is currently defined by the American Society of Testing Materials

(ASTM 1823‐96e1) as “the process of progressive localized permanent structural change occurring in a material subjected to conditions that produce fluctuating stresses and strains at some point or points and that may culminate in cracks or complete fracture after a sufficient number of fluctuations.” Fatigue can result in:

• Loss of strength

• Loss of ductility

• Reduced service life Fatigue fractures are the most difficult to predict since conditions producing them are often not clearly recognizable. Fatigue occurs at stress levels well within the elastic range, that is, less than the yield point of the steel, and is greatly influenced by minor imperfections in the structural material and by fabrication techniques. Fatigue fracture occurs in three distinct stages:

• Local changes in atomic structure, accompanied by sub‐microscopic cracking

• Crack growth

• Sudden fracture FatigueProne Details Fatigue fracture almost always begins at a visible discontinuity, which acts as a stress‐raiser. Typical examples are:

• Design details such as holes, notches, or section changes


• Flaws in the material such as inclusions or fabrication cracks

• Poor welding procedures such as arc strikes

• Weld terminations

Certain structural details have been long recognized as stress‐raisers and are classified as to their potential for damage. These details appear in the current AASHTO Bridge Specifications, HIB Bridge Manual and other technical publications. Most of these common details should be familiar to the fracture critical bridge inspector. Proper consideration of member detail and sizing during design will help control stress level and thus control crack growth. The stress range, or algebraic difference in the maximum and minimum stress, also becomes important. The most effective way to control cracking and eventual fracture is sensible detailing. Details such as out‐of‐plane bending in girder webs and certain weld configurations can cause crack propagation and fracture. Design for fatigue also includes observing a fracture control plan (FCP). The FCP identifies the person responsible for assigning fracture‐critical designations. It establishes minimum qualification standards for welding personnel and fabrication plants. It also sets forth material toughness and testing procedures. The specific members and affected sections are also identified in the FCP. During fabrication, these members are subject to special requirements. Fatigue failure is always an abrupt fracture, called a brittle fracture. A brittle fracture is distinguished from a ductile fracture by absence of plastic deformation and by the direction of failure plane, which occurs normal to the direction of applied stress. Other failure surfaces due to high stress are usually at an angle to the direction of the stress and are often accompanied by a narrowing or necking of the material. Brittle fracture failures have no narrowing or necking present. The three main contributing factors to brittle fracture are:

• Stress level

• Crack size

• Material toughness, sometimes called fracture toughness

Small, even microscopic cracks can form as a result of various manufacturing and fabrication processes. Rate of propagation, or growth, of cracks also depends on the stress level and the material toughness. Material toughness is the ability of a material to resist brittle fracture. This resistance is primarily determined by chemical composition and to some extent by the manufacturing processes. Usually, higher strength steels are more susceptible to brittle fracture and have lower toughness. Toughness can be improved by techniques such as heat treatment or by quenching and tempering.


Weld Details Inspectors concerned with FC inspections must acquaint themselves with the characteristics of good and poor structural details and be able to identify those details in the field. Welding creates the details most susceptible to fatigue and fracture. Therefore, it is imperative to recognize features prone to FC failure. Major FC problem areas are at weld discontinuities or changes in geometry such as:

• Toes of fillet welds

• Weld termination points

• Welds to girder tension flanges from other connections such as stiffeners or diaphragms

• Ends of welded cover plates Welded cover plates on rolled beams were a very common detail until fatigue failures began to be recognized by bridge engineers. Whether the weld is terminated or continued around the end of the cover plate, the condition is at best Category E. Weld attachments to a girder web or flange can reduce fatigue strength as the length of the attachment increases. Welds two inches or less fall in Category C and those greater than four inches in length reduce to Category E. Such details are commonly used to attach diaphragms and wind bracing to maintain structural members, either at the flange or web. Details such as run‐off tabs and back –up bars may also provide possible stress riser discontinuities if not smoothed by grinding after removal. Inspectors should familiarize themselves with acceptable and unacceptable fillet weld profiles in order to recognize potential problem areas in the field. Fatigue in Secondary Members Secondary members may also have fatigue problems. For instance, main girder stress reversal may induce vibrations in lateral bracing or diaphragms. In many cases the number of stress reversals in the secondary member is a magnification of those stresses in the main member. The attachment of plates to a girder web may cause out‐of‐plane bending in the web, a situation not usually considered by the designer. In general, secondary members themselves are not subject to a FC inspection. However, some secondary members, even though designed only as secondary members, such as lateral wind bracing in the lower plane of a girder system, will act as primary members. These cases generally occur in curved or heavily skewed structures. A curved bridge will have twisting or torsional effects due to the live loads that are partially resisted by the diagonal lateral wind bracing. These braces, particularly those near supports, should be inspected for possible fatigue cracks. Proper Welding and Repair Techniques Proper welding of structural steel members is a tedious process under the very best of conditions, which


are usually found in the fabrication shop. Any field welding, whether it is a welded girder splice, retrofit detail, or repair, should be closely examined for visible problems. Many shop splices are accomplished by automatic welding machines under controlled conditions and can be smoothly ground to eliminate surface discontinuities. Field splicing operations are subject to exposure to the elements and difficulties in stabilizing the pieces to be joined. In addition, the welding is usually done by hand and therefore subject to human error. Welded field splices for bridges should be subject to careful inspection and must be done by certified welders. The welded field splices for these bridge are usually of the same quality as shop splices and are often further inspected by radiographic (X‐ray) techniques. The inspector should also be aware of problems that may arise from the use of improper field repair processes. Often a well‐intentioned repair can actually make a member even more susceptible to brittle fracture. FC Inspection Techniques FC inspection techniques may include non‐destructive testing to determine the condition of a structural member. There are several types available, including radiographic, ultrasonic, dye penetrant, and magnetic particle inspection. All are acceptable methods, but each has limitations and may not be suitable for a particular situation. One single technique may not be sufficient to assess damage and a combination of more than one may be advisable. Usually these types of inspection are best left to personnel who have undergone the proper training. The selection of the type of non‐destructive testing method for a particular location is usually a function of the detail. For instance, potential cracks at the ends of welded cover plates are often inspected by the use of radiographic methods. Cracks in pins are best inspected by ultrasonic techniques. Subsurface defects such as inclusions may be found by magnetic field irregularities, and cracks adjacent to fillet welds at tee‐joints are usually inspected by dye penetrant.

13.3.6 Special Inspections Special Inspections are performed to monitor new types of structures, structure details, or materials. A Special Inspection may also be used to help develop an information database. An example of a Special Inspection is the inspection of the grouted ducts in externally post‐tensioned members of pre‐cast segmental type bridges. 13.4 Ratings and Load Posting

13.4.1 Overview This Section includes discussion of the following topics:

• Condition Ratings

• Appraisal Ratings


• Load Ratings

• Legal Loads

13.4.2 Condition Ratings

Definition of Condition Ratings Condition Ratings based on the field inspections can be considered as “snapshots in time” and cannot be used to predict future conditions or behavior of the structure. However, the Condition Ratings based on the inspections along with the written comments by the field inspector act as the major source of information on the status of the bridge. The Condition Ratings also help in planning for any necessary repairs or modifications. In addition, the Condition Ratings are used as flags when performing overweight permit evaluations. Condition Ratings are one‐digit numbers given by the field inspector to the various components of a bridge. They are intended to be objective and not distorted by personal beliefs or opinions. There is significant emphasis to have the Condition Ratings be more consistent between inspectors given the same deficiency of structural component. Condition Ratings are a measure of the deterioration or damage and are not a measure of design deficiency. For instance, an old bridge designed to lower load capacity but with little or no deterioration may have excellent Condition Ratings while a newer bridge designed to modern loads but with deterioration will have lower Condition Ratings. The channel, waterway, riprap, and other channel protection components under and directly upstream and downstream of the bridge are often inter‐related to one another in assigning the Condition Rating for the channel. Recording Condition Ratings Condition Ratings are entered on the Bridge Inspection Record, BIR. There are six component items covered on the form, each of which lists four to 11 elements. The Item Numbers relate to the entry of the data in the electronic Bridge Inventory Files, the detailed instructions for which are contained in the instructions for coding guide. The six component items plus a miscellaneous item are:

• Deck (Item 58)

• Superstructure (Item 59)

• Substructure (Item 60)

• Channel (Item 61)

• Culverts (Item 62)

• Approaches (Item 65)


• Miscellaneous (used for information, but not entered in the Bridge Inventory file. Still important

as part of the Bridge Folder).

The elements for each component have minimum values (shown to the left of the element description on the BIR Form that the rating must equal or exceed. Each element is rated based on independent consideration. For instance, poor or deficient secondary members (bracing, diaphragms, etc.) in a superstructure may cause the Superstructure (Item 59) component to have a poor rating even though there is no significant deterioration of the main members. The summary Component Rating must be the least of the element ratings comprising that component. However, it should be noted that Deck (Item 58) component is independent of its associated element ratings such as joints, railings, wearing surface, etc. The known presence of chlorides in the deck, superstructure, or substructure concrete or low compressive strengths from cores should not influence Condition Ratings. The Condition Rating should be determined solely on the observed, materials‐related, physical condition of the component at the time of the inspection. The BIR Form has page/s for fully supportive written comments for each of the above features. These comments are required for any Condition Rating of 7 or less. The form includes a brief summary of the description of each level of rating. More detail on the Condition Rating for each Item Number is given in the instructions for coding guide. Assigning Condition Ratings The general considerations for assignment of the ten levels of Condition Ratings require that each element be evaluated separately. However, other deficiencies may affect the condition if they are directly related. For instance, instability of an approach embankment may reduce the abutment Condition Rating but not reduce the Superstructure Condition Rating. Only permanently installed repairs are to be considered when assigning Condition Ratings. Permanent implies that the repair has returned the damaged or deteriorated element to a condition as good as or better than the remainder of the bridge. For instance, a steel beam damaged by an over‐height load that reduced the load capacity of the beam is considered permanently repaired when a section is replaced or a bent section is straightened by proper techniques and no residual cracks can be found. The strength of the repaired member is the primary concern. Modifications and repairs that simply improve the appearance of a damaged member should not be considered to improve the Condition Rating. Components with temporary repairs, even though functioning, should not be considered for Condition Rating. For instance, a support or brace to a partially undermined column could be susceptible to damage from another flood; therefore, the Condition Rating must be made on the basis that the support is not present. Temporary repairs must not be considered in determining Condition Ratings because they directly affect the calculations of the Sufficiency Ratings that are described in Chapter 7.


Condition Ratings are still a matter of judgment, which should be made based on experience, knowledge, and consistency with other structures with the same deterioration.

13.4.3 Appraisal Ratings Definition of Appraisal Ratings Appraisal Ratings consider the field condition, waterway adequacy, geometric and safety configurations, structural evaluation, and safe load capacity of the bridge. As for Condition Ratings, they should be as objective as possible. Given the same field information, project plans, materials, geometric, and waterway data, the same Appraisal Ratings should result independent of the appraiser. Seven features are evaluated for their effect on the safety and serviceability of the bridge and its approaches. The intent is to compare the bridge to a new structure built to current standards. Appraisal Ratings are usually done in the office where access to all necessary information and specifications is available. However, an experienced Bridge Appraiser may make some appraisals in the field while performing the duties of a Bridge Inspector. Recording Appraisal Ratings As an aid in recording the features, instructions are given on the Bridge Appraisal Worksheet, (BAW). The Item Numbers are related to the entry of the data in the bridge inspection database. The detailed instructions for entering data are contained in the instructions for coding guide. The seven features are:

• Traffic Safety Features (Item 36)

• Structural Evaluation (Item 67)

• Deck Geometry (Item 68)

• Under‐clearances (Item 69)

• Bridge Posting (Item 70)

• Waterway Adequacy (Item 71)

• Approach Roadway Alignment (Item 72). The Bridge Appraisal Worksheet has space for fully supportive written comments for each of the above features. These comments are required even for features with no deficiency. The following paragraphs summarize instructions for coding the above seven features. Traffic Safety Features (Item 36). This feature applies only to bridges carrying vehicle traffic. It is a measure of the adequacy of traffic safety features in meeting current acceptable standards, which reflect modern design criteria. Four


digits are assigned that approximately measure the adequacy the traffic safety feature. The first digit is for the Bridge Railings, the second digit is for the Guardrail to Bridge Railing Transitions, the third digit is for Approach Guardrails, and the fourth digit is for Guardrail Terminals. Each of these four parts to Item 36 is assigned a value of 1 if it meets currently acceptable standards, a value of 0 if it does not, or a value of N if not applicable. Note that these values do not give a true measure of the comparative strength or crash test level for the traffic safety feature. Collision damage or deterioration is not considered when assessing traffic safety acceptability. It must be assumed that damage to traffic safety features will be repaired in the near future. Bridge class culverts do not require coding of traffic safety features if the headwall of the culvert is 9.0 M or more from a traveled lane. If there is zero to 1.0 M of fill over a culvert, and acceptable guard fence is installed over the culvert and along the approaches, then bridge railings and transitions are not required. Culverts with less than 1‐meter of fill may also have guard fence instead of bridge railing if the steel posts are properly attached to the culvert. Acceptable traffic safety standards have been developed using the current AASHTO Standard Specifications for Highway Bridges and the AASHTO Guide for Selecting, Locating, and Designing Traffic Barriers.

Current acceptable bridge railing details are shown in the HIB Bridge Manual. Structural Evaluation (Item 67). This feature considers major structural deficiencies and is based on the Condition Ratings of the Superstructure (Item 59), the Substructure (Item 60), and the Inventory Rating (Item 66) as related to the Average Daily Traffic (Item 29). Items 66 and 29 are correlated in a table included with the detailed instructions for Item 67 in the instructions for coding guide. The Structural Evaluation Appraisal Rating should generally be no higher than the lowest of the Superstructure or Substructure Condition Ratings or the Inventory Rating ‐ ADT correlation. Deck Geometry (Item 68). This feature applies only to bridges that carry vehicle traffic. Roadway widths are measured perpendicular to traffic direction and between faces of railings, curbs, and median barriers. Mountable curbs are ignored if 100mm or less in height. The Deck Geometry Appraisal Rating is determined from a four‐part table included with the detailed instructions for Item 68 in the “Instructions for Coding Guide”. This table relates the ADT (Item 29), Bridge Roadway Width (Item 51), and Number of Lanes (Item 28). This Appraisal Rating is further controlled by another table in the instructions for Item 68 in the “Instructions for Coding Guide” that relates the Minimum Vertical Clearance (Item 53) and the Functional Classification (Item 26) of the bridge. The Deck Geometry Appraisal Rating is taken as the lowest number based on width, lanes, or vertical clearance and Functional Classification of the highway on which the bridge is located.


Underclearances (Item 69). This feature is a measure of both vertical and lateral clearances for any roadway or railroad passing under the bridge being rated. The vertical clearance is measured down from the lowest part of the bridge to the lower traveled roadway surface (excluding paved shoulders) or top of railroad rails. The Under‐clearances Appraisal Rating is determined from two tables included with the detailed instructions for Item 69 in the “Instructions for Coding Guide.” These tables relate the Vertical Under‐clearance (Item 54) and the Functional Classification (Item 26) of the lower roadway or railroad, and the Lateral Under‐clearances Right and Left (Items 55 and 56) of the lower roadway or railroad. The Under‐clearances Appraisal Rating is taken as the lowest number based on the vertical and lateral clearances and the Functional Classification of the lower roadway or railroad. Bridge Posting (Item 70). This feature compares the load capacity of the bridge to the State Legal Load. At this time, the term “ Legal Load” is assumed to be a load equivalent to the conventional HS‐20 load pattern as shown in Figure 5‐1. Therefore, any Inventory Rating less than HS‐20 requires further evaluation of the bridge. Bridges are normally not load restricted unless the capacity is less than an HS‐20 Operating Rating. The need for load restriction will be explained in more detail in the section of this chapter titled Legal Loads and Load Posting. Specific criteria for coding this Appraisal Rating are included with the detailed instructions for Item 70 in the “Instructions for Coding Guide,” which has five posting levels. The Bridge Posting Appraisal Rating is 5 if the Operating Rating (Item 64) is more than HS‐20. The Bridge Posting Appraisal Rating has a value of 0 to 4 depending on the percentage the Operating Rating is below the State Legal Load, which for this item is taken as HS‐20 loading.


Waterway Adequacy (Item 71). This appraisal feature applies to all bridges carrying vehicle traffic over any type of waterway. It represents the capacity of the waterway opening to carry peak water flows and is based on the criteria included with the detailed instructions for Item 71 in the “Instructions for Coding guide” which has eight values range from 2, meaning the bridge is frequently overtopped by flood waters, to 9, meaning that chance of overtopping is remote. The estimated potential for traffic delays from flood overtopping is also considered when assigning a value to waterway adequacy. The design flood is the maximum water flow that can pass under bridge for a given recurrence frequency, usually expressed in years.


When hydraulic information is unavailable, the design flood is assumed to be equal to the frequency of overtopping the bridge. Local officials and residents can often provide information on the frequency of overtopping. Approach Roadway Alignment (Item 72). This feature applies to adequacy of the approach roadway to safely carry vehicle traffic considering both horizontal and vertical alignments. Specific criteria are included with the detailed instructions for Item 72 in the instructions for coding guide. Approach curvature, lane and shoulder widths, surface roughness, and sight distances all enter into the evaluation of this Appraisal Rating. For bridges on crest or sag vertical curves, consideration must also be given to headlight and stopping sight distances. When approach alignment is questionable, the inspector should drive the alignment on the approaches to the bridge in order to estimate an advisory safe speed with due consideration given to minimum sight distances. Advisory speed on approach curves is the speed above which more than usual concentration and effort on the part of a normal driver would be required to remain safely in the proper lane. Advisory speed limit should be taken as the posted advisory speed if one exists.

13.4.4 Load Ratings

Definition of Load Ratings The Load Rating is a measure of bridge live load capacity and has two commonly used categories:

• Inventory Rating, as defined by the current AASHTO Manual for Condition Evaluation of Bridges, is that load, including loads in multiple lanes, that can safely utilize the bridge for an indefinite period of time.

• Operating Rating, defined by the same manual, is the maximum permissible live load that can be

placed on the bridge. This load rating also includes the same load in multiple lanes. Allowing unlimited usage at the Operating Rating level will reduce the life of the bridge.

Determination of Load Ratings Currently, all Inventory and Operating Ratings are expressed in terms of an equivalent HS‐truck as shown in the AASHTO Manual for Condition Evaluation of Bridges. Prior to about 1995, many ratings

were for an equivalent H‐truck, shown in AASHTO Manual for Condition Evaluation of Bridges.

The H‐truck directly corresponds to single‐unit trucks, which used to be common on rural highways. Today, even rural Farm‐ or Ranch‐to‐Market highways and many off‐system highways are exposed to much larger semi‐trucks; therefore, the HS‐truck is more realistic. Inventory or Operating Ratings are usually determined using either Load Factor (LF) or Allowable Stress (AS) methods. Since 2000, LF is to be used for all on‐system bridges. Either AS or LF may be used for all off‐system bridges.


Inventory Rating and Design Load Considerations The Inventory Rating (Item 66) can usually be initially estimated to be at least equal to the design loading if no damage or deterioration exists and the original design was made using an HS load pattern. Many old plans have a design loading shown as H‐20 S‐16 which some raters have misinterpreted as meaning H‐20. AASHTO replaced the H‐20 S‐16 designation in 1965 with the HS‐20 designation. Re‐rating these bridges using LF procedures will usually increase the Inventory Rating above HS‐20. Some newer bridges have been designed on a case‐by‐case basis for higher design loads, but HIB bridge design practice is still to design to the HS‐20 loading. Design Supplement The primary subjects of the supplement that affected bridge design can be summarized as follows:

o Crown Width Bridges. The 1944 AASHTO Bridge Specifications required curbs on all bridges. Bridge curbs may be omitted provided the guard fence or an equivalent member is carried continuously through the structure.” The 1949 AASHTO Bridge Specifications

allowed the condition of no curbs with certain additional width limitations.

o Design Overload. The 1944 AASHTO Bridge Specifications required an overload to be

considered for all bridges designed for less than an H‐20 (18.20T) or H‐20 S‐16 (32.70T) loading, now called HS‐20 loading. The overload was to be the design truck (usually H‐15) increased by 100 percent, but without concurrent loading of adjacent lanes, thus allowing single‐lane load distribution. The allowable stress was to also be increased to 150 percent of the basic allowable. This provision can be modified specifically to apply the same overload to truss counter members for all design loadings. Truss counters are those members that, for some positions of live load, will change from tension to compression. If a truss was designed H‐15, H‐20, or H‐20 S‐16, the overload was applied in determining the size of counter member.

o Lane Load Negative Moments. The 1944 AASHTO Bridge Specifications required for H‐10, H‐15, or H‐20 lane loads an additional concentrated load in one other span in a continuous unit positioned to produce maximum positive and negative moments. The distance between the concentrated loads for the lane load is limited to a maximum of 9.20M. This is probably based on the fact that the AASHTO 1944 Bridge Specifications did not require an additional concentrated load for H‐20 S‐16 lane loadings. The H‐20 S‐16 truck loadings have a second axle spaced from 4.30 M to 9.20 M from the first heavy axle. The 1949 AASHTO Bridge Specifications made the lane loading negative moment requirement the same for HS‐trucks. The provision for continuous spans subjected to lane load can be modified by limiting the spacing between the additional concentrated load to 9.20 M. This limit had the effect of reducing the lane load negative moment maximums for some continuous spans. The 9.20 M‐ limit may also have been in recognition that the second large axle for an HS‐load pattern is spaced at a maximum of 9.20 M from the first large axle, or it might have been because the lane load


approximately represents a train of trucks with a headway distance of 9.20 M between trucks. It would have been more logical for the second concentrated load to be placed a minimum of 9.20 M from the first instead of a maximum of 9.20 M. Current specifications do not limit the distance between the two loads for negative moment lane loadings.

o Impact Load Provision. The 1944 AASHTO Bridge Specifications required that the

shortest length of adjacent spans in a continuous unit be used for the negative moment impact value. In 1949, AASHTO changed this to the current provision of using the average length of the adjacent spans. Both versions of The impact provision for continuous units or other structures where discontinuous lane loadings are applied to be the loaded length as indicated by the influence line for the section of member considered had the effect of slightly increasing the impact value.

o Special Axle Loads. The AASHTO Bridge Specifications further limited the 11.00 T axle

to slab spans under 5.50 M and the two 7.30 T axles for slab spans over 5.50 M. This provision had the effect of reducing the design load for many slab spans designed during that time. Some beams have been designed using the single 11.00 T axle. It is believed to be an error for beams to have been designed this way. For this reason, any plans prepared with a design load of H20 or H20 S16 should be carefully evaluated.

Customary Rating Procedures The initial load rating should always be re‐calculated; the design loading should not be used as the final Inventory Rating. When a bridge was originally designed, the designer often had to select the next size of reinforcing bar, size of steel beam, or thickness of cover plate to meet the design stress criteria. Sizes that were larger than the theoretically perfect size of member result in Inventory Ratings significantly higher than the design loading. However, the design loading and date of original construction is an important part of the bridge data since they often provide a basis for determining initial routing of overload permits. If the original design was made using an H‐load, such as H‐15, or H‐20, then the equivalent HS Inventory Rating will usually be significantly less numerically. For example, an H‐15 design might rate at HS‐12. However, this difference means that the total inventory HS‐load capacity is 19.60 Tons (two 8.70 T axles and one 2.20 T axle totaling 21.80 Tons) as compared to the H‐15 design of 13.60 T. Bridge designs made using AS procedures with an allowable of 5 percent overstress for some components are to be re‐analyzed using LF procedures. AS rating procedures are usually set at 55 percent of the material yield stress for steel structures and 50 percent of the material yield stress for Grade 40 reinforcing steel in concrete structures. When AASHTO first introduced the use of Grade 60 reinforcing steel in the 1970 Interim Bridge Design Specifications, the allowable of 165.40 MPa for Grade 60 was assigned based approximately on the ratio of the Grade 60 ultimate strength to that of Grade 40. Thus the AS procedures were still compatible in factor of safety for concrete members.


LF rating procedures usually assign a dead load factor of 1.3 and live load factors of 2.17 (when computing Inventory Ratings) and 1.3 (when computing Operating Ratings). The resulting stresses or bending moments are compared to the yield of steel members or the ultimate capacity of concrete members also considering appropriate phi strength reduction factors. Note that the value of 2.17 is the dead load value of 1.3 times 1.67. The load factor of 1.3 accounts for a 30 percent increase in all loadings, either dead or live, so as to provide a uniform safety factor. The factor of 1.67 accounts for the variability of live load configurations other than a standard HS‐load pattern and further provides for potential overloads. See Subsection 13.4, Legal Loads. Specific analysis of structures for overweight loads, particularly super‐heavy permits over about 127.30 Tons, is usually done with a load multiplier consistent with the restricted speed of the vehicle. Commonly this factor is about 1.1, with total stresses compared to an allowable of 75 percent of the yield for steel bridges or 75 percent of the ultimate capacity for concrete bridges including pre‐stressed beam bridges. This procedure is explained more fully in subsection 13.6, Routing and Permits. Temporary repairs must not be considered for Inventory or Operating Ratings. However, temporary repairs are taken into account when assigning the operational status code of Item 41 to the structure. Temporary repairs are to be considered for the operational status code only until a more permanent repair is made and should not be used for more than four years. The Inventory Rating directly affects the Sufficiency Rating, and therefore temporary repairs must not be assigned any weight in the Load Rating calculations. When the design loading is unknown or deterioration exists, load rating calculations must use all field information and conventional analysis techniques. Even when the design loading is known, the only acceptable method for accurate load rating is to do calculations based on the plans and known field measurements. Rating Concrete Bridges with No Plans A concrete bridge with unknown reinforcing details (no plans) can be rated for AASHTO Load (HS‐20) at the Operating Level, which is currently defined for load rating purposes as an HS‐20 design load, provided that the following two considerations are met:

• It has been carrying unrestricted traffic for many years.

• There are no signs of significant distress. Notation that the ratings are assumed must be inserted in the permanent Bridge Record described in Chapter 8, and the bridge should be inspected at more frequent intervals, usually each year, until an inspection history of at least four years is developed. This procedure is summarized in detail by Figure 5‐2. Three additional considerations for rating concrete bridges with unknown reinforcing are:

• Bridge must exhibit proper span‐to‐depth ratios of the main members, which indicates that the original design was by competent engineers. In general, this consideration means that for simple


span structures the span‐to‐depth ratio of main members should not exceed approximately 20. Span‐to‐depth ratios exceeding this ratio may indicate that the designer did not properly consider reasonable design truck loadings.

• Construction details, such as slab thickness and reinforcement cover over any exposed

reinforcing, should conform to specifications current at the time of the estimated construction date.

• Appearance should show that construction was done by a competent builder.

A comparative original design rating can be used to estimate the amount of reinforcing in the main members. Normally, if the design was done prior to about 1950 and the above five considerations exist, then the amount of reinforcing can be estimated based on a percentage of the gross concrete area of the main beams (if tee‐beam construction), or depth of slab (if slab construction). Two of the examples below describe this method, and a third example describes a method that can be used for pre‐stressed beam bridges with no plans or other documentation.

Figure 5‐2: Load Ratings for Concrete Bridges without Plans *Permit Trucks with gross or axle weights that exceed the state legal load limits will not be allowed to use these bridges. I.F. – Inspection Frequency. Refer to AASHTO Manual for Condition Evaluation of Bridges, Chapter 7, Section 7.4.


Examples of Rating Concrete Bridges with No Plans Example 1. A flat‐slab bridge designed between about 1930 and 1960 can be assumed to have approximately 0.7 percent tension steel based on the total slab depth. Calculations with this amount of steel using AS procedures with stresses, materials, covers, and live load distribution appropriate to the AASHTO Bridge Specifications for the estimated date of construction should give at or very near an H‐10, H‐15, or perhaps an H‐20 theoretical rating. Any other value would make the assumptions suspect. After this analysis is made, an analysis using LF procedures, HS loading, and current load distributions should give an acceptable rating. Flat‐slab bridges constructed off‐system can also often be rated by this procedure providing the above five considerations are also met. This method is not suitable for evaluation of FS slabs, which may be recognized as those with narrow roadways and tall integral curbs. Example 2. A multi‐beam concrete bridge built between about 1940 and 1965 can be estimated to have approximately 0.3 percent tension steel based on beam spacing and an estimated depth to the center of the steel group of 0.9 D where D is the total depth of the tee‐beam. As in Example 1, an “old” AS rating can first be calculated for comparison. If reasonable, then a modern LF rating can be made with HS loading and the estimated amount of reinforcing steel. The amount of steel can be adjusted slightly so the AS design exactly matches an H‐rating of H‐10, H‐15, or H‐20. Example 3. Some bridges are composed of pre‐stressed beams but no plans exist. This condition is often found for off‐system bridges. The ratings should be done using conservative assumptions and good engineering judgment. One procedure would be to assume that the beams were designed to an H‐15 loading in conformance with the estimated date of specifications. Using this assumption, an AS calculation can be made to estimate the even number of 12mm 114 T strands. An LF rating using the HS‐loading can then be performed based on this number and size of strand. In some countries, pre‐stressed beams were probably never designed to less than H‐15. Most beams have been designed to H‐20 or HS‐20. Pre‐stressed beam fabricators keep good records of their products, and identification of the design loading may sometimes be tracked down. All three of these examples should give H‐ratings using AS procedures that are close to a realistic design load. For instance, a calculated value of H‐14.4 could reasonably be assumed to verify that the original design was H‐15. A calculated AS value of H‐13 would be suspect , and further investigation will be required. Ratings for Unusual Bridges Unusual bridges, such as those composed of old railroad flat cars, can be rated, but care must be taken to ensure that the critical rating component is considered. For instance, flat cars were originally designed for a maximum point load combined with a uniform load over the whole car. When used for traffic loadings, even though the main two‐girder members may give a good equivalent HS load rating, the transverse stiffening members and floor beams often control the live load capacity. Another type of unusual bridge is the continuous cast‐in‐place (CIP) flat slab. Most of these bridges were designed in the 1940s and 1950s to an H‐15 or H‐20 load pattern. Unfortunately, the design negative moments were from the single truck load in one span. Current design procedures use a lane load with two concentrated loads in adjacent spans for the controlling negative moment case for longer continuous bridges or with two heavy axles of the HS‐20 load pattern at variable spacing in adjacent


spans for shorter continuous bridges. These bridges are thus under designed for HS‐loadings and as a consequence many should actually be load posted. However, the current AASHTO Bridge Specifications

(Ref 5‐2) do not differentiate between single‐and multiple‐lane distribution factors for slab bridges. As a result, this type of bridge has greater strength for multiple trucks positioned in the middle of the bridge span. Some structural evaluators will make live load distribution adjustments based on the number of lanes loaded for flat slab bridges. However, this must be done with care and properly correlated to two‐ or three‐dimensional methods of analysis. HS and HS Load Ratings Previously, all ratings were done with the equivalent H‐truck, shown in Figure 5‐1, or the HS‐truck shown in Figure 5‐1. Currently all ratings are only with the HS‐truck. A moment equivalency conversion from H‐ to HS‐ratings is not recommended since this process would assume that the structure was exactly designed for the given H‐loading. In addition, continuous spans cannot be converted by this process. Most structures have a degree of capacity past the design H‐load, particularly since load distribution assumptions of the AASHTO Bridge Specifications

have been made more liberal since the time many structures were commonly designed using H‐loads. However, as previously explained, some bridges were intentionally designed with AS methods to a 5 percent overstress for some components. It is not acceptable to ratio the design live load moments for an H‐truck to the same moment for an equivalent HS‐truck. For instance, if a 14.634 M simple‐span bridge has a design load of H‐15, the design load for moment equivalency would be HS‐10.8. However, due to the above reasons, the actual rating based on LF methods might easily be HS‐9 or HS‐13. A LF rating must be made.

13.4.5 Legal Loads and Load Posting Definition of Legal Loads Legal Loads are those that may safely use any of our highways and bridges. Some routes and many bridges must be load‐posted to protect them from possible damage. At this time, a load capacity of HS‐20 is considered to best represent the Legal Load for evaluation of the need for load posting. Truck loads are considered “legal” if the gross load, axle load, axle configuration, length, and width are within the current size and weight laws or rules. In general, the maximum gross load on any truck cannot exceed 36.40 T, the maximum load on any pair of tandem axles cannot exceed 15.50 T, and the maximum load on any single axle cannot exceed 9.10 T. Total length must not exceed 19.80 M and total width must not exceed 2.44 M. Legal Loads do not have a greater effect on bridges than the current HS‐20 design total gross load of 32.70 T even though they may have a total “legal” weight of 38.20 T. This apparent contradiction is due to the different axle load configurations and numbers of axles. Load Posting Load posting is often required for structures that, due to their original design or condition, do not have the structural capacity to safely carry the Legal Loads. Posting may be at Operating Rating levels


provided that the Condition Ratings exceed those defined in Figure 5‐3 and Figure 5‐4 and other requirements are met. Otherwise, if the Condition Ratings are less than those defined, the Posting must be at Inventory Rating levels. All load postings of a given truck size actually mean that two trucks of the posted capacity can safely pass on the bridge. This concept is often misinterpreted by those doing load ratings and making load posting recommendations. It is recognized that a bridge posted for an HS‐5 (8.20 T gross load) can safely carry a single truck of significantly more than 8.20 T. No method ensures that only a single truck is on the bridge. Therefore, assume that two trucks of the same size could be passing on the bridge simultaneously. However, some bridges, particularly off‐system, are load posted assuming only one rating truck even though they may be wider than 5.50 M. This condition usually occurs due to the volume of truck traffic, structure width or approach roadway width, striping, runners, etc. making them functionally one‐lane bridges for trucks. It is important to recognize that even though a bridge may have been designed to an H‐15 loading, it may not need to be load posted due to considerations discussed previously, such as reinforcement or member size in excess of the theoretical amount, more liberal load distribution now used in analysis, and LF analysis methods which usually increase Inventory Ratings significantly more than the original design loading. The recommended load posting of all off‐system bridges must be supplied to the affected localities. HIB will provide the necessary posting signs and placement hardware. Typical load posting signs are shown in Figure 5‐5.


Figure 5‐3: On‐System Load Posting Guidelines Permit Loads will not be allowed on bridges that are load posted.

• If the bridge has not been rehabilitated or replaced in 24 months then the structure shall be closed.

I.F. – Inspection Frequency. OR – Operating Rating (Item 64) IR – Inventory Rating (Item 66)


Figure 5‐4: Off‐ System Load Posting Guidelines

• Permit Loads will not be allowed on bridges that are load posted If the bridge has not been rehabilitated or replaced in 24 months then the structure shall be closed. I.F. – Inspection Frequency OR – Operating Rating (Item 64) IR – Inventory Rating (Item 66)


Figure 5‐5: Typical Load Posting Signs


Procedures for Changing On‐System Bridge Load Posting

The following table outlines the procedure for changing the load posting of an on‐system bridge.

Changing Load Posting of an On‐ System BridgeStep Responsible Action

Party1 Inspection Complete "Recommend change in Bridge Load Zoning" Form,Makes a request

Contractor that involves a new l imit or a reduction of a current load l imit, attach the mostrecent inspection report, plans (lay‐outs and structura l deta i ls ), and any load ratings that support the recommended change

2 RBD Review the request and supporting documents , and i f review supports therecommended change i s sues an instruction order.

3 Inspection Noti fy the the Traffic Authori ties of any va l id load restriction orderContractor

4 Traffic Wil l erect s igns indicating proper load l imi tAuthori ties

5 Inspection Wi l l veri fy i f the proper load l imit has been erected and record the date of Contractor erection

Under the following conditions, Inspection Branch should submit a completed Form showing reasons for restriction removal.

• Repair or rehabilitation of a bridge that increases load capacity and eliminates a load restriction.

• Construction of a new bridge that replaces one with a load restriction. Procedures for Emergency On‐System Bridge Load Posting The following table outlines the procedure for changing the load posting of an on‐system bridge in an emergency.

Changing Load Posting of an On‐ System BridgeStep Responsible Action

Party1 Inspection Noti fy the RBD that an emergency load restriction i s required.

Contractor Identi fy deficiencies that jus ti fy the placement of an emergency load l imi t2 Inspection Determine the load l imit, i f requi red and verba l ly authorize an emergency load

Contractor restriction for a period not to exceed 60 days i f necessary3 RBD Issues an order authorizing temporary load l imits and speci fying the duration

of the temporary l imit4 Inspection Noti fy the the Traffic Authori ties of any bridge load restriction

Contractor5 Traffic Authori ties Wi l l erect s igns immediately indicating emergency load l imit

If the emergency load limit is required for a period longer than 60 days, Inspection contractor should submit a request to the RBD for the emergency load restriction to remain in place for another 60 days. If the bridge is not replaced or repaired before the emergency load restriction extension expires, the Inspection Contractor should submit a request to the RBD for a permanent load restriction following the procedure for changing on‐system bridge load postings.


Closure of Weak Bridges Bridges with less than an HS‐3 Operating Rating capacity must be closed. These policies must be followed for on‐system bridges and are strongly recommended for the municipalities with jurisdiction over off‐system bridges. Bridges with Inventory Ratings less than HS‐3 but with Operating Ratings greater than HS‐3 may remain open for a limited amount of time. If it is desired to leave a bridge in this category open, then the inspection frequency must not exceed six months and the bridge must be categorized for Priority 1 rehabilitation or replacement. If after 24 months the bridge has not been rehabilitated or replaced, then it should be closed. Off‐System Bridge Closure Procedures If inspection reveals deterioration that affects an off‐system bridge’s ability to safely carry vehicular traffic, the department may use the following procedure to recommend that it be closed for safety reasons:

Recommending Off‐ System Bridge ClosuresStep Responsible Action

Party1 Inspection Wi l l immediately noti fy the RBD i f i t determines that a bridge should be

Contractor closed based on the resul ts of inspection they conducted.2 RBD They wil l veri fy as soon as poss ible the condi tion of a bridge recommended

for closure by Inspection Contractor.3 RBD Wil l immediately noti fy the the Traffic Authori ties of a va l id closure

recommendation.4 Traffic Wil l close the bridge and noti fy the RBD when the bridge i s closed to

Authori ties traffic.5 Inspection Wi l l veri fy closure of the bridge when i t receives noti fication and wil l include

Contractor a photo or certi fied documentation veri fying closure in the bridge inspection fi le and wil l prompt update the Bridge Inspection database to reflect the closure s tatus of the bridge. (See Item 41 in the coding _guide)

6 Inspection If the bridge wil l reman closed for an extended period of time, they wil l veri fy Contractor and document with a photo that the bridge i s sti l l closed to traffic as part of

the regular inspection cycle.

13.5 Routing and Permits

13.5.1 Overview

This Chapter includes discussion of the following topics:

• Role of the Bridge Inspection Engineers, and the Traffic Authorities

• Permits

• Example Comparison of Inventory, Operating, and Permit Loads


13.5.2 Role of Inspection Engineers and the Traffic Authorities One of the responsibilities of the Bridge Inspection Engineer is to assist the Traffic Authorities in the evaluation of over‐height and over‐width permit routes based on experience. The current electronic Bridge Inventory Files are expected to be accurate; however, should the values for clearances in the Bridge Inventory Files appear suspect, the actual plans should be reviewed and/or a field visit made prior to issuing a permit. The Traffic Authorities issues the permit only after review by the RBD. A supplementary role of the Bridge Inspection Engineer is to notify the Traffic Authorities of any changes to bridge load postings, particularly for bridges which have never been previously posted. The Traffic Authorities shall maintain a master set of maps showing the various width, height, and load restrictions on all highways. All permits are issued by the Traffic Authorities with the cooperation of the RBD. For overweight permits, the Traffic Authorities also works closely with the RBD. Any super‐heavy permits must also be coordinated the RBD for structural evaluation of the bridges on a proposed route. This process is fully explained below. The Traffic Authorities, in conjunction with the owner‐mover, selects a preliminary route based on known information in the Bridge Inventory Files, day‐to‐day construction status, road closures, and other known route restrictions.

13.5.3 Permits Overheight and Overwidth Permits Many permits for over‐height or over‐width loads. The routing of these loads usually depends on data contained in the electronic Bridge Inventory File. These types of loads do not normally require a structural evaluation of the affected bridge unless the weight and axle load distribution is such the overweight permit may also be required. The electronic Bridge Inventory file gives the values fro available clearances as Items 51 (Roadway Width), 52 (Deck Width), 53 (Vertical Clearance Over Roadway), 54.2 (Vertical Clearance Under Bridge), 55 (Lateral Under‐clearance on Right), and 56 (Lateral Under‐clearance on Left). These items taken together usually give sufficient information to define the limits for the passage of over‐height and over‐width vehicles. The Bridge Inspector can quickly access the electronic Bridge Inventory file to determine if the proposed route is capable of handling the proposed over‐width or over‐height load. Truss bridges are particularly of concern for both these types of loads since many are in the 5.5 M – 6.5 M width range, and vertical clearance to the portals is often less than normal current design clearances. The electronic Bridge Inventory file gives vertical clearances to the least millimeters of clearance over the roadway, including shoulders rounded down to the nearest millimeter. The posted clearance signs are normally 76.3 mm less than this value. The clearance symbols maintained on the Traffic Authorities permit maps are rounded down to the next 150 mm below the posted clearance. For instance, if the actual recorded clearance is 4320 mm, the clearance sign is 4240 mm, and the permit maps show the


maximum available clearance as 4110 mm. Occasional over‐height loads can therefore be permitted for heights slightly over the limits given in the Traffic Authority permit maps provided there is close coordination between the RBD and the owner‐mover with pre‐move specific measurements taken. Normally, over‐width permits are granted simply on the basis of available Roadway Width (the clear distance between curbs or railings). If the over‐width load is configured such that the load will adequately clear bridge railings, then moves may be granted for loads significantly wider than the Deck Width with the careful cooperation of all concerned parties including escort vehicles and traffic control. Damage and or removal of signs and delineators may occur for some over‐width permits. RBD personnel should ensure that all such temporary changes be corrected immediately after the permit load has passed. Overweight Permit Loads Misconceptions often arise about the relationship between Operating Ratings and Overweight Permit Loads. The primary difference is that Overweight Permit Load analysis usually assumes only one load on the bridge, which therefore allows the use of single‐lane load distribution. The Operating Rating is based on the standard AASHTO load distribution given in the current Standard Specifications for Highway Bridges for multi‐lane distribution for bridges over 5.50 M in width. This distribution implies two or more of the Operating Rating trucks being on the bridge side‐by‐side at the same time. The other major difference is that Operating Ratings and Overweight Permit Loads use different load multipliers, resulting in permit load analysis being significantly more liberal than Operating Rating analysis. The current Operating and Inventory Ratings, the age and type of structure, the span lengths, and the Condition Ratings are reviewed for any structure proposed on a permit route. Any Condition Rating of 4 or less acts as a flag to the permit route reviewer who will then request more detailed information on the structure, including the written inspection comments. Reduced strength in a portion of a bridge can often be avoided by controlling the load path of the Overweight Permit Load across the bridge. Superheavy Loads Overweight Permit Loads are classified as “routine” or “super‐heavy.” Routine Overweight Permit Loads may be allowed in the regular traffic stream, sometimes with escorts if the load is also over‐length or over‐width. Therefore, the standard AASHTO load distributions are appropriate since there may be a legal truck alongside the routine permit truck crossing a bridge at the same time. The term Super‐heavy Permit Load usually designates total loads over 115.6 T gross to represent the lower range of a typical super‐heavy load and consists of a 6.5 T steering axle followed by four groups of three axles, each totaling 27.3 T. Any configuration with multiple axles with a gross load of over 115.6 T is considered a super‐heavy load and requires structural evaluation of individual bridges. Loads with individual axles or axle group weights that exceed the maximum permit weights are also considered to be super‐heavy. Any load exceeding 91.0 T with a total overall length of less than 29.0 M is also considered super‐heavy. The Super‐heavy Permit often requires that the load cross all bridges straddling a lane line in the case of four or more lanes on a two‐way bridge, or straddling the center line for a two‐lane bridge. This


procedure ensures that other legal trucks will not be alongside the super‐heavy load and also gives better load distribution. The AASHTO load distributions used for super‐heavy loads are therefore usually single lane, thus allowing higher Super‐heavy Permit gross loads to safely cross the bridge. A printout of the proposed list of bridges to be crossed is reviewed by the Traffic Authorities and the RBD. Often, based on experience of the evaluator and other guidelines, it is necessary to structurally evaluate only a fraction of the bridges on an extensive proposed super‐heavy route. Any bridges on the route which have Deck Condition Rating or Superstructure or Substructure Component Ratings of 4 or less trigger the need for review of the actual written Bridge Inspection Record. This bridge‐by‐bridge evaluation is one of the primary reasons that the data in the electronic Bridge Inventory Files must be accurate and up‐to‐date. Super‐heavy Permit Loads are usually speed‐controlled on bridges, sometimes as slow as a walk speed to minimize impact forces. Many Super‐heavy Permit Loads also have greater than the usual 1.83‐ M axle gage. The gages for Super‐heavy Permits can commonly be as much as 6.10 M with 16 tires on each axle line. Methods of load distribution for these special carriers cannot directly use the customary AASHTO distributions, which are based on 1.83‐ M axle gages with four tires on an axle line. Other Differences Between Overweight Permits and Operating Rating There are other major difference between Operating Ratings and Overweight Permit Loads. The Operating Rating is usually based on Load Factor (LF) criteria, which use multipliers of 1.3 applied to both the dead and live loads. The live load has an additional allowance of up to 30 percent for impact. Note that Inventory Rating uses a significantly higher live load multiplier of 2.17. The result for either Operating Rating or Inventory Rating is compared to the yield or ultimate strength capacity of the members. A “phi” strength reduction factor (usually from 1.0 to 0.85) is also applied for concrete members. Overweight Permit Load analysis usually assumes a factor of 1.0 applied to both the dead and live loads. Ten to 30 percent is added to the live load for impact, depending on the speed control and type of load suspension system. Stresses are compared to an allowable maximum of 75 percent of the yield capacity of steel members or 75 percent of the ultimate capacity for concrete members. The reciprocal of 75 percent is 1.33; thus it can be seen that Overweight Permit Load analysis with AS methods has essentially the same factor of safety as an analysis using LF criteria. This result will be demonstrated below by a specific example comparison. Overloads on Posted or Substandard Bridges Occasionally a request is made for a Routine Overweight Permit or a Super‐heavy Overweight Permit to cross a load‐posted bridge. Traffic Authorities does not allow overweight permits for posted bridges. However RBD can allow overweight vehicles to cross load‐posted bridges only when there is no other route. For these cases, RBD qualified Contractors perform structural evaluation of the bridge(s) in close coordination with the mover of the load. The evaluations may consider the use of shimmed mats,


temporary shoring, or specialized moving equipment that allows redistribution of the load between axle groups as the load crosses. Certain other bridges that are not load posted may not be capable of carrying Routine Overweight Permit Loads or Super‐heavy Permit Loads. Bridges that are in this category include, but are not limited to, continuous flat slabs with original H‐15 designs. These bridges have short spans and were designed with the single H‐load pattern truck placed along the span for maximum design conditions. Many of these bridges when rated with the now required HS‐load pattern, and even using LF analysis, will rate at significantly less capacity than other types of bridges designed with H‐load patterns. These bridges, though not currently load posted, must be carefully evaluated when overload permits are considered. This is the primary reason that the original design loads given in the electronic Bridge Inventory Files should be entered correctly. Often these bridges have been widened, and the widening design load has been incorrectly entered as the original design load. Pre and Post Move Inspection Another occasional responsibility of the Bridge Inspection Supervisor/ Engineer is to inspect bridges before and after the passage of a particular overweight permit load. A representative of the owner‐mover should be present at these types of inspections. Cast‐in‐place short span slab bridges, particularly those which have been widened from an original H‐10 design to an H‐15 or H‐20 design, are susceptible to cracking by overloads. Unusual bridges, such as arch spans, segmentally constructed post‐tensioned spans, or long‐span plate girder bridges, may also need special attention before, during, and after the move of an overweight permit load. It has been found that simple attention to the sounds made by a bridge when the load passes will call attention to possible broken diaphragm connections or lateral wind bracing connections that actually act as torsional bracing for curved and/or heavily skewed structures.

13.5.4 Example of Inventory, Operating, and Permit Loads Typical Continuous I‐Beam Bridge To further demonstrate the differences between the various types of analyses, a typical standard bridge is chosen for comparative analysis. This bridge is a three‐span continuous I‐Beam bridge originally designed in the 1950s and 1960s . These Bridges were commonly designed to H‐15 loads (13.6 Tons). This bridge has a 7.90 M. roadway between faces of railings and is composed of four 762 mm deep wide‐flange rolled beams with relatively short cover plates at the interior supports. The beams are spaced at 2240 mm, and the slab is 1650mm. An elevation and cross‐section of the bridge are shown in Figure 6‐1. The design is non‐composite, meaning that the slab is assumed to slip longitudinally along the top flanges when loaded. The beams are 36W135 continuous with 254 mm. x15.875 mm x 4268 mm cover plates top and bottom at supports


Figure 6‐1: Typical I‐Beam Bridge Elevation and Cross‐Section Rating Analysis Steps The steps used in the typical rating analysis for the structure are describes below. Calculate Dead Load. Using the total steel weight given in the plans, subtract calculated weight of beams including cover plates and check that remainder is about 5 percent of beam weight. This result represents the diaphragms, connections, and other miscellaneous steel. If this number is not about 5 percent, determine the discrepancy. Sometimes the total weight in the plans is in error, but this check usually gives the rater a verification for the estimated dead load. Use the total steel weight, which includes the diaphragms, as a uniform load per LF, distributed equally to one of the interior beams. Use


the total slab quantity given in the plans calculated as a uniform load per LF also distributed equally to an interior beam. Verify by comparison to the dead load of slab for a typical interior beam using the slab thickness. Add in dead load for any overlay and railings. Compute Dead Load Moments. Dead load moments need only be calculated at critical locations such as the maximum positive moments for each span and the negative moments at the interior supports. The analysis should use the actual span lengths center‐to‐center of bearing, and not the nominal span lengths. It is preferable to use a computer program, but hand analysis from continuous beam coefficients is also acceptable. The normal sizes of cover plates over supports will “draw” up to about 6 to 12 percent more negative moment, and will reduce positive moments when compared to a constant cross section analysis, which is assumed when using continuous beam coefficients or other similar tables or charts. Almost all continuous beam designs used influence coefficients for a constant cross section. Determine Controlling Live Loading Conditions. Some computer programs do this determination automatically, but there is risk in using these programs unless the user is familiar with their limitations and assumptions. One popular program is BMCOL51, which is a continuous beam analysis program. It allows any pattern of live load to be moved in increments along the beam, which can have cover plates and any areas of composite section if necessary. Thus it is particularly suited to the analysis of super‐heavy loads. It can also identify the locations where the concentrated load(s) for lane loads must also be placed. Most continuous beams will have the following live load maximum moments:

• Max positive moment in end and center spans will usually be from an HS‐20 live load with 4.20 M center‐to‐center of trailer axles. However, for very long plate girders, the lane loading criteria may sometimes control positive moment.

• Max negative moment will also usually be from the HS pattern, perhaps with more than 4.20M

between the trailer axles if total length of first plus second spans is less than about 21.30 M. If the sum of the first two spans is more than about 22.90 M or 24.40 M, then the negative moment will be from lane loading of the two adjacent spans with the concentrated loads applied at the critical positions in the two spans.

Calculate the Moments and Load Ratings. Apply the appropriate load factors for the various ratings to both the dead and live load moments at each member location being investigated. Subtract the dead load effect from the member capacity at yield (if load factor analysis) or from the member capacity at allowable stress (if allowable stress analysis). The remainder is the live load capacity. Ratio the remainder to the calculated live load value at the location and multiply by the live load ton designation. The result is the member rating at that location. It is best to understand this basic process rather than use a set formula for calculating the load rating. Tabulate the Maximums. Identify the locations for which stresses and ratings are to be calculated. Often the maximum positive moment sum of dead plus live effects will not be at the point of maximum dead load or live load moment. This condition is another reason to use a computer analysis such as BMCOL51. This program allows the combination of dead and live loads to be investigated at all points along the continuous member with proper consideration of the effects of cover plates and composite regions, if


any. The maximum moments in the end spans may not be the same, even though they have the same span length, due to the unsymmetrical live load pattern. For the results discussed in the remainder of this section, Program BMCOL51 was used with 21.00– 25.14 – 21.00 M spans. Results for I‐Beam Bridge An H‐pattern was used for comparison (normally not necessary) with no railing and no overlay as an additional check on the original design using allowable stresses. This design pre‐dated the 1965 design shown on the standard plans and obviously was done using an allowable stress of 124 MPa. In 1965 many standard details were changed to specify “H.Y.C.” structural steel which is equivalent to ASTM A‐36. However, the design load was kept the same, and no change was made in the size of the cover plates. An HS loading, using the allowable stress or load factor methods, and Inventory Rating or Operating Rating methods was also made for comparison. The various analyses are summarized in the following table:

Table 6.1 Comparison of Analyses for Example Bridge Loading Analys is Method 1st or 3rd Span Support Middle Span

H (1) N AS ‐IR H 20.08 H 14.24* H 18.94

H (2) N AS ‐IR H 23.46 H 17.59* H 22.28

HS (3) N AS ‐IR HS 15.78 HS 17.60 HS 14.84*

HS (4) Y AS ‐IR HS 12.65 HS 10.40* HS 11.48

HS (5) Y LF ‐ IR HS 15.84 HS 17.80 HS 14.97*

HS (6) Y LF ‐OR HS 26.40 HS 29.67 HS 24.96

N = Light Rai l ing and no overlay Y=T501R ra i l ing and 2‐in overlay

AS=Al lowable Stress LF= Load Factor ,

OR=Operating Rating IR = Inventory Rating

*= Control l ing Rating Discussion of the Analysis Comparisons The various analyses summarized in Table 6.1 are discussed in the sequence of the loading number. Current bridge rating analysis usually requires only loadings HS (5) and HS (6). However, if the resulting rating is significantly different than the design load, then solutions similar to loadings H (1) or H (2) may be necessary to determine the reasons for the difference. H (1) ‐ Used to verify analysis with an assumed allowable stress of 124.02 MPa which is appropriate for

A7 steel. Also assumed to have no overlay and light railings. Note that the controlling rating of H14.24 is close to H‐15. There would be an overstress of 2.5 percent if exactly H‐15 loading was used. Designing up to a 5‐percent overstress was very common for these structures.

H (2) ‐ This comparison analysis was made with an allowable stress of 137.80 MPa, which is

appropriate for A36 steel. The remainder of the following comparisons are also with A36 steel. HS (3) ‐ This comparison is with an HS truck. Note that the controlling HS14.84 rating implies a total

Individual rating truck load of 26.7 T, which compares with the H17.6 rating truck of 17.6 T.


HS (4) ‐ This analysis demonstrates the effect of using the actual current in‐place modern railing, a T501R retrofit railing in this case, and a 50 mm overlay. This amount of overlay is very common for structures of this age. Note that the controlling rating shifts from the end span to the support due to the added influence of the greater uniform dead load. The reduction in the rating is 30 percent simply due to the added dead load.

HS (5) ‐ This analysis demonstrates the current IR for the bridge using LF analysis methods. The HS14.97

rating implies a single inventory rating truck load totaling 27 T or two trucks side‐by‐side totaling 54 T.

HS (6) ‐ This analysis demonstrates the current OR for the bridge using LF analysis methods. The HS24.96

rating implies a single operating rating truck load totaling 45 T or two trucks side‐by‐side totaling 90 T.

Note that the OR of solution HS (6) is equal to 5/3 x the IR of solution HS (5) which directly reflects the difference in the live load rating factors. 13.6 Bridge Programming

13.6.1 Basis for Bridge Rehabilitation or Replacement A bridge is considered to be Structurally Deficient if it is not able to carry the truck loads expected of the bridge. The highway or road system on which the bridge is located affects the expected truck loading. For instance, a bridge on the Interstate highway system must be considered able to have an Inventory Rating of at least HS‐20, while a bridge on an off‐system county road would be considered adequate to carry its necessary truck loads if the Inventory Rating was HS‐15. A bridge is considered to be Functionally Obsolete if the deck width, vertical clearance, waterway adequacy, or approach roadway alignment are not adequate for the traffic type, traffic volume, or expected flood waters.

13.6.2 Bridge Program Qualification for Rehabilitation or Replacement HIB projects are selected using a prioritization process that calculates a score for each candidate bridge project. The score considers Average Daily Traffic (ADT), cost per vehicle, bridge condition, roadway width, and the bridge Sufficiency Rating. The scoring process is referred to as the Eligible Bridge Selection System (EBSS). The selection of bridges is made yearly in the order of descending TEBSS scores for the on‐ and off‐system eligible bridges. However, bridges with one or more critical deficiencies may also be selected, regardless of EBSS score. Such critical deficiencies are defined as extremely low Condition Ratings, Sufficiency Ratings, or load capacities. For instance, bridges which are closed, or that have a Deck Condition plus Superstructure Condition Rating of 10 or less, automatically qualify. Bridges that have Sufficiency Ratings less than 30 also automatically qualify.


Eligible Bridge Selection System (EBSS) The Sufficiency Rating, established during the biennial bridge inspections, plays an important role in selecting which of the bridges are eligible for rehabilitation or replacement. In order for a bridge to be considered eligible, it must have a Sufficiency Rating of 80 or less and be either Structurally Deficient or Functionally Obsolete. These three terms are defined in following subsections with the same titles. If the Sufficiency Rating is below 50, the bridge is eligible for replacement or rehabilitation if the anticipated replacement costs are greater than 120 percent of the rehabilitation costs. Rehabilitation may be considered if the Sufficiency Rating is between 50 and 80. Bridges cannot be considered eligible if their Sufficiency Rating is greater than 80. Structural Deficiency A bridge is considered Structurally Deficient if there is a Condition Rating of 4 or less for:

• Item 58 (Roadway) or

• Item 59 (Superstructure) or

• Item 60 (Substructure)

• or if there is an Appraisal Rating of 2 or less for:

• Item 67 (Structural Condition) or

• Item 71 (Waterway Adequacy)

• Item 71 is considered only if the last digit of Item 42 (Type of Service Under the Bridge) is 0, 5, 6, 7, 8, or 9

Functional Obsolescence Three methods establish if a bridge is Functionally Obsolete: An Appraisal Rating of 3 or less for Item 68 (Roadway Geometry), and Item 51 (Bridge Roadway Width) is less than the following:

5000

Item 51 (Roadway Width)

Curb to Curb (feet)

Item 29 (ADT)

equal to less than

250

750

2700

20

22

24

30 ADT greater than 35,000 requires review by HIB Bridge Division


An Appraisal Rating of 3 or less for either of:

• Item 69 (under‐clearances) or

• Item 72 (Approach Roadway Alignment)

Item 69 is considered only if the last digit of Item 42 (Type of Service Under the Bridge) is 0, 1, 2, 4, 6, 7, & 8 An Appraisal Rating of 3 or less for either of:

• Item 67 ( Structural Condition) or

• Item 71 ( Waterway Adequacy)

13.6.3 Sufficiency Ratings Calculation of Sufficiency Ratings The Sufficiency Rating of a bridge is determined during the biennial bridge inspection and is intended to indicate a measure of the ability of a bridge to remain in service. Calculations for Sufficiency Ratings utilize a formula that includes various factors determined during the bridge field inspection and evaluation. The items considered below are those described in the instructions for coding guide. Ratings are on a scale of 1 to 100, with 100 considered as an entirely sufficient bridge, usually new; an entirely deficient bridge would receive a rating of 0. Only bridges that carry vehicular traffic receive a Sufficiency Rating. An interactive program can be used to calculate Sufficiency Ratings and determine Structural Deficiency and Functional Obsolescence. One of those programs is called BRISUF and it calculates the Sufficiency Rating based on data entered through an interactive prompt process Whether using the prompted program BRISUF or hand calculations, the Sufficiency Rating (SR) is calculated by the equation: SR = S1 + S2 + S3 ‐ S4 A discussion of how to arrive at each variable immediately follows. S1 is the Structural Adequacy and Safety (55 maximum, 0 minimum) calculated by the equation: S1 = 55 ‐ ( A + I ) A is the Reduction for Deterioration (not to exceed 55 or be less than 0) based on the lowest value of Item 59 (Superstructure Rating) or lowest value of Item 60 (Substructure Rating):

if ≤ 2 then A = 55


if = 3 then A = 40 if = 4 then A = 25 if = 5 then A = 10 if ≥ 6 then A = 0 if = N then A = 0

I is the Reduction for Load Capacity (not to exceed 55 or be less than 0) calculated by the following equation and table: I= 0.2778 ( 36 ‐ AIT ) AIT is the Adjusted Inventory Tonnage, calculated by the following table of multipliers based on Item 66 (Inventory Rating):

1st digi t of AIT=2nd & 3rd digi ts

Item 66 i s… of Item 66

multipl ied by …..

1 1.56

2 1.00

3 1.56

4 1.00

5 1.21

6 1.21

9 1.00 S2 is the Serviceability and Functional Obsolescence (30 maximum, 0 minimum) calculated by the equation: S2 = 30 ‐[J + ( G + H ) + I ] J is a Rating Reduction (not to exceed 15) calculated by the following equation and tables: J = A + B + C + D + E + F

If Item 58 If Item 67 (Deck Condition) (Structural Evaluation) ≤ 3 A = 5 ≤ 3 B = 4 = 4 A = 3 = 4 B = 2 = 5 A = 1 = 5 B = 1 ≥ 6 A = 0 ≥ 6 B = 0 = N A = 0 = N B = 0

If Item 68 If Item 69


(Deck Geometry) (Under‐clearances) ≤ 3 C = 4 ≤ 3 D = 4 = 4 C = 2 = 4 D = 2 = 5 C = 1 = 5 D = 1 ≥ 6 C = 0 ≥ 6 D = 0 = N C = 0 = N D = 0

If Item 71 If Item 72 (Waterway Adequacy) (Approach Roadway Alignment)

≤ 3 E = 4 ≤ 3 F = 4 = 4 E = 2 = 4 F = 2 = 5 E = 1 = 5 F = 1 ≥ 6 E = 0 ≥ 6 F = 0 = N E = 0 = N F = 0

(G + H ) is a Width of Roadway Insufficiency (not to exceed 15) calculated by the following relationships. The values for X and Y are first found by the following two equations: X (ADT/Lane) = Item 29 (ADT) ÷ First two digits of Item 28 (Lanes) Y (Width/Lane) = Item 51 (Roadway Width) ÷ First two digits of Item 28 (Lanes) Use following three conditions of (1), (2), or (3) to then obtain the values for G and H :

1. For all bridges except culverts : (Item 43.4, Culvert Type, must be blank or 0) If Item 51 (Roadway Width) + 2 feet is less than Item 32 (Approach Roadway Width), set G = 5 If Item 51 (Roadway Width) + 2 feet is greater than or equal to Item 32 (Approach Roadway Width), set G = 0

2. For one‐lane bridges (including one‐lane culverts):

If the first two digits of Item 28 (Lanes) = 01, and Y < 14 set H = 15

14 ≤ Y < 18 set H = 3.75 ( 18 ‐ Y )

Y ≥ 18 set H = 0

3. For bridges with two or more lanes (including culverts):

If 1st two digits of Item 28 = 02 and Y ≥ 16, set H = 0




If any one of the above four conditions is met, do not continue with further determination of H since no lane width reductions are necessary.

Otherwise, determine H based on the following values for X (ADT/Lane) and Y (Width/Lane):


If and set

X ≤ 50 Y < 9 H = 7.5 Y ≥ 9 H = 0

50 < X ≤ 125 Y < 10 H = 15

10 ≤ Y < 13 H = 5.0 (13 − Y) Y ≥ 13 H = 0

125 < X ≤ 375 Y < 11 H = 15

11 ≤ Y < 14 H = 5.0 (14 − Y) Y ≥ 14 H = 0

375 < X ≤ 1350 Y < 12 H = 15

12 ≤ Y < 16 H = 3.75 (16 − Y) Y ≥ 16 H = 0

X > 1350 Y < 15 H = 15

15 ≤ Y < 16 H = 15.0 (16 − Y) Y ≥ 16 H = 0

Note that in any case, the value of (G + H ) cannot exceed 15.

I is a Vertical Clearance Insufficiency (not to exceed 2) set by the following: If Item 100 (Strategic Highway Corridor Network, also called STRAHNET) is greater than 0 and Item 53 (Min Vert Clearance over deck) ≥ 1600 set I = 0 Item 53 (Min Vert Clearance over deck) < 1600 set I = 2 If Item 100 (STRAHNET) is equal to 0 and Item 53 (Min Vert Clearance over deck) ≥ 1400 set I = 0 Item 53 (Min Vert Clearance over deck) < 1400 set I = 2 S3 is the Essentiality for Public Use (not to exceed 15) calculated by the equation: S3 = 15 ‐ ( P + M ) P is the portion for Public Use (not to exceed 15) First calculate K which is a value based on the previously calculated S1 and S2 : K = ( S1 + S2 ) ÷ 85 P = (Item 29 (ADT) × Item 19 (Detour Length) × 15) ÷ (200,000 × K) M is the portion for Military Use (not to exceed 2) If Item 100 (Strategic Highway Corridor Network, also called STRAHNET) is greater than 0, set M = 2 If Item 100 (STRAHNET) is equal to 0, set M = 0 Note that in any case, the value of ( P + M ) cannot exceed 15. S4 is a Special Reduction which is used only when S1 + S2 + S3 is greater than or equal to 50. S4 is calculated by the following equation: S4 = R + S + T


R is a Detour Length Reduction (5 maximum, 0 minimum) R = [ Item 19 (Detour Length) ]4 x [ 5.205 X 10‐8 ] S is a Structure Type Reduction set by the following: If the 1st digit of Item 43.1 (Main Span Type) is 7 or 8 (Movable, Suspension, or Stayed), or if the 2nd digit of Item 43.1 is 2, 3, 4, 5, 6, or 7 (portion of structure is beside or above roadway), set S = 5 Otherwise, set S = 0 T is a Traffic Safety Feature Reduction set by Item 36 (Traffic Safety Features) which rates the adequacy of the bridge railings, transitions, and approach guard fences: If 1 or none of the 4 digits of Item 36 are 0, set T = 0 If 2 of the 4 digits of Item 36 are 0, set T = 1 If 3 or the 4 digits of Item 36 are 0, set T = 2 If all 4 of the digits of Item 36 are 0, set T = 3

13.7 Bridge Records

13.7.1 Overview Summary This presents the specific requirements for inspection records for Libyan bridges. Records must be prepared and kept in a consistent manner, whether done by RBD personnel or by Contractors. This chapter includes discussion of the following major topics:

• Definition of Terms

• Contractors Requirements

• Coding Guidelines

• Forms

• Calculations

• Data Submittal

• Bridge Folder


13.7.2 Definition of Terms Bridge Record Terms A partial list of definitions related to bridge inspection is provided in various chapters of this Manual. The following discussion of Bridge Records includes some specific terms: Bridge. A structure, including supports, erected over a depression or an obstruction, such as water, a highway, or a railway; having a roadway or track for carrying traffic or other moving loads; and having an opening measured along the center of the roadway of more than 6M between faces of abutments, spring lines of arches, or extreme ends of the openings for multiple box culverts or multiple pipes that are 1.50M or more in diameter and that have a clear distance between openings of less than half of the smallest pipe diameter. Bridge Folder. The file for each bridge maintained by the District Bridge Inspection Coordinator. The Bridge Folder has dividers on which the various bridge record documents can be fastened in a specific order. Bridge Identification. The unique 12‐digit number assigned to any structure meeting the definition of a bridge. The number includes the 3‐digit Shabiya Number, the 4‐digit Control Number, the 2‐digit Section Number, and the 3‐digit Permanent Structure Number. The Planning Department assigns the road and city street index numbers, which begin with a letter instead of number. This off‐system index number uses the same 6 digits assigned to Control and Section for on‐system highways. The Permanent Structure Number for off‐system bridges is assigned by the district. Bridge Inventory File. This consists of electronic data of RBD’s bridge inventory, inspection, and appraisal files for each bridge on a public roadway in Libya. The data can be entered from a completed coding form or can be are entered directly from an input screen of any appropriate data entry device. The instructions for coding guide describe the step‐by‐step data entry requirements. Bridge Record. The over‐all collection of data including the Bridge Folder with completed forms, printout of coded electronic data, sketches, cross sections, photos, etc. It also includes the Bridge Inventory File stored on electronic media. The Bridge Record also includes the bridge plans, if available, copies of which should be in the Bridge Folder. Some of the bridge plans may also be available on electronic media in the form of computer‐aided drafting (CAD) drawings.


Culverts. Multiple‐barrel box culverts or multiple‐pipe culverts are sometimes classed as bridges and a complete Bridge Record is made. The 1994 AASHTO Manual defines a bridge as any structure carrying traffic (highway or railroad) having an opening measured along the centerline of the roadway of more than 6.0 M between the limits of the extreme openings of abutments, arches, or multiple boxes. This definition has created the anomaly in some cases where, for instance, three 1.80 M multiple box culverts installed at more than about a 15‐degree skew to the roadway must have a Bridge Record. If the same three box culverts are installed perpendicular to the roadway, they have no Bridge Record. The AASHTO definition continues for multiple‐pipe culverts by stating that they may be classed as bridges provided the distance between individual pipes (the fill) is less than half the adjacent pipe diameter. To facilitate consistency in future recording of culvert installations, a separate subsection titled Multiple‐Pipe Culverts is contained in this chapter. Elements Data. The supplemental electronic bridge inventory, inspection, and appraisal data taken for RBD, the data are entered on forms, but entry from a prompt screen of an appropriate data entry device can also be used. The Elements: Field Inspection and Coding Manual describes the step‐by‐step data entry requirements. Engineer. The Professional Engineer having responsibility for ensuring the accuracy of the information contained in the Bridge Record. A pre‐qualified Contractor that has a Consulting Engineer on board engaged by HIB to perform routine bridge inspections is also considered in the following discussions to be covered by the term Engineer. The same basic procedures are used by RBD personnel as are required for Contractors. Forms. Specific forms such as Bridge Inspection Record Form, Bridge Appraisal Worksheet Form , Bridge Inventory Record Form. Some forms may be developed as needed for specific types of data or classes of structure. NBI Sheet. A printed copy with abbreviated names of the numerical data in the electronic Bridge Inspection File. NBI stands for National Bridge Inventory, which must include all the information required by HIB. Permanent Structure Number (PSN). A unique three‐digit number assigned to any structure meeting the definition of a bridge. It is part of the 12‐digit Bridge Identification. PSNs are assigned by Control in ascending order as the bridges are built and are not necessarily in sequence along the Control or Section. An on‐system bridge replaced by a new bridge at the same location will have a new number assigned. A widened or reconstructed bridge will retain the same number. Shabiyas assign similar unique numbers to off‐system bridges. An off‐


system bridge replaced by a new bridge will retain the same PSN. A bridge with a longitudinal open joint in the middle will have two PSNs, even if the substructure is common. Route Over or Under. A bridge at intersecting highways is defined as an underpass or overpass based on the inventory hierarchy of the two routes. This description is used where required on all forms, plans, etc. The lower route takes precedence if the highways are of equal hierarchy. Signing and Sealing. The Engineer must sign and date many of the documents prepared for a bridge inspection. Work Authorization. Authorization issued by HIB to a Contractor (Engineer) to perform inspections of bridge structures. The Work Authorization is normally issued for a specific period of time with a commencement and ending date specified. To receive Work Authorizations, Contractors must pre‐qualify by demonstrating that they and their staffs are competent to inspect bridges.

13.7.3 Contractor Requirements General Requirements Contractor (Engineers) engaged by RBD to perform routine bridge inspections must adhere to the following general requirements in addition to those normally expected for Contractors. The Contractor (Engineer) must inspect each bridge in accordance with the information given in this Manual and must record the findings electronically and on the appropriate standard forms. The Engineer must uphold a reasonable standard of care for routine inspections, which is understood to imply an attentive visual and auditory inspection aided by routine inspection tools as afforded by customary means of access. The Engineer must inspect the bridges within the assigned inspection areas only and must verify the bridge locations. A qualified Inspection Team Leader must be present at each bridge site during the bridge inspection. When the inspections are completed, reports are to be returned to RBD within 30 days from the date of inspection. However, bridges needing special consideration (which includes all bridges that have any Condition Rating of 4 or lower) must be brought to the immediate attention of the RBD, both verbally and in writing. If the inspection indicates significant deterioration of any structural element, documentation such as notes, measurements, sketches, and photos must be included. Tools and Safety Equipment Routine inspection tools are listed in this Manual. The Engineer is required to use hard hats, safety vests, traffic cones, vehicle safety lights, and “Bridge Inspection Ahead” or “Survey Crew Ahead” signs for all bridges being inspected. The inspections must be conducted with minimal disruption to traffic.


Coordination with Housing and Infrastructure Board Roads and Bridge Department (HIBRBD) An 216 x 279 mm copy of the bridge location map, with the bridge location highlighted, must be included as part of each Bridge Record. New bridges located by the Engineer require approval from RBD before an identification number (Permanent Structure Number) is assigned and before authorization can be given for the Engineer to inspect the bridge and add the data to the Bridge Record. Bridge locations must be indicated on the map(s). The Engineer must create a new Bridge Folder, complete all forms, and input all data required for the electronic Bridge Inventory File to ensure a complete and accurate record. The Engineer must not inventory or inspect a bridge that is under construction. If the bridge opens to public traffic at a reasonable time within the work authorization period, RBD may direct the Engineer to inventory and inspect the bridge.

13.7.4 Coding Guidelines Summary of Instructions (for onand offsystem bridges) The Engineer must adhere to the step‐by‐step instructions for entering the data in the electronic Bridge Inventory File as presented in the detailed instructions for coding guide. The Coding Guide also includes interpretations, examples, and other data input guidance. The Coding Guide follows a “card” data input sequence summarized on a five‐page form not actually used for written entries but used as an input reference guide. A form could still be used, but data are usually directly input electronically using prompt screens on a computer, or screen images of the “card” data sequences. In any case, the resulting electronic Bridge Inventory File for each bridge is in a consistent format. The data entry procedures apply to both on‐ and off‐system bridges. The electronic Bridge Inventory Files contain a record for each Bridge Class Structure . The definition of a Bridge Class Structure is described in Item 112 in the “Instructions for Coding Guide.” MultiplePipe Culverts (for on and offsystem bridges) To achieve future consistency in recording information, the following clarifications are to be used for creating or maintaining Bridge Records for multiple‐pipe culverts:

• Do not remove any existing multiple‐pipe culverts from the Bridge Inventory File. The installation may already be in the prioritization process for repair or replacement, and the process should not be disrupted.

• Do not create Bridge Records for any new multiple‐pipe culverts that are individually less than

1500 mm in diameter even if the total installation, including fill between pipes, is more than 6.0 M along the roadway. Inspections of smaller diameters would be difficult to make and the results would probably be of dubious quality. It is also very inconsistent engineering logic to require inspection of, for instance, an installation of five 1200 mm pipe culverts and no


inspection of an installation of four or fewer pipes of the same diameter.

• Bridge Records must be made and maintained for multiple‐pipe culverts that are individually 1500 mm or greater in diameter, providing the total installation meets the 6.0 M length criterion.

Data Quality (for onandoff system bridges) Data quality for all information kept for each bridge, and in particular the electronic Bridge Inventory Files, cannot be overemphasized. The data in the files must be kept in as up‐to‐date condition as possible. Data updates reflecting changes to an existing on‐system structure must be made within 90 days of the evaluation or inspection that denotes the change in status. New, rebuilt, or rehabilitated structures also must be reported within 90 days of job completion. The data update time limit is 180 days for off‐system structures. Elements Data (only for onsystem bridges) Element‐specific data are to be recorded for each bridge. The step‐by‐step instructions for entering the electronic Elements Data are presented in the Elements: Field Inspection and Coding Manual. The instructions in the “Elements: Field Inspection and Coding Manual” also include interpretations, examples, and other data input guidance. The Engineer must determine the element‐specific data, quantities, and condition states for each on‐system bridge. HIB requires the Engineer to complete or demonstrate completion of special training for recording Elements Data. There are currently 6 “Element Matrix” forms presented in the “Elements: Field Inspection and Coding Manual.” These data supplement but do not replace those data normally recorded for the electronic Bridge Inventory File. The Elements Data are also recorded electronically. A copy on computer diskette in the required format is submitted to the RBD.

13.7.5 Forms General Forms Information Specific forms and other information used to record the necessary bridge data are briefly described below for both on‐ and off‐system bridges. The same data are kept for both on‐and off‐system bridges except as noted. The forms and necessary information are to be completed for each bridge and placed in each file of the Bridge Folder in the proper order. Subsection 13.55, Ratings and Load Posting, discusses Bridge Inspection Record Form and Bridge Appraisal Worksheet From and relates them directly to the Condition Ratings and Appraisal Ratings. Bridge Inspection Record, (for on and offsystem bridges) This three‐page form presents the inspection information for the basic components of the bridge. The Engineer enters a rating for each element of each component . For any element rating of 7 or below, written comments explaining the rating must be included on the form. The signature of the Inspection Team Leader must be on the form and it must be signed and dated by the Engineer.


Bridge Appraisal Worksheet, (for on and offsystem bridges) This two‐page form presents a one‐digit rating for each of the traffic safety features, the structural evaluation, the deck geometry, the under‐clearances, the load posting, the waterway adequacy, and the approach roadway alignment. It is also to be completed in accordance with the “Instructions for Coding Guide.” Unlike BIR Form , BAW Form requires written comments supporting all the appraisal ratings. These ratings and associated written comments must be verified by the Inspection Team Leader and reviewed by the responsible Engineer. A date and signature are required for this form Bridge Structural Condition History (for on and offsystem bridges) This form summarizes the current and previous inspection records. If the form exists in the current Bridge Folder, it should be updated. If no Structural Condition History form is in the Bridge Folder, create one based on all the previous and current inspections in the folder. The Engineer must enter the date(s) of inspection, the Engineer’s name, and the various component ratings in the proper columns of the form. This form does not require signing . However, the last entry date must reflect the latest inspection. Bridge Inspection FollowUp Action Worksheet (only for onsystem bridges) This form summarizes the areas of deterioration and makes recommendations for bridge repair. The number for the HIB R&B Department should be clearly shown on the form. An extra copy of this form is required for each on‐system bridge. These extra copies are grouped with copies for other bridges with the RBD. These extra copies must be submitted to the RBD at the end of each series of inspections or at the end of the inspection Work Authorization if done by a Contractor. Bridge Inventory Record, (for on and offsystem bridges) This two‐page form presents a detailed description of the structure along with a detailed elevation sketch on the reverse side. Sketches are not required for off‐system bridges if copies of the plans are in the Bridge Folder. Sketches are not required for on‐system bridges if plans are maintained in general files by HIB R&B Department. However, a notation to this effect should be shown on the reverse side of the form along with the Plan File reference number. If no changes have been made to the structure and the existing description and sketch properly represents the field conditions, a new form is not necessary. The existing form must remain in the Bridge Folder with no modification by the Engineer. If no Bridge Inventory Record is in the Bridge Folder, the responsible Engineer must complete a new form. The number for the Bridge Maintenance Section should be clearly shown on the form. The form must be signed and dated by the Engineer.


If significant structural modifications have been made to the bridge, a new Bridge Inventory Record, including a detailed sketch showing the changes from the plans on file, must be completed. The new form must be signed, sealed, and dated by the Engineer. The Bridge Inventory Record with sketch serves as the best available “as‐built plans” if copies of the original plans are not available. When plans are available and copies are included or the HIB file location referenced, a detailed sketch on the reverse side of the form is not required. Bridge Inventory Record Revision (for on and offsystem bridges) This form is to be used only for minor, non‐structural changes to the Bridge Inventory Record. This form does not require signing. However, a date is required. Channel CrossSection Measurements Record (for on and offsystem bridges) This two‐page form is completed or updated for each bridge over a waterway (wet or dry). There is space on the form for four chronological cross‐sections (covering approximately eight years). The fifth and following channel cross sections should be recorded on a new form and the original form retained in the Bridge Folder. This form is not required for bridge‐length culverts. The cross‐section measurements are recorded for the upstream side of the bridge starting at the first abutment. They must be from the top of the bridge railing or parapet down to the channel bed. These measurements are made at each bent, each significant change in the channel bed, and at the mid‐point of the channel. The horizontal distance is recorded between each vertical measurement as well as the cumulative horizontal distance from the beginning of the first abutment. Several additional reference dimensions are recorded, including top of water level as shown on the form. The responsible Engineer must add comments on the back of the form. This form require a date and signature. A sketch on this form is required only for span‐type bridges. Bridge‐length culverts do not require an upstream channel sketch or an update to any such sketch that may already be in the Bridge Folder. Calculations of sediment material quantities will not be required. If there is an existing channel cross‐section, plotted to scale, it should be brought forward into the current sketch and the new data plotted on it in different color ink and referenced with the Engineer’s initials and date. For all bridges that have plans available, the current channel section must be plotted on a copy of the bridge layout sheet(s) made from the plans. Two copies of the layout must be inserted in the Bridge Folder. One copy must be plotted with the current channel cross section and marked as a “work copy” and one copy must be identified as a “master copy” with no plot of the current channel cross section. If plans are not available, a sketch is to be drawn to scale. However, the horizontal and vertical scales may differ if convenient. This sketch does not require signing or sealing. However, a date is required for each plot or verification of the current channel cross section. Underclearance Sketch (for on and offsystem bridges) A sketch on this form is required for all grade separations, including pedestrian, utility, and railroad underpasses. All necessary dimensions and reference points must be shown. Item 54.2, described in the instructions for coding guide, must reference the minimum vertical clearance (to the nearest millimeters) under the structure. The vertical clearance sign must read 75 mm lower than the actual measured vertical clearance. Ultrasonic measurements cannot be used This sketch does not require


signing. However, a date is required. Bridge Summary Sheet (only for offsystem bridges) This one‐page form summarizes each component rating, provides recommendations for structure upgrades, indicates previous and observed and recommended load postings, records current status of all signs, and denotes materials needed to properly load post the bridge if necessary. The Engineer must, where appropriate, provide a recommendation for minimum or moderate upgrading for each bridge with an Inventory Rating of HS‐13 or less. The recommendation should consider the capabilities of the local jurisdiction. The Engineer must document the condition, location, and number of all signs in place on the date of inspection at all load‐posted bridges. The load limit shown on existing signs must also be recorded. These signs must appear and be legible in the bridge photographs. The form must be signed and dated by the Engineer. Recommended Change in Bridge Load Zoning, (only for onsystem bridges) This form presents a request for changed load restrictions for an on‐system bridge. It must be signed and dated by an Engineer. If it involves a new limit or a reduction of a current load limit, it must be accompanied by the most recent inspection report, plans (layouts and structural details), and any load ratings that support the recommended change.

13.7.6 Calculations

General Calculation Requirements Bridge load rating calculations must be provided in accordance with currently accepted HIB bridge inspection procedures as described in this Manual and in the HIB Bridge Manual. Note that the methods of calculation are different for on‐ and off‐system bridges. The dating and signing of documents must be in accordance with the requirements given in this chapter. OnSystem Bridge Calculations Typically, on‐system bridge plans are on file at the RBD office and the plans contain documentation of the original design load capacity. Load rating analyses (calculations) are usually not required for on‐system bridges. However, the Engineer is required to provide load rating analysis for all on‐system bridges that have any Condition Rating of 4 or less. All on‐system bridge files for all bridge types must contain documentation to support any recommended changes in load ratings. If the Engineer agrees with the previous calculations, a concurring signed and dated statement must be provided. All load rating calculations for on‐system bridges must be performed using the Load Factor (LF) method as presented in the AASHTO Manual for Condition Evaluation of Bridges

with no exceptions. Ratings must be calculated and presented to RBD with only an HS‐loading for all on‐system bridges for which calculations are required. Some additional analyses may involve bridges that have section loss or damage to structural members. In these cases, the responsible Engineer is required to verify and document the conditions of the deficient members and incorporate those findings in the analyses.


All calculations and documentation referring to load‐rating capacity are required to be signed and dated by a qualified, Professional Engineer. OffSystem Bridge Calculations The calculations for off‐system bridges may be performed using a Bridge Load Rating (BLR) computer program, which calculates load ratings using a working stress (WS) analysis method. However, either WS or LF analysis is acceptable. All steel, and truss bridges must have calculations for the load ratings of all applicable structural elements including the deck, stringer or beams, truss members, bent caps, and piling or columns. The BLR program will give Inventory and Operating Ratings for both H‐ and HS‐loadings. However, the recommended load‐posting sign must continue to be based upon Figure 8‐1, Simplified Load Posting Procedure, which relates calculated H‐load rating to an equivalent load posting, sign type, and weight limit. Load rating documentation, including assumptions, is required in the bridge files for all bridges, including bridge‐class culverts. Any assumed load ratings for concrete structures and recommended load postings must be in conformance with current HIB policies. These policies are described in Subsection 13.4 Customary Rating Procedures, Rating Concrete Bridges with no Plans, Recording Appraisal Ratings, Bridge Posting. All off‐system bridge files, for all bridge types, must contain documentation to support any recommended changes in load ratings. If the Engineer agrees with the previous calculations, a concurring signed and dated statement must be provided. All calculations and documentation referring to load‐rating capacity are required to be signed and dated by a qualified Professional Engineer. However, it is acceptable to only initial and date the calculations and sign, and date the Bridge Summary Sheet for off‐system bridges rather than each page of the calculations. Special attention is called to the coding of Items 41, 41.1, and 41.2 of the electronic Bridge Inventory Files (see coding guide) relating to operational status and load‐posting limits. These items must be verified and revised, if needed, for all bridges and bridge‐class culverts. The Engineer must immediately notify the RBD of any bridges recommended for closure and must include details and calculations. RBD will set a time to discuss the concerns with the Engineer to review the findings if bridge closure is necessary.

Simplified Load Posting Procedure

This procedure is appropriate for computing posting loads equivalent to the inventory rating. Approximations are involved which make this procedure unacceptable at load levels higher than the Inventory Ratings.

The posting load in pounds is the product of the RATING MULTIPKIER and the INVENTORY RATING in Tons for the standard “H” truck. In selecting the RATING MULTIPLIER from the table use the longest simple span length or 80% of the longest continuous span length, whichever gives the longest span length for the bridge. If the resulting span length is 48.0 M or greater, then the bridge should receive an analysis more exact than this procedure.


The recommended posting increments are listed below. Round off to the nearest increment listed.

Post axle and gross load for span lengths 12.0 M and greater. Post axle load only for span lengths 12.0 M and less. Weight limit signs should conform to the Traffic Management Section of HIB Design Criteria. The recommended signs are R12‐2Tb or R12‐4Tb except if the axle load is noted “ use signs R12‐2Tc or R12 ‐4Tc.

EXAMPLE 1: 10.0M Simple Span Slab & Girder Bridge, H14 Rating Axle = 14 x 660 Kgs = 9240 Kgs Post 21,000 tandem axle (Signs R12‐2Tc) EXAMPLE 2: 36.0M Pony Truss. H7 Rating Axle =7 x 660 = 4,620 Kgs Gross = 7 x 1045 Kgs = 7315 Kgs Post 4545 Kgs axle or tandem and 7273 Kgs Gross (sign R 12 ‐4Tb) EXAMPLE 3: 9.0 M – 12.0 M – 9.0 M Continuous Slab Bridge with 7.6 M slab approach spans, H10 Rating 0.8 x 12.0 M = 9.0 M > 7.6 M = Use 7.6 M span Axle = 10 x 673 Kgs = 6730 Kgs Post 673 Kgs Axle or tandem (Sign R 12 ‐2Tb)


SPAN

AXLE

OR GROSS

TANDEM

METER Kgs ./H‐TON Kgs/H‐TON

‹6 727

7.6 704

9.1 682

10.7 659

12.2 659 1410

13.7 659 1340

15.2 659 1270

18.3 659 1180

21.3 659 1140

24.4 659 1110

27.4 659 1090

30.5 659 1070

36.6 659 1040

42.7 659 1020

48.8 659 1000

RATING MULTIPLIER

LOAD INCREMENTS LOAD INCEMENTS

FOR AXLE OR FOR GROSS LBS

TANDEM Kgs

2270 3640

3410 4540

4540 5450

5680 6360

6820 7270

7940 9090

9540 10910

10910* 12730

12730* 14540

14540* 16360

18180

20000

21820

23640

27270

30910

34540

* Axle load exceeds 9090 Kgs . Single axle

l imit, therefore post for tandem axle

(Signs R 12 ‐2Tc or R 12‐ 4Tc)


R12 – 2Tb R12 – 2Tc R12 – 4Tb R12 – 4Tc 60mm x 90 mm 60 mm x 105 mm

13.7.7 Data Submittal General Data Submittal Requirements (for on and offsystem bridges) When HIB contracts for bridge inspections by Contractors, the Contractors must provide monthly submissions of prepared Bridge Folders unless otherwise directed by the RBD. Folders can be submitted to the RBD by mail or in person. Bridge Folders prepared by RBD personnel must be documented, signed and dated in the same format as herein described. All data included in the Bridge Folder are prepared to meet the requirements given in this Manual. Updates to the electronic Bridge Inventory File must be made within 90 days for on‐system bridges and 180 days for off‐system bridges.


Photographs (for on and offsystem bridges) The Engineer must provide 100 mm x 150 mm color photographs of each bridge for the bridge inspection files. The photos must be suitably mounted, two on a page, with compatible adhesive on 216 mm x 280 mm paper. Spray‐on adhesive is not acceptable. Each photo must have a descriptive caption and must note the approximate compass direction the photographer was facing. Each photo will have a date taken as part of the caption unless the date is automatically printed on the photo. Digital photographs will be accepted at a minimum resolution of 1024 x 768. They are to be presented in the same format and dimension as described above. The following photos must be present in each Bridge Folder as a minimum: Roadway View. Photos must be taken along the centerline of the roadway looking “down the bridge” showing views of the bridge as seen from the roadway. The direction should normally be in the increasing station direction, if known, or in the increasing direction of the field reference markers. Long or curved bridges may require multiple photos at different bridge locations. Elevation View. Photos must be taken of the bridge showing the complete length. For some bridges it may be impossible to show the entire structure due to length, curvature, or vegetation. In these cases, oblique angles at greater distances are acceptable. However, multiple photos attempting to show every part of the bridge should not be submitted. Underside View. Photos must be taken of the underside of the bridge showing the typical type of superstructure. Bridges with several types of superstructure will require additional photos. Stream or Roadway below Bridge. Photos should be taken from below the bridge showing the stream or roadway as it passes under the bridge. Any scour or significant erosion that is present should be photographed. Weight Limit Signs. Photos must be taken on both approaches to document the actual signs in place, missing, or damaged. The photos must show the position of the signs with respect to the bridge. The weight limit on the signs should be legible in the photos. Upstream and Downstream Channel Views. Photos must be taken to document the condition of the channel upstream and downstream of the bridge. These photos should be taken from the bridge. Photos of Components with Poor Condition. Photos must be taken of all elements that result in Component Ratings of 4 or less on the Bridge Inspection Record. Details of the Condition Rating for the deficient elements must be noted in the photo captions. However, multiple photos are not needed within a deficient element. For instance, a poor superstructure component rating due to a deficient floor beam does not mean that detailed photos must also be taken of all the elements making up the superstructure component. Photos of Unusual Features. Photos should be taken of features which, in the opinion of the inspector, are unusual, non‐standard, or poorly repaired. For instance, a bridge railing field fabricated from non‐standard parts which may not be equivalent to an acceptable bridge railing should be documented by


close‐up photos. The Engineer must determine if it is appropriate to submit these photos as part of the Bridge Record. Photos of utility attachments should also be made with enough detail to show the type, condition, and attachment hardware used. Electronic Media (for on and off system bridges) The Engineer must provide all applicable electronic data for the Bridge Records on a CD/DVD or Flash Memory stick. Multiple bridges may be submitted on the same diskette; however, they should be grouped by local jurisdiction, maintenance section, etc. Presentation of Documents (for on and offsystem bridges) The Engineer must ensure that all inspection results submitted to the Bridge Inspection Division are typed, using the current versions of the electronic forms where applicable, and are of such quality that legible reproductions can be made on a typical office copy machine. All copies and records submitted to be placed in the Bridge Folder should be 216 mm x 280 mm unless another size is allowed by HIB for the specific application. However, copies of bridge plans may be A3 size paper. The Contractor Engineer must provide the RBD with the following information in list format at the end of the Work Authorization. These lists are not placed in the individual Bridge Folders. The lists should be grouped by jurisdiction such as shabiya,, municipality, city, maintenance section, etc.

List of bridges recommended for special inspections. This list must include only bridges to be added to the current list of bridges with fracture‐critical details or bridges with the need for underwater (scuba diver) inspection. Bridges currently on the fracture‐critical and underwater lists need not be placed on this new recommended list.

List of bridges with poor condition rating. This list must include all bridges that have an individual element or component with a Condition Rating of 4 or less.

List of bridges with over‐height load damage. This list must include all bridges which have damage from over height loads or which have had repairs made after such damage. The extent of the damage must be documented on the Bridge Inspection Record, and Item 128 of the electronic Bridge Inventory File must be coded.

List of bridges with cracked pre‐stressed beam ends. This list must include all bridges that have pre‐stressed box beams or pre‐stressed concrete beams with cracks at or near the beam ends. Photos of these cracks must be taken. If common to several beams in the bridge, only representative photos are needed. The severity, number of cracks, and specific location of each cracked beam must be indicated.

List of bridges requiring changes in Operational Status. This list must include all bridges that do not meet current HIB load posting policy requirements for posting load restrictions. This policy is described in Chapter 5 in the subsection titled Load Posting. The bridges on this list should be grouped by local jurisdiction. Bridges are not to be placed on this list which currently have a load posting and for which no change is required.


List of bridges requiring vertical clearance changes. This list must include all bridges requiring changes in the vertical clearance data as indicated by Item 54.2 of the electronic Bridge Inventory File (see the coding guide). Even though only minor changes in the actual vertical clearance may have occurred due to a pavement overlay, the updated data are necessary so RBD can maintain the information needed for over‐height load permits.

List of bridges with suggested changes to “blocked” data fields. This list must be submitted for changes to the blocked data recommended by the Engineer. These data will be reviewed and updated only by the HIB R&B Department.

Original and Duplicate Files (for onsystem bridges) For each on‐system bridge, the Engineer is required to submit to the RBD one original and one duplicate Bridge Record. One additional copy of the Bridge Inspection Follow‐Up Action Worksheet (only used for on‐system bridges) will also be required. This worksheet is described in the Forms section of this chapter.

• Original Bridge Record. The original bridge record must be submitted clipped into the six‐sided Bridge Folder discussed in the following Bridge Folder section of this chapter. The order of the various forms, sketches, photos, etc in the Bridge Folder must be made uniform with no exceptions. This original Bridge Record will contain the originals of all documents created or updated by the Engineer, including photos.

• Duplicate Bridge Record. A duplicate file must be submitted and clipped into a manila folder

that must contain copies of all the documents prepared by the Engineer, including color copies of all the mounted photograph sheets with captions.

Additional Files (for offsystem bridges) For each off‐system bridge, the Engineer must submit one Original Bridge Record as described above, and one set of Summary Reports which are described below. A Duplicate Bridge Record is not required for off‐system bridges. Summary Reports (for offsystem bridges) The items to be included in the Summary Reports must be grouped for all the bridges within each local jurisdiction. The bridges included in each local jurisdiction (regions, municipalities, cities etc.) must be as agreed upon with the RBD. The arrangement and content of the Summary Reports will be maintained. The Summary Reports are intended to summarize the bridge inspection findings, maintenance or repairs needed, and load‐posting requirements. The Summary Reports, whether prepared by the Contractor or by RBD personnel, must be assembled as shown in a typical example which can be obtained from the RBD. The Summary Report must be delivered to the RBD. The RBD will forward the Summary Report to the local jurisdiction. Each Summary Report must include the following information for each bridge:

• Color copies of the mounted photograph sheets including captions


• A copy of the Bridge Inspection Record

• A copy of the Bridge Summary Sheet. Summary of New LoadPosting Materials (for offsystem bridges) This form is used to order the signs and hardware needed for each off‐system bridge which requires a change in the load posting. The Engineer must complete this form for each group of bridges within each local jurisdiction. The bridges included in each local jurisdiction (shabiyas, municipalities ,cities) must be as agreed upon with the RBD. This completed form will be used to ensure that the necessary materials are available to load post the bridges in each local jurisdiction. The Engineer will submit this form to the RBD. It must never be submitted in any form to any local jurisdiction. This form does not require signing. However, a date is required. Scour Records and Reports (for on and offsystem bridges) Many bridges are susceptible to scour of the foundations and abutments from flowing water. These bridges are screened and classified for their potential for scour. Various scour reports, calculations, and photos are necessary to document the scour potential. The scour information for most bridges can usually be directly included in the Bridge Folder. However, some bridges have extensive scour data, and the location of external scour files must be cross‐referenced in the Bridge Folder. The RBD must determine the amount of scour documents to be included with each Bridge Folder.

13.7.8 The Bridge Folder Folder Information (for on and offsystem bridges) The original records, sketches, plans if available, and latest information on each bridge on Libya highway system are kept in a consistent and regular manner by RBD. Folder Assembly (for on and offsystem bridges) Each Bridge Folder must have an encompassing folder containing two dividers to which documents can be fastened. Beginning with the inside surface of the front cover (hereafter called Side 1) and ending with the inside surface of the back cover (Side 6), the information consists of and is assembled in the following order in the Bridge Folder. For the Duplicate File required for on‐system bridges, which is placed in a manila folder without dividers, the information should be assembled in the same order from top to bottom, ignoring the “Side” number. Side 1 Top 1. Location Map with bridge highlighted

2. All current inspection photos (including those with low condition ratings) 3. All other photos from previous inspections in chronological order (negatives may be

removed at the discretion of the HIB R&B Department.


Side 2 Top 1. Bridge Summary Sheet (off‐system)

2. Bridge Inspection Follow‐Up Action Worksheet (on‐system) 3. Bridge Inspection Record 4. Bridge Appraisal Worksheet 5. Current Load Rating Calculations or copies of bridge plans; a reference to the HIB R&B

Department Plan File Designator or “Tab Number” for the plans is also acceptable 6. Bridge Inventory Record (must include proper sketch(s) if bridge plans are not on file) 7. Bridge Inventory Record Revisions (if applicable)

Side 3 Top 1. Under‐clearance Sketch (if applicable)

2. Upstream Channel Cross‐Section Measurements (if applicable) 3. Upstream Channel Cross‐Section Sketch (if applicable)

Side 4 Top 1. NBI Sheet (printout of the electronic Bridge Inventory File)

2. Secondary Scour Screening Form (if applicable) 3. The list of scour susceptible bridges with their scour classification 4. Any scour‐related reports or documents (if applicable); reference to the HIB file location is

also acceptable 5. All scour photos

Side 5 Top 1. Elemental Data Inspection Records

2. Special Inspection Records and Reports (Underwater Inspection, Fracture Critical Inspection, etc)

Side 6 Top 1. Bridge Structural Condition History

2. Previous inspections and all attachments in reverse chronological order (the most recent information is attached on top)

3. Bridge plans if available


13.8 Appendix

Bridge Inspection Forms

1. Bridge Inspection Record

2. Bridge Appraisal Worksheet

3. Bridge Structural Condition History

4. Bridge Inspection Follow‐up Action Worksheet

5. Bridge Inspection Follow‐up Action Worksheet

6. Bridge Inventory Record

7. Bridge Inventory Record Sketch

8. Revision to Bridge Inventory Record

9. Channel Cross‐Section Measurements Record

10. Channel Cross‐Section Measurements Record

11. Under‐clearance Record

12. Bridge Summary Sheet

13. Recommended Change in Bridge Load Posting


BRIDGE INSPECTION REPORT

Page 3 of 3

Comment Sheets: (Per Item, if any)

JUNE 2009 REVISION NO. 02 ELECTRICAL 14‐1

14 Electrical

All electrical work shall be coordinated with General Electric Company of Libya (GECOL) and other utility service providers. The design shall be in compliance with GECOL Documents and HIB Master Specifications and Standard Details. The GECOL Specifications and design criteria should be issued to the contractors by HIB.

JUNE 2009 REVISION NO. 02 TELECOMMUNICATION 15‐1

15 Telecommunication

All telecommunication work shall be coordinated with Libyan Post, Telecommunication and IT Company (LPTIC) other utility service providers. The design shall be in compliance with LPTIC Documents and HIB Master Specifications and Standard Details. The LPTIC Specifications and design criteria should be issued to the contractors by HIB.

JUNE 2009 REVISION NO. 02 GAS Distribution 16‐1

16 Gas Distribution

All gas distribution work shall be coordinated with General Gas Company (GGC) of Libya and other utility service providers. The design shall be in compliance with GGC Documents and HIB Master Specifications and Standard Details. The GGC Specifications and design criteria should be issued to the contractors by HIB.

2009.06Design Criteria for Infrastrcture Projects-Rev 02 Final June

Documents

Transcript of 2009.06Design Criteria for Infrastrcture Projects-Rev 02 Final June