Capacity Level of Service-transport
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Transcript of Capacity Level of Service-transport
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Freeway & Highway Level of Service
CETB 414NI-UNITEN
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Chapter
Capacity And Levelof Service
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Outline
1. Definitions2. Level of Service (LOS)3. Freeway Segment LOS Determination
a. Free-flow speedb. Flow Rate
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Freeway Definition
A divided highway with full control ofaccess and two or more lanes for the
exclusive use of traffic in each direction. Assumptions
No interaction with adjacent facilities (streets,other freeways)
Free-flow conditions exist on either side of thefacility being analyzed
Outside the influence or ramps and weaving areas
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Basic Freeway Segment
From Highway Capacity Manual , 2000
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Base / Ideal Condition for Freeway 3.6 m (12 ft) minimum lane widths. 1.8 m (6 ft) minimum clearance between the
edge of travel lanes and the nearest roadsideobstructions.
0.6 m (2 ft) minimum median lateral clearance Traffic stream consists of passenger cars only 10 or more lanes (both direction -in urban area
only)
Interchanges spaced every 3.3 km Level terrain with grades no greater than 2
percent Driver population dominated by regular and
familiar users of the facility (commuter) C E T B
4 2 3
H i g h w a y
D e s
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& T r a
f f i c E n g
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Free-Flow Speed
Free-Flow Speed (FFS) The mean speed of passenger cars that can be
accommodated under low to moderate flow rateson a uniform freeway segment under prevailingroadway and traffic conditions.
Factors affecting free-flow speed Lane width - Driver population Lateral clearance - Geometric design Number of lanes - Interchange density Vehicle equivalents
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Freeway capacity
The maximum sustained 15-min flow rate,expressed in passenger cars per hour per lane(pc/hr/ln), that can be accommodated by a uniform
freeway segment under prevailing traffic androadway conditions in one direction of flow.
Number of lanesLanes width
Lateral obstructionInterchange spacing
Grade
Traffic compositionDriver population
speed
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Free-Flow Speed
Free-Flow Speed (FFS) The mean speed of passenger cars that can be
accommodated under low to moderate flow rateson a uniform freeway segment under prevailingroadway and traffic conditions.
Factors affecting free-flow speed Lane width - Driver population Lateral clearance - Geometric design Number of lanes - Interchange density Vehicle equivalents ( Trucks and RVs behave differently)
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Definitions Level of Service (LOS) Qualitatively measures both the operating
conditions within a traffic system and howthese conditions are perceived by drivers
and passengers Related to the physical characteristics of the highway
and the different operating characteristic that canoccur when the highway carries different traffic
volumes (Different measures for different facilities)Lane width , lateral obstruction , grade, traffic composition , speed, driverpopulation
Six measures (A through F )
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Levels of Service
F r o m
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LOS A Free-flow operation with
low volume Density not greater than 7
pc/km/ln High speed
LOS B Reasonably free flow Ability to maneuver is only
slightly restricted Effects of minor incidents
still easily absorbed
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Levels of Service
LOS C Speeds at or near FFS Freedom to maneuver is
noticeably restricted Queues may form behind any
significant blockage.
LOS D
Speeds decline slightly withincreasing flows Density increases more quickly Freedom to maneuver is more
noticeably limited Minor incidents create queuing
F r o m
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Levels of Service
LOS E Operation near or at capacity No usable gaps in the traffic
stream Operations extremely volatile Any disruption causes queuing
LOS F
Breakdown in flow Queues form behind
breakdown points Demand > capacity
F r o m
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F r o m
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Freeway LOS
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From Highway Capacity Manual , 2000
Freeway LOS
Level of Service
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Freeway LOS
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LOS Calculation
Does not consider Special lanes reserved for a particular type of vehicle
(HOV, truck, climbing, etc.)
Extended bridge and tunnel segments Segments near a toll plaza Facilities with FFS < 90 km/h or > 120 km/h Demand conditions in excess of capacity Influence of downstream blockages or queuing Posted speed limit Extent of police enforcement Intelligent transportation system features Capacity-enhancing effects of ramp metering
Freeway LOS
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InputGeometric Data
Measured FFS or BFFSVolume
BFFS AdjustmentLane width
Number of lanesInterchange density
Lateral clearance
Volume AdjustmentPHF
Number of lanesDriver populationHeavy vehicles
Compute FFS Compute flow rate
Define speed-flow curve
Determine speed using speed-flow curve
Compute density using flow rate and speed
Determine LOS
BFFS Input
MeasuredFFS Input
Freeway LOS
F LOS
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Determining FFS
Measure FFS in the field Low to moderate traffic conditions
Use a baseline and adjust it (BFFS)
ID N LC LW f f f f BFFS FFS FFS = free-flow speed (km/h)
BFFS = base free-flow speed, 110 km/h (urban), 120 km/h (rural)
f LW = adjustment for lane width (km/h)
f LC = adjustment for right-shoulder lateral clearance (km/h)
f N = adjustment for number of lanes (km/h)
f ID = adjustment for interchange density (km/h)
Freeway LOS
F LOS
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Lane Width Adjustment (f LW )
Base condition (f LW = 0) Average width of 3.6 m or wider across all lanes
From Highway Capacity Manual , 2000
Freeway LOS
F LOS
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Lateral Clearance Adjustment (f LC )
Base condition (f LC = 0) 1.8 m or greater on left side
0.6 m or greater on the median or right side
From Highway Capacity Manual , 2000
Freeway LOS
USA
F LOS
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Number of Lanes Adjustment (f N) Base condition (f N = 0)
5 or more lanes in one direction Do not include HOV lanes
f N = 0 for all rural freeway segments
From Highway Capacity Manual , 2000
Freeway LOS
F LOS
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Interchange Density Adjustment (f IC)
Base condition (f IC = 0) 0.3 interchanges per km (3.3 km spacing) Interchange defined as having at least one on-ramp Determined over 10 km segment
From Highway Capacity Manual , 2000
Freeway LOS
F LOS
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Determining Flow Rate
Adjust hourly volumes to get pc/ln/hr
p HV p f f N PHF
V v
vp = 15-minute passenger-car equivalent flow rate (pcphpl)
V = hourly volume (veh/hr)PHF = peak hour factor
N = number of lanes in one direction
f HV = heavy-vehicle adjustment factor
f P = driver population adjustment factor
Freeway LOS
Freeway LOS
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Peak Hour Factor (PHF)
Typical values 0.80 to 0.95
Lower PHF characteristic or rural or off-peak Higher PHF typical of urban peak-hour
415V
V PHF
V = hourly volume (veh/hr) for hour of analysis
V15 = maxiumum 15-min. flow rate within hour of analysis
4 = Number of 15-min. periods per hour
Freeway LOS
Freeway LOS
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Heavy Vehicle Adjustment (f HV)
Base condition (f HV = 1.0) No heavy vehicles
Heavy vehicle = trucks, buses, RVs
Two-step process Determine passenger-car equivalents (E T) Determine f HV
Freeway LOS
Freeway LOS
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Determine f HV
111
1
R RT T HV E P E P
f
f HV = Heavy vehicle adjustment factor
ET, E R = Passenger-car equivalents for trucks/buses and RVs
P T, P R = Proportion of trucks/buses and RVs in traffic stream
Freeway LOS
Freeway LOS
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Passenger-Car Equivalents (E T)
Extended segments method Determine the type of terrain and select E T No one grade of 3% or more is longer than 0.4 km
OR No one grade of less than 3% is longer than 0.8 km
From Highway Capacity Manual , 2000
Freeway LOS
Freeway LOS
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Passenger-Car Equivalents (E T) Specific grades method
Any grade of 3% or more that is longer than 0.4 kmOR
Any grade of less than 3% that is longer than 0.8 km
From Highway Capacity Manual , 2000
Freeway LOS
Freeway LOS
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F r o m
H i g h w a y
C a p a c
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l , 2 0 0 0
Freeway LOS
Freeway LOS
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Passenger-Car Equivalents (E T)
Freeway LOS
F r o m
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l , 2 0 0 0
Freeway LOS
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Passenger-Car Equivalents (E T)
Composite grades method Determines the effect of a series of steep
grades in succession
Method OK if All subsection grades are less than 4%
OR Total length of composite grade is less than 1200 m
Otherwise, use a detailed technique in theHighw ay Capaci ty Manual (HCM)
From Highway Capacity Manual , 2000
Freeway LOS
Freeway LOS
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Driver Population Adjustment (f P)
Base condition (f P = 1.0) Most drivers are familiar with the route
Commuter drivers Typical values between 0.85 and 1.00
Freeway LOS
Freeway LOS
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Determining level of Service(LOS)
Directly determine from Speed-Flow curve
Determine the density of flow
Freeway LOS
Freeway LOS
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Define Speed-Flow Curve
Select a Speed-Flow curve based on FFS
From Highway Capacity Manual , 2000
Freeway LOS
Freeway LOS
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Determine Average PC Speed (S)
For 90 FFS 120 km/h AND (3100 15FFS) < vp (1800 + 5FFS)
For 90 FFS 120 km/h AND vp < (3100 15FFS)
6.2
130020
310015180023
28
1
FFS
FFS v FFS FFS S p
FFS S
Freeway LOS
Use v p and FFS curve to find average passenger car speed (S)
Freeway LOS
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Determine Density
Calculate density using:
S
v D
p
D = density (pc/km/ln)
vp = flow rate (pc/km/ln)
S = average passenger-car speed (km/h)
Freeway LOS
Freeway LOS
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From Highway Capacity Manual , 2000
y
Determine LOS
Freeway LOS
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From Highway Capacity Manual , 2000
y
Determine LOS
F r o m
H i g h w a y
C a p a c
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Freeway LOS
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Example 1
y
Existing 4-lane freeway, urban area with very restricted geometry.
3.3 m lane width 0.6 m lateral clearance on left and right sides rolling terrain interchange spaced 2 km apart 2000 vph peak hour volume (one direction) PHF = 0.92 Traffic consists of 5% truck Mostly commuter traffic.
Determine the LOS during peak hour.
Freeway LOS
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Example 2
y
Existing rural freeway
v ideal free flow speed of 120 km/hrv has two 3.6m lanes in each directionv 1.2m shoulder lateral clearance v Interchanges spaced approximately 5 km apart.v Traffic consists of 10% trucks and buses and 8%
recreational vehicles.v The adjustment for driver population factor is estimated to
be 0.80.v Peak 15 min flow rate is 1760 vph
Determine the LOS on a 1.7 km long 3.1% upgrade?
Freeway LOS
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Example 3
y
Existing rural freeway
v Ideal free flow speed of 120 km/hrv Rolling terrainv 1.2m shoulder lateral clearance v Interchanges spaced approximately 5 km apart.v Traffic consists of 10% trucks and buses and 8%
recreational vehicles.v The adjustment for driver population factor is
estimated to be 0.80.v Peak 15 min flow rate is 1760 vph
How many lanes to provide LOS B?How many vehicles can be added before the roadwayreaches capacity?
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Primary References
Nicholas J. Garber, Lester A. Hoel (2005). Traffic & HighwayEngineering , Third Edition. Chapter 9
Transportation Research Board. (2000). Highway Capacity Manual2000 . National Research Council, Washington, D.C.