Design Manual 1

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REPUBLICOFYEMEN

MINISTRYOF PUBLICWORKSANDHIGHWAYS

RURALACCESSPROJECT

CENTRALMANAGEMENTOFFICE(RAPCMO)

RURALROADS

DESIGNMANUAL

ISSUED:OCTOBER 2004

REVISED FEBRUARY 2005


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REVISED: FEBRUARY 2005


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SECTION 1

INTRODUCTION

Section

1


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Rural Roads Design Manual

Section 1 - Introduction

Republic of Yemen

Ministry of Public Works and Highways

SECTION 1INTRODUCTION

TABLE OF CONTENTS

Page

1.1 Background 11.2 Objectives 21.3 Scope 21.4 Design Process 31.5 RAP Roads Design Philosophy 6


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SECTION 1

INTRODUCTION

1.1 BACKGROUND

Insufficient infrastructure and inadequate access to social services have

been a major deterrent to rural development in Yemen. In 1995 there was

about 64,500 km of roads, 4,800 km of them paved (about 7.5%). Many

areas are inaccessible to vehicles leaving a large sector of the populationsuffering from accessibility problems to the basic services they need. In

1996 there were 229,000 passenger cars, a ratio of 31 people per car. In

remote areas people rely principally on non-motorized transport.

The Rural Access Program initiated by the Government of Yemen with

support from the World Bank aims at improving the livelihood and

reducing the isolation of the rural population in Yemen.

To achieve this objective, the Program will improve planning and

implementation of rural roads, thereby reducing a major obstacle to rural

economic growth caused by poor access. The Program will be implemented

in three phases:

Phase I : (2001 to 2005) is setting up the institutional and technicalf d ti f l d j t Th h h b


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1.2 OBJECTIVES

The Ministry of Public Works and Highways Rural Access ProjectCentral Management Office (RAP-CMO) is in the process of contracting

local consultants who will be responsible for the preparation of detailed

design and supervision of construction for a number of Rural Intermediate

Roads and Village Access Roads.

As a part of the capacity building process adopted by RAP for local

consultants, RAP has undertaken to develop comprehensive standards forrural roads to serve the country in effectively developing this sector.

This Design Manual addresses the needs of road engineers and designers

for safe, economical and environmentally sound designs of rural roads and

rural intermediate roads in Yemen at the levels of the Governorate, District

as well as Village Access. These roads are typically low volume roads with

average daily traffic in the range of 100-1000 vehicles per day, located in

various types of terrain and climatic conditions prevailing in Yemen.

1.3 SCOPE

The scope of work for developing this manual included review of existing

design guidelines and standards developed previously, comments from

MPWH and RAP, field visits undertaken to various projects sites,

di i ith lt t d t t ll th k h


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- AASHTOGuidelines for Geometric Design of Very Low-Volume

Local Roads (ADT 400).

- National Highway and Rural Access Master Plan Study Road

Classification System, Ministry of Public Works and Highways

Yemen.

- TRL Road Note 6A Guide to Geometric Design, 1988.

- TRL Road Note 31A Guide to the Structural Design of BitumenSurfaced Roads, 1993.

- TRL Road Note 19 A guide to the design of hot mix asphalt in

tropical and sub-tropical countries, 2002.

- TRL Road Note 40A guide to axle load surveys and traffic counts

for determining traffic loading on pavements, 2004.

- World Bank The Roads Economic Decision Model (RED),

SSATP working paper No. 78, July 2004.

- World BankRoads and the Environment Handbook.

- RAPCMOSectoral Environmental Assessment, Vol. 1, 2004.

RAPCMO S l E i l A V l 2 S f d


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Traffic analysis ofalternative routes

Economic analysis

Environmental Screeningand Categorization

2

9

10

Project, Planning,

Prefeasibility and

Feasibility Studies

Preliminary GeometricDesign

Geotechnical Studies

EA Consultations

and Impact Analysis

3

4

10

PreliminaryDesign

Geometric Design3

Project Process ActivitiesSection of this

Manual


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Republic of YemenMinistry of Public Works and Highways

DOCS-0974-04 1-5

EA

Phases EA Planning:

Project

Identification and

Project Concept

Preliminary and

Final DesignProject Tendering

Execution

Project Managementand Supervision

Project Completion

and Post Evaluation

Operation and

Maintenance

Project Cycle

Processes

Project Phases Operation &

MaintenanceConstructionProject Preparation and Design

Planning,Pre-feasibility and

Feasibility Studies

- Scoping and

Screening

- Identification of

issues and

applicable

safeguards policies.

- Categorization

- Action plan

CMO - E&S UnitResponsibilities

EA, SFA &

Consultations

- Draft EA

- Draft SFA

- Womenconsultations

- Disclosure of draft

EA and SFA to

communities

- Signing of Final

SFA

- Final version of EA

Consultant /

CMO - E&S Unit

Environmental

ContractSpecification

- Incorporation of

EMP into contract

documents

- Pre-tender briefing

CMO - E&S unit /Consultant, Districts

& Communities

Implementation and

Monitoring

- EMP

implementation

- Compliance

monitoring and

reporting on

environmental and

social mitigation

measures

Consultant /

CMO - E&S Unit

Post Evaluation

- Compliance

summary

- Unanticipated

impacts

- Lessons learned

ContractorsCMO - E&S Unit, RE

& Local Community

O & M Monitoring

- Compliance

monitoring and

reporting onenvironmental and

social mitigation

measures

ContractorsCMO - E&S Unit RE

& Local Community

EA

Activities

Figure 1.2- Integration of Environmental and Social Management Process in the Project Cycle


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1.5 RAP ROADS DESIGN PHILOSOPHY

The fundamental characteristics of rural roads that distinguish them fromother roads in the national network include:

- Low traffic volumes with ADT generally < 1000 vehicles per day,

with many roads having ADT 400 vpd. Such volumes of traffic

indicate that accident-prone encounters between vehicles are rare

events and the probability of collision is small.

- The rural and local access natures of these roads indicate that most

drivers using them are familiar with their nature as well as the

nature of the terrain traveled. This familiarity reduces the elements

of risk resulting from design features that may surprise unfamiliar

drivers, but are anticipated by familiar drivers.

- The nature of the mountainous terrain in Yemen makes it

economically prohibitive, or physically impossible to constructroads at the normal standards. Thus, relaxed standards are

necessary in order to ensure a cost-effective approach to the road

system. Relaxation of standards apply especially for roads in

difficult mountainous terrain and for road projects involving

existing tracks or existing alignments where full reconstruction is

economically unjustified. Thus the designer is encouraged to relax

the standards to avoid unnecessary improvement on existing

li b l l k f id f i ifi f


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safety conservative and risk-averse, providing a margin of safety that takes

into consideration a wide range of conditions that might occur on the road

system. They are not based on rigorous cost-effectiveness approach, buthave established values that are judged to be reasonable and prudent, given

overall costs, impacts, and benefits.

The design guidelines for very low-volume roads developed by AASHTO

are based on safety risk assessment which results in comparable margins of

safety presented in the AASHTO Policy on Geometric Design of

Highways and Streets for higher volume roads.

For rural low volume roads the design criteria should be based on tradeoffs

between, on one hand, differences in construction and maintenance costs,

and estimated impacts on safety. This makes cost-effectiveness as the

appropriate basis for defining minimum design criteria or values for low

volume rural roads.

This Manual is prepared to be a fairly comprehensive document and tocover all the important elements of rural road designs encountered by

RAP. Yet, no manual can supersede good engineering judgment and

the application of sound principles by knowledgeable designers who

can tackle unique and often conflicting design requirements and

develop tailored solutions to specific design problems.


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SECTION 2

ROAD CLASSES, DESIGN SPEED

AND TRAFFIC

Section

2


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Section 2 - Road Classes, Design Speed and Traffic

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SECTION 2ROAD CLASSES,DESIGN SPEED AND TRAFFIC

TABLE OF CONTENTS

Page

2.1 Introduction 12.2 Road Classes 12.2.1 Roads Functional Classification 12.2.2 RAP Roads Design Classes 42.3 Design Speed 62.3.1 Design Speed Criteria 62.3.2 Design Speed Standards 72.3.3 Relaxation of Standards 72.4 Traffic 102.4.1 Design Life 102 4 2

B li T ffi Fl E ti ti 11


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SECTION 2

ROAD CLASSES,DESIGN SPEED AND TRAFFIC

2.1 INTRODUCTION

The criteria used in the geometric design shall be pertinent to the local

conditions with respect to technical application and development trends.

They shall further be economically feasible, taking into consideration all

the relevant conditions and circumstances such as climate, topography andgeotechnical conditions encountered in the different regions of the country.

The design standards shall not impose any limits on the needs of society for

the development of transportation and the implementation shall be

undertaken with due regard to all relevant data and conditions, both

existing and forecast. In this Section of the Manual, special emphasis has

been placed on the functional classification of roads and as these are

considered the most important parameters for harmonization of RAP road

projects within the national road network.

Economic constraints may justify adoption of lower geometric standards

than are desirable, but economic restrictions will not justify abandoning a

balanced geometric design by downgrading only some of the design

elements, as for example, reducing the formation width without adjusting

th d i d di l H th t i d i ill


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This functional concept is important to the design of new roads, and is

consistent with a systematic approach to design and transportation

planning.

In general, the system consists of primary, secondary and tertiary networks

according to mobility and function, importance at the national level, and

administrative jurisdiction.

The Road Classification System recommended by the National Highway

and Rural Access Master Plan Study (NHRAMP) emphasizes the attribute

of administrative responsibility. The rationale is to enable the enactment of

Law No. 4 of 2000 on Local Authority, whereby Mohafazas and Mudiriyas

will in the future assume the responsibility for Secondary and Tertiary

Road Networks in their respective areas. The following classification has

been recommended:

i. National (Primary) Road Network

Jurisdiction: Ministry of Public Works and Highways (MPWH).

Function: Primary routes linking major regions and formingdirect connections between Sanaa and the

Mohafaza Centers, primary regions, and major

international border crossings.

Trip Lengths: Likely to be long and speeds relatively high.

Geometric Standards: High.


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District Centers, between National Roads and

District Centers, Secondary ports and to secondary

border crossings. Collection and distribution oftraffic between the primary and tertiary roads within

the region.

Trip Lengths: Traffic flows and trip lengths are of an intermediate

level.

Geometric Standards: Adequate geometric standards. Speeds

depend on the type of terrain.

iii. District (Tertiary) Road Network

At the District level, roads are currently under the jurisdiction of

MPWH. It is expected that the responsibility for these roads will be

transferred to the Governorate, and ultimately to the Districts when

their capacity is strengthened.

Two classes have been recommended in this category:

Distr ict Roads

Function: Provide links between Governorate Roads, and give

access from District centers to subdistricts and

between subdistricts. Roads with traffic volume

greater than 100 vehicles per day to tourist sites,

i


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The Tertiary Roads have relatively short trip lengths, serving local traffic as

their main function. A relatively low design speed is normally applicable to

local roads, especially in mountainous areas.

Rural Roads and Village Access Roads come under classes (ii) and (iii)

above.

2.2.2 RAP Roads Design Classes

International practice is to design roads according to a design speed which

varies depending on the functional class of the road and type of terrain.

However, the concept of design speed is not always appropriate as the basis

for geometric design as it can be uneconomic.

Designs should be justified economically and the optimum geometric

standards will depend on both construction and road user costs.

Construction costs will be related to the terrain and choice of pavement,

while road user costs are directly related to the volume and composition oftraffic. It is therefore recommended that the basic parameters for road

function, terrain type and traffic flow are defined initially. On the basis ofthese parameters, a design class is selected, while design speed is used only

as an index which links design class to the design parameters of sight

distance and curvature to ensure that a driver is presented with a reasonably

consistent speed environment.

RAP R d F ti l Cl ifi ti


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movement and access functions. It should be noted that in practice there are

many overlaps of functions, and clear distinctions will not always be

apparent on functional terms alone.

The design of village access roads should be based on the criterion of

achieving an appropriate level of access, and should be based on minimum

requirements of radii, width, and gradient for economic purposes.

TABLE 2.1RAPROADS FUNCTIONAL CLASSIFICATION AND DESIGN CLASSES

Road ClassDesign

Class

Traffic

Flow

(ADT)

Number

of Lanes

Surface

Type

RuralIntermedi

ate

Secondary

(Governorate)

Tertiary

(District)

A 1000-3000 2 paved

B 400-1000 2 paved


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400-1000 vehicles per day. Design to the higher Design Class would result

in an overdesigned facility during almost the whole of its life. If the initial

flow were 410 vpd, design would still be Design class B.

Types of Terrain

The following classification of terrain types is adopted:

Flat terrain Flat or gently rolling country which offers few obstacles tothe construction of a road having continuously unrestricted

horizontal and vertical alignment (transverse terrain slopemax. 5%).

Rolling terrain Rolling, hilly or foot-hill country where the slopes generally

rise and fall moderately gently and where occasional steepslopes may be encountered. It will offer some restrictions inhorizontal and vertical alignment (transverse terrain slope

5% - 20%).Mountainous

terrain

Rugged, hilly and mountainous country with river gorges.

This class of terrain imposes definite restrictions on thestandard of alignment obtainable and often involves longsteep grades and limited sight distances (transverse terrainslope more than 20%).

Escarpment

terrain

Long precipitous clifflike ridge commonly formed by

faulting. This class of terrain introduces restrictions on cross-section width, lateral clearances, and driving safety.

I l i i i h h diffi l d d f


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maximum speed that could be attained on any road is dictated by the

geometric characteristics of that road, other factors such as surface type and

drivers perception of safety play a major role in setting the design speed.As for village access, the only influencing feature is the character of the

terrain, since it is an established fact that these roads carry very low traffic

volumes, and they are treated as low cost access roads, which eliminates

the economic factor.

2.3.2 Design Speed Standards

Vertical and horizontal alignment, sight distance, and superlevation will

vary appreciably with design speed. Such features as pavement width,

shoulder width, and side clearances are usually not affected. On the other

hand, the actual speeds are determined by geometry and the quality of the

road surface.

The choice of design speed shall be a logical one with respect to the

different influencing features taking into account drivers behaviorespecially in flat terrain in Yemen. Accordingly, design speeds that are

considered on the rural intermediate roads and village access range between

20 kph in the difficult escarpments and 100-120 kph in flat areas with

good visibility. Needless to say that for some extreme stretches, the speed

may not exceed 10 kph. Table 2.1 presents proposed design speeds on

different terrain types.

TA 2 2 D S G S S O A OA S O A


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In other cases, an already acceptable rate of return may be increased

substantially by the inclusion of a short section of substandard road where

achievement of the design standard would be expensive, although the safetyimplications of this would need careful consideration.

Segments subject to speed reduction should have appropriate signing or

other warning measures. On low flow roads where most of the drivers will

be regular users, the increased risk will be less significant and the resultant

number of accidents should be negligible. Greater care and consideration

should be given to relaxations on high flow/high speed alignments.

In special circumstances, where standards have been reduced on successive

design elements, further relaxations may be made based on those reduced

approach speeds. Sight distances, and the potential accident risk as a result

of driver error, would need to be considered on a site-specific basis.

Reductions in standards should only apply to stopping distances and

curvature. Widths should not be reduced as they are particularly flowrelated, and additional widening may be required on curves with the tighter

radii (TRRL Road Note No.6).

The nature of the mountainous terrain in Yemen makes it economically

prohibitive, or often physically impossible to construct roads at the normal

standards. Thus, relaxed standards are necessary in order to ensure a cost-

effective approach to the road system. Relaxation of standards apply

i ll f d i diffi l i i d f d j


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DOCS-0974-04 2-9

TABLE 2.3DESIGN SPEED FOR RURAL ROADS BY DESIGN CLASS,TRAFFIC VOLUME AND TYPE OF TERRAIN

Road ClassDesign

ClassTraffic Flow

Number of

Lanes

Surface

Type

Design Speed (Km/h)

Flat Rolling Mountainous Escarpment

RuralIntermediate

Secondary

A 1000-3000 2 paved 120 80 40 20

(Governorate)

Tertiary

B 400-1000 2 paved 100 70 40 20

VillageAccess

(District)

C 100-400 2

paved 100 70 40 20

unpaved 80 60 30 20

Feeder

D < 100 1

paved 80 60 30 20

unpaved 60 50 30 20


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2.4 TRAFFIC

Traffic volume and composition are needed for the purpose of geometricdesign and the evaluation of economic benefits. On the other hand,

pavement design is mainly based on the magnitude of individual axle loads

and their frequency over the design life. Because the lighter vehicles have

negligible contribution to pavement damage, they may be ignored and only

the number of axle loading of the heavier vehicles need be considered.

This section covers the methodology for estimating traffic flows and

determining the esa cumulative number (see TRL Road Note 31). This

methodology is shown in Figure 2.1 below.

2.4.1 Design Life

The choice of a design period is mainly governed by budgetary

considerations, whereby in order to reduce the initial expenditures lower

design periods may be considered.

An economic analysis period of 10-20 years from the date of opening is

normally used. At the end of the analysis period the road will still have a

residual value. A pavement design life of 15 years is considered appropriate

for many road projects. At the end of the design life, the pavement will

need to be strengthened to be able to carry traffic over a further period.

h i d i i d h ld b f d i h lif


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Determine DesignLife

Survey of baseline

Traffic Flows

Traffic Forecasting

-Normal traffic

-Diverted traffic

-Generated traffic

Establishing axleloading

-Survey of axle Loads

-i i


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volumes are taken in one direction which requires care in interpreting

AADT figures.

Another estimate of daily traffic is the Average Daily Traffic (ADT)

which is defined as the total traffic in both directions over a given period

less than one year divided by the number of days in that period. The longer

the period of traffic counts the more accurate the ADT approximates

AADT, as traffic flows have daily, weekly and seasonal variations. Roads

carrying less than 1000 vehicles per day exhibit high daily variability

resulting in large errors in estimating ADT (and consequently annual traffic

flows) from traffic counts measured over a period less than one week. A

considerable decrease in the error of estimation can be realized with counts

taken over a full week. This provides traffic flow data for work days,

weekends as well as 24 hours variations. If a full week count is not

possible, there should be at least one 24-hour count on a weekday and one

during a weekend, with 16-hour counts on the other days. The 16-hours

counts are grossed up to 24-hour values in the same proportion as the 16-

hour/24 hour split (see section 2.4.7 below).

In order to account for seasonal variations several one-week counts may be

repeated, if possible, throughout the year. These automatic counts should be

supplemented by manual classification counts to obtain information on

vehicle classes.

A formal country-wide traffic data collection program should be


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Such counts can be useful as a cross check on static counts and to assess

the extent of daily or seasonal variations in traffic flow.

2.4.3 Traffic Forecasting

Three components contribute to overall traffic volumes:

i. Normal Traffic

Normal traffic is the traffic using the existing route if no pavement

were provided.

Normal traffic may be forecasted using linear time series

extrapolation of traffic levels i.e. a fixed percentage increase. If

Gross Domestic Product (GDP) forecasts are available, traffic flows

can be forecasted by relating traffic growth linearly to GDP.

ii. Diverted Traffic

Diverted traffic is the traffic that is attracted from another route to

the new road due to improved pavement.

Traffic diversion occurs when parallel routes exist. Improving an

existing road may result in diverting traffic from a shorter route

because higher speeds and level of service are available on the


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responsiveness of traffic to the decrease in transport cost accruing

from road improvement. Available data indicate that the elasticity

of demand for passenger trips is slightly greater than one, while thatfor goods is much lower.

In Section 9 of this Manual, generated traffic is defined by the

Roads Economic DecisionModel in two components:

i. Generated Traffic is the traffic attributable to decrease in

transport costs, associated with existing users of the project

road driving more frequently or driving further than before.

Generated traffic may be defined as a percentage of the

normal traffic, or by using a price elasticity of demand

which reflects the % increase in traffic per percent decrease

in transport costs.

ii. Induced Traffic is the traffic attributable to local economic

development, i.e. traffic attracted to the project due toincreased development activity in the roads zone of

influence brought about by the project. Induced traffic is

determined for each project alternative, each vehicle type

and year induced.

2.4.4 Axle Load Distribution


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1.1

1.2

1.21

1.22

1.22

1.222

1.2222

1.2 + 2.2


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The equivalence factors that are used to convert single axle loads to

equivalent standard axle is given by the relationship:

Equivalence Factor = EF =

4.5

8.16

(Tons)loadAxle

Table 2.3 shows the equivalence factors (EF) for each of the wheel loads

measured in the axle load survey. The above equation is used on all axle

loads obtained by weighing axles separately. The EF per vehicle is obtained

by adding the EFs for all axles of each vehicle. The factors for the axles aretotaled to give the equivalence factor for each of the vehicles. The mean

equivalence factor for each class or type of vehicle traveling in each

direction is then determined for all vehicles in the vehicle class whether

loaded or empty.

Table 2.3Equivalence Factors for different axle loads

Wheel load

(single & dual)(10

3kg)

Axle load(103kg) Equivalence FactorEF

1.5 3.0 0.01

2.0 4.0 0.04

2.5 5.0 0.11

3.0 6.0 0.25

3.5 7.0 0.50

4.0 8.0 0.91

4.5 9.0 1.55


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(4) Determine the mean equivalence factor for each class of vehicle and

for each direction from the results of the axle load survey (EF1i ,

EF2i).

(5) Calculate the cumulative equivalent standard axles for each

direction (T1, T2) as follows:

1i1i1 EFxVT , for direction 1 2i2i2 EFxVT , for direction 2

T, the higher of the two directional values T1, T2 should be used for

design.

Where,

T1 = Cumulative Equivalent Standard Axles for direction 1.

T2 = Cumulative Equivalent Standard Axles for direction 2.

V1i = Cumulative directional flow for class i vehicle over the design

period for direction 1.

V2i = Cumulative directional flow for class i vehicle over the design

period for direction 2.


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In order to minimize the effects of errors of estimation and forecasting, the

TRL Road Note 31 provides fixed structures for ranges of traffic as shown

in Table 4.4. As long as the estimate of T is close to the center of a range,errors are not likely to affect the pavement design. If the value of T is close

to the boundaries of the range, then sensitivity analyses should be made to

ensure that the choice of traffic classes is appropriate.

TABLE 2.4TRAFFIC CLASSESTraffic Classes Range (10

6esa)

T1 < 0.3

T2 0.30.7T3 0.71.5

T4 1.53.0

T5 3.06.0

T6 6.010

T7 1017

T8 1730

2.4.7 Example on the analysis of traffic count data

Given: A manual classified traffic count was conducted during a week in

July on a site with equal traffic flow in both directions. The data for

commercial vehicles are shown in Table A. The data for non-commercial

vehicles has already been analyzed and gave an average number of 260

vehicles per day. Information obtained from automatic traffic data recorded

over a year is shown in Table B.


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TABLE AMANUAL CLASSIFIED TRAFFIC COUNT DATA IN BOTH DIRECTIONS

HOURLY NUMBER OF COMMERCIAL VEHICLES

Time Sat Sun Mon Tue Wed Thu Fri

0:00-1:00 1 1

1:00-2:00 0 0

2:00-3:00 0 0

3:00-4:00 1 0

4:00-5:00 2 2

5:00-6:00 3 1

6:00-7:00 5 5 6 2

7:00-8:00 11 12 13 3

8:00-9:00 14 13 16 2 1

9:00-10:00 18 17 20 4 2

10:00-11:00 15 16 16 4 2

11:00-12:00 13 12 14 5 1

12:00-13:00 12 11 13 4 0

13:00-14:00 8 7 8 3 1

14:00-15:00 11 10 11 4 2

15:00-16:00 12 11 10 5 2

16:00-17:00 10 9 8 5

17:00-18:00 8 7 9 3

18:00-19:00 5 7 2


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Solution

1. Average Daily Traffic (ADT)

A = Estimated traffic count for Monday

=counthour24of00:1800:12forcount

counthour24talweekday tox

00:1800:12for

counttrafficactual

= 55 x61

158= 142

B = Estimated traffic count for Tuesday

=counthour24of00:2200:06forcount

counthour24talweekday tox

00:2200:06

forcountactual

= 146 x149

158= 155

C = Estimated traffic count for Wednesday

= 85 x76

158= 177

Average weekday traffic = (Sun + Mon + Tue + Wed) / 4

= (158 + 142 + 155 + 177) / 4


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2. Seasonal Correction Factors and AADT

The seasonal correction factors are calculated from Table B as follows:

Month ADT (CV)Seasonal Variation

Factors

Jan 145 1.05

Feb 134 0.97

Mar 132 0.95

Apr 150 1.08

Mai 161 1.16

Jun 158 1.14

Jul 125 0.90

Aug 114 0.82

Sep 120 0.86

Oct 136 0.98

Nov 145 1.05

Dec 134 0.97

Annual Mean 138 1.0

From the ADT values above, it can be seen that the July value (125) is

lower than the annual average value (138). The results from the traffic

surveys carried out in July should be adjusted upwards accordingly to give

the seasonally adjusted number.

The traffic survey was carried out in July for which the adjustment factor is


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2.4.8 Example on Calculation of Equivalence Factors

Given: Survey data for commercial vehicles shown in Table C.

Calculate: 1) EF for axle roads, 2) EF for each vehicle, 3) Average EF for

the vehicle type.

TABLE CAXLE LOAD DATA FROM SURVEY

No. TimeE=Empty

F=FullLoad Type

Axle Load (Tons)

Axle 1 Axle 2 Axle 3

1 7.05 E none 3.66 3.32 2.512 9.57 E none 2.68 4.38 2.71

3 11.36 E none 4.00 2.81 2.64

4 14.48 E none 4.20 5.46 5.45

5 14.50 E none 4.04 4.80 4.53

6 15.07 E none 4.11 3.86 2.49

7 8.10 F Gravel 4.03 6.85 6.99

8 8.14 F Gravel 5.32 13.31 13.14

9 8.55 F Bottles 4.51 6.23 4.73

10 9.21 F Gravel 6.30 12.94 14.36

11 3.36 F Gravel 6.33 15.49 15.3212 3.39 F Gravel 6.07 14.75 14.56

13 3.55 F Sand 6.50 14.56 14.24

14 3.58 F Feeds 3.93 9.54 6.00

15 10.15 F Gravel 3.80 6.09 6.18

16 10.44 F Gravel 4.52 7.09 7.63

17 10.52 F Gravel 4.26 7.17 6.88

18 10.54 F Gravel 3.80 7.45 6.05

19 14.32 F Sand 6.61 15.38 14.36


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TABLE DDATA ANALYSIS SHOWING EQUIVALENCEFACTORS

No. Time E=EmptyF=Full

LoadType

Axle Load (Tons) Equivalence Factors Total EFper

vehicleAxle 1 Axle 2 Axle 3 Axle 1 Axle 2 Axle 3

1 7.05 E none 3.66 3.32 2.51 0.027 0.017 0.005 0.050

2 9.57 E none 2.68 4.38 2.71 0.007 0.060 0.007 0.074

3 11.36 E none 4.00 2.81 2.64 0.040 0.008 0.006 0.055

4 14.48 E none 4.20 5.46 5.45 0.050 0.164 0.163 0.377

5 14.50 E none 4.04 4.80 4.53 0.042 0.092 0.071 0.205

6 15.07 E none 4.11 3.86 2.49 0.046 0.034 0.005 0.085

7 8.10 F Gravel 4.03 6.85 6.99 0.042 0.455 0.498 0.935

8 8.14 F Gravel 5.32 13.31 13.14 0.236 9.041 8.532 17.8099 8.55 F Bottles 4.51 6.23 4.73 0.069 0.297 0.086 0.452

10 9.21 F Gravel 6.30 12.94 14.36 0.312 7.963 12.723 20.999

11 3.36 F Gravel 6.33 15.49 15.32 0.319 17.891 17.024 35.233

12 3.39 F Gravel 6.07 14.75 14.56 0.264 14.354 13.540 28.158

13 3.55 F Sand 6.50 14.56 14.24 0.359 13.540 12.251 26.151

14 3.58 F Feeds 3.93 9.54 6.00 0.037 2.020 0.251 2.308

15 10.15 F Gravel 3.80 6.09 6.18 0.032 0.268 0.286 0.586

16 10.44 F Gravel 4.52 7.09 7.63 0.070 0.722 0.733 1.031

17 10.52 F Gravel 4.26 7.17 6.88 0.054 0.559 0.464 1.078

18 10.54 F Gravel 3.80 7.45 6.05 0.032 0.664 0.260 0.956

19 14.32 F Sand 6.61 15.38 14.36 0.388 17.225 12.723 30.335

20 14.38 F Gravel 5.87 13.92 11.64 0.227 11.060 4.945 16.233

21 14.45 F Sand 6.00 13.61 11.55 0.251 9.994 4.775 15.020

22 15.19 F Sand 6.33 16.13 13.43 0.319 21.466 9.413 31.198

23 15.50 F Fertilizer 6.44 12.53 7.62 0.345 6.889 0.735 7.969

2. Calculating EF for each vehicle


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2.4.9 Example on Calculation of Cumulative Equivalent Standard Axles

The result of an axle load survey on a road section for various truck typesand their annual growth rates are as follows:

Truck Type Axle CodeADT one

direction

Mean EF for

the Vehicle

Type

Annual

Growth Rate

(i)

Medium Trucks 2 axlesGW < 11.5 Tons

1.2 94 0.68 6%

Heavy Trucks 2 axles

GW > 11.5 Tons1.2 58 4.80 5%


GW > 11.5 Tons1.22 17 10.34 3%

Heavy Truck - trailer

4 axles1.222 9 8.85 3%

Calculate the average annual numbers of equivalent standard axles for the

current year for each truck type. Assuming the road section to be repaved

during the current year, calculate the cumulative equivalent standard axlesfor a design life for the pavement of 15 years, and determine accordingly

the appropriate traffic class for pavement design.

Solution:

1. Calculate the average daily esa in the current year:


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DOCS-0974-04 2-25

TABLE EDETERMINATION OF CUMULATIVE EQUIVALENT STANDARD AXLES

Truck Type ADT (one direction) EF Average Daily esaesa current year

(103esa)

15-yr Cumulative

Factor

Cumulative esa for 15

years (106esa)

Medium Trucks 2 axlesGW > 11.5 Tons 94 0.68 64 23.36 23.28 0.54


GW > 11.5 Tons 65 4.80 312 113.88 21.59 2.46


GW > 11.5 Tons 17 10.34 176 64.24 18.6 1.20

Heavy Truck - trailer4 axles 9 8.85 80 29.20 18.6 0.54

T = 4.77


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SECTION 3

GEOMETRIC STANDARDS

Section

3


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Section 3Geometric Standards

Republic of Yemen


SECTION 3

GEOMETRIC STANDARDS

TABLE OF CONTENTS

Page

3.1 Introduction 13.2 Sight Distance 13.2.1 Stopping Sight Distance 13.2.2 Intermediate Site Distance 33.3 Superelevation 33.4 Horizontal Alignment 73.4.1 Circular Curves 73.4.2 Transition Curves 83.4.3 Improving Horizontal Alignment 103.4.4 Geometric Controls 10


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SECTION 3

GEOMETRIC STANDARDS

3.1 INTRODUCTION

As mentioned in Section 2, the geometric features for most of the rural

roads in Yemen are governed by the natural terrain characteristics.

However, this does not exclude the fact that the geometric design should be

consistent with the traffic volume, composition of traffic and design speed.This Section provides a summary of the geometric design data and contains

sufficient information for the majority of roadway design problems. A

Policy on Geometric Design for Highways and Streets by the American

Association of State Highways and Transportation Officials (AASHTO) is

a reference in which the basic theory behind geometric design data is fully

explained. Also, Guidelines for Geometric Design of Very Low-Volume

Roads (ADT 400)by AASHTO, and TRRL Road Note No. 6 A guide

to Geometric Design can be consulted.

Several design standards from projects previously undertaken in Yemen

have been reviewed. The Consultants have taken into consideration the

technical aspect combined with the specific requirements of this project in

developing a new set of geometric standards. The review covers the sight

distance, horizontal and vertical alignment and cross sectional elements as


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Stopping sight distance is generally determined as the sum of two

distances:

(1) Reaction Distance, the distance traveled by the vehicle from the

instant the driver sights an object necessitating a stop to the instant

the driver actually applies the brakes. This distance depends on the

reaction time of the driver which varies according to the alertness of

the driver. AASHTO Policy on Geometric Design for Highways

and Streets uses a brake reaction time of 2.5s, while AASHTO

Guidelines for Geometric Design of Low-Volume Local Roads

(ADT 400) recommends a reaction time of 2s for rural roads.

(2) Braking Distance, the distance required to stop the vehicle from

the instant the brakes are applied. This distance is a function of the

longitudinal friction factor, and thus deceleration of the vehicle.

The stopping sight distance in the AASHTO Policy is given by the

following formula which has two components corresponding to the twodistances mentioned above:

a

V039.0Vt278.0S

2

where,

S = stopping sight distance, m

t = brake reaction time, s


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As discussed in Section 3.5.2, sight distance plays a key role in determining

the minimum lengths of crest vertical curves. Stopping sight distance is

measured from the drivers eyes (eye height, h1) to an object height (h2).AASHTO policy uses h1= 1080 mm and h2= 150mm or h2= 600mm if the

object is a vehicle. With the increased use of SUVs, the average eye height

has increased, so that h1could be assumed to be 1.4m and h215cm. This

sight distance criterion should be checked for all classes of roads irrelevant

of the number of lanes, traffic volume or pavement type. Measures to be

taken to correct any deficiency include removal of obstacles, excavation of

side slopes or trimming of sharp crest curves.

3.2.2 Intermediate Site Distance

The Intermediate sight distance is the distance needed for two drivers

traveling with design speed to stop before colliding. This criterion is valid

in the case of one-lane roads. For village access roads having a traffic load

of less than 50 vehicles/day the intermediate sight distance can be neglected

if the lane is widened up to at least 4.5m.

Table 3.2 shows the proposed minimum normal and relaxed standards for

sight distances related to design speeds for RAP roads.

Table 3.2: Minimum Standards for Sight Distances Related to Design Speeds

Design

Speed,

Minimum Sight Distance, m

Stopping Intermediate


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Superelevation may be defined as the rotation of the roadway cross section

in such a manner as to overcome the centrifugal force that acts on a motor

vehicle traversing a curve. On a superelevated carriageway, the centrifugalforce is resisted by:

1. The weight component of the vehicle parallel to the superelevated

surface and

2. The side friction between the tires and the pavement.

It is impossible to balance centrifugal force by superelevation alone,

because for any given curve radius, a certain superelevation rate is exactlycorrect for only one operating speed around the curve. At all other speeds,

there will be a side thrust outward or inward relative to the center of the

curve, which must be offset by side friction.

The general formula to calculate superelevation for various curve radii is

the following:

e+f = V

2

/ 127Rwhere,

e = Superelevation rate, in meter per meter width of road.

f = side friction factor or coefficient of side friction between vehicle tires

and road pavement.

R = radius of curve, in meters.

V = design speed in kph.


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Superelevation slopes on curves shall extend the full width of the

shoulders, except that the shoulder slope on the low side shall not be less

than the minimum shoulder slope used on tangents.

For 2-lane roadways, different superelevation slopes for each half of the

road shall not be used; superelevation shall remain a plane for the full width

of roadbed, except on transitions.

The axis of rotation for superelevation is usually the centerline of the road.

However, in special cases such as desert roads where curves are preceded

by relatively long tangents, the plane of the superelevation may be rotatedabout the inside edge of pavement to improve perception of the curve. In

level country, drainage pockets caused by superelevation may be avoided

by changing the axis of rotation from the centerline to the inside edge of the

pavement.

Superelevation transition is the general term denoting the length of

highway needed to accomplish the change in cross slope from a normalcrown section to the fully superelevated section, or vice versa. To meet the

requirements of comfort and safety the superelevation run-off should be

effected uniformly over a length adequate for the likely travel speed. The

superelevation transition can be divided into two sections defined as

follows:

- Tangent Run-off or Run-out: This is the distance in which the level


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DOCS-0974-04 3-6

Figure 3.1Typical Details for Superelevation Runoff

Inside Edge of

Roadway (P.G.L)

Outside Edge of

Roadway

1 / 4 LA

or 10m Max

Tangent Run out Length of Superelevation Runoff

Length of Application (as shown on the profile)

Total Length of Application

1 / 4 LA

or 10m Max

or 10m Maxor 10m Max

Inside Edge of

Roadway (P.G.L)

Outside Edge of

Roadway1 / 4 LA

or 10m Max 1 / 4 LA

or 10m Max


Outside Edge of

Roadway

Superelevation Application Details LA

+e

+eo

-eo

-e

+e

+eo

-eo

-e

B

B/2e

B/2e

B/2e2

B/2e2

B/2e

B/2e

+e

-eo

-e

+e

+eo

-e

P G L C/L

B/2e2

B/2e2

Sign Convention for CrossfallMethod of Attaining Superlevation of

Pavement Revolved aboutCenterlines of Roadways

e

e

Inside Edge of

Roadway (P.G.L)

Outside Edge of

Roadway

1 / 4 LA

or 10m Max

Tangent Run out Length of Superelevation Runoff

Length of Application (as shown on the profile)


1 / 4 LA

or 10m Max

or 10m Maxor 10m Max

Inside Edge of

Roadway (P.G.L)

Outside Edge of

Roadway1 / 4 LA

or 10m Max 1 / 4 LA

or 10m Max


Outside Edge of

Roadway

Superelevation Application Details LA

+e

+eo

-eo

-e

+e

+eo

-eo

-e

B

B/2e

B/2e

B/2e2

B/2e2

B/2e

B/2e

+e

-eo

-e

+e

+eo

-e

P G L C/L

B/2e2

B/2e2

Sign Convention for CrossfallMethod of Attaining Superlevation of

Pavement Revolved aboutCenterlines of Roadways

e

e


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3.4 HORIZONTAL ALIGNMENT

3.4.1 Circular Curves

The natural terrain, as mentioned earlier, governs the horizontal alignments.

The roads that are located on escarpments are therefore characterized by the

multitude of hairpin curves that necessitate a back and forth maneuver in

order to make the turn. For these roads, no minimum curvature can be

specified, as speeds will drop to zero during the maneuver.

For the remaining cases, the minimum radii will have to correspond to thedesign speeds as per the recommendations listed in Table 3.4, determined

using the superelevation equation defined above:

R =f)(e127

V2

Table 3.4: Horizontal Curve Design DataMinimum Radii (m)

Design

Speed

kph

fmax

Rural Intermediate Roads Village

Access

Roads

emax= 6%

Flat/Rolling

emax= 8%

Mountainous

emax= 6%

Escarpment

emax=4% emax =6%

20 0.18 - 15(1)

15(1)

15(1)

15

30 0.17 - 30 35 30 30


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Design Speed, Kph 30 40 50 60 70 85 100 120

Side Friction Factor 0.33 0.30 0.25 0.23 0.20 0.18 0.15 0.15

The values for horizontal curve design shown in Table 3.4 should be used

for rural roads when practical. In constrained situations relaxed values

based on reduced design speed shown in Table (3.5) may be used.

In cases where the existing curve has a radius less than those listed, and

widening entails land acquisition, high excavations or high fills, signs shall

be posted to reduce the speed to correspond to the adopted radius.

Table (3.5) Horizontal Curve Design Data Minimum Radii (m)

for Reduced Design Speed

Design

Speed

kph

Reduced

Design

Speed

kph

fmax

Rural Intermediate Roads Village

Access

RoadsFlat / Rolling Mountainous Escarpment

emax= 8%

emax= 6% emax= 4% emax= 6% emax= 6%

20 20 0.180 __ 15(1) 15(1) 15(1) 15

30 25 0.170__

20 25 20 20

40 30 0.170 30 30 35 30 30

50 40 0.170 50 55 60 55 55

60 50 0.160 80 90 100 90 90


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Several methods exist for the calculation of transition curves and may be

used in most situations. The rate of pavement rotation methodhas been

adopted here. The rate of pavement rotation is defined as the change incrossfall divided by the time taken to travel along the length of transition at

the design speed. The length of transition curve is derived from the

formula:

3.6n

V.eLs

where Ls= Length of transition curve (meters)

e = Superelevation of the curve (meters per meter)V = Design speed (km/h)

N = Rate of pavement rotation (meters per meter per second)

The same values of rate of change of pavement rotation should be used to

calculate the minimum length (Lc) over which adverse camber should be

removed on a tangent section prior to the transition:

3.6n

V.eL nc

where Lc= Length of section over which adverse camber is removed

(meters)

en= Normal crossfall of the pavement (meters per meter).


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3.4.3 Improving Horizontal Alignment

The major criteria for considering improvements to the horizontalalignment are the following:

1. Safety

2. Grade profile

3. Type of Roadway

4. Design speed

5. Topography

6. Cost (Construction, Maintenance, Operation)

Of these considerations, safety comes first. Therefore, the stopping sight

distance shall be adequate at all points of the roadway.

The grade profile shall be considered next in mountainous and escarpment

section. Critical grades are commonly encountered on existing roads

located in these sections. The possible improvement of these grades byadjusting the horizontal alignment should be investigated in the cases

where such an adjustment does not entail major earthworks or

encroachment into private property.

The road types that are considered in this Manual are the rural intermediate

roads and the village access roads. The standards for the horizontal

alignment will vary for each of these two road types.


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Curve Length and Central Angle:Winding alignment composed of short

curves shall be avoided since it results in erratic operation. In general, the

length of curve should be at least 100 m long for a central angle of 5degrees. The minimum length shall be increased 30m for each 1 degree

decrease in the central angle. Sight distance or other safety considerations

shall not be sacrificed thereby. In general, the central angle of each curve

shall be as small as physical conditions permit, in order to achieve the

shortest possible route.

Tangents or Straights Aff ording Passing Opportun ities: An 800m tangent

is considered adequate for the purpose of providing passing opportunitieson 2-lane roadways. Passing tangents shall be provided as frequently as

possible in keeping with the terrain. Shorter radii ensuring greater length of

intervening tangent shall be preferred to sweeping curves of large radii

which reduce the length of intervening tangents. However, sharp curves at

the end of passing tangents and especially long tangents shall not be used.

Compound Cur ves: These shall be avoided in general. On a compound

curve the shorter radius shall be least 2/3 of the longer radius. The total arc

length of a compound curve shall not be less than 100m.

Curvature on Fi ll s:Other than flat curvature should be avoided on high,

long fills. In the absence of cut slopes, shrubs, trees, etc., above the

roadway, it is difficult for drivers to perceive the extent of curvature and

adjust their operation to the conditions.


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applied on the inside edge of pavement only, and preferably attained over

superelevation runoff length. Widening values are given in Table 3.5.

Figure 3.2 shows how carriageway widening on curves is gradually

attained from the inside of the curve.

Table 3.7: Horizontal Curve Design Data

Widening on Curves for all Road Types

Radius Pavement Widths, m

4.0-4.9 5.0-5.9 6.0-6.9 7.0


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curvature design standards for such alignments are to be reduced to the

minimum in order to avoid land acquisition.

The major criteria for considering improvements to the vertical alignment

are the following:

1. The grade line is a reference line by which the elevation of the

pavement and other features of the highway are established. Though

controlled mainly by the topography, other factors such as horizontal

alignment, safety, sight distance, speed, construction costs and the

performance of heavy vehicles on a grade should be considered.

2. All portions of the grade line shall meet sight distance requirements for

the design speed classification of the road.

3. In level terrain, the elevation of the grade line is often controlled by

drainage considerations. In rolling terrain a reasonably undulating

grade line is desirable from the standpoint of operation and

construction economy.

4. Two vertical curves in the same direction separated by a short section

of tangent grade shall in general be avoided, particularly in valley

curves.

5. It is desirable to reduce the grades at intersections. Turns are


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2

L

x

200

L.Gy

where y = vertical distance from the tangent to the curve (meters)

x = horizontal distance from the start of the vertical curve

(meters)

G = algebraic difference in gradients (%)

L = length of vertical curve (meters)

3.5.2 Crest Curves

The provision of ample sight distance for the road design speed represent

the main control for safe operation on crest curves.

The minimum lengths of crest curves are designed to provide sufficient

sight distance during daylight conditions. Conditions normally do not allow

full overtaking sight distance and the design should aim to reduce thelength of crest curves to provide minimum stopping sight distance in order

to allow for increasing overtaking opportunities on the gradients on either

side of the curve.

Two conditions exist when considering minimum sight distance criteria on

vertical curves. The first is where sight distance is less than the length of

the vertical curve, and the second is where sight distance extends beyond


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Tables 3.8 and 3.11 show the two vertical alignment design parameters for

various terrain types: minimum vertical curvature in terms of K-values, and

maximum gradient.

Table 3.8 shows the minimum K-values for the following conditions using

the equations above:

1. Stopping sight distance measured from eye height h1of 1.080m to a

stopped vehicle, i.e. object height h2 = 0.6m. K-values are for

ADT


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Table 3.8Minimum Vertical Curvature Values

for Very-Low Volume Roads

(1) K-values are for higher risk locations for ADT 100-250 vpd and all locations for

250-400 vpd. K-values are for H1= 1080 mm and h2= 600 mm representing a stopped

vehicle.

(2) K-values are based on stopping sight distance measured from eye height of 1.05m and

an object height of 0.2m.

Design

Speed

(Kph)

AASHTO ADT


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access roads. No-passing signs should be erected where the available sight

distance does not allow overtaking.

3.5.3 Sag Curves

It has been assumed that adequate sight distance will be available on sag

curves in daylight. However, at night, visibility is limited by the distance

illuminated by the headlamp beams, and minimum sag curve length for this

condition is given as:

For S < L: tan.200.

1

2

Sh

SG

Lm

For S > L:

G

ShLm

tan.200 1

Where h1= headlight height (meters)

= angle of upward divergence of headlight beam (degrees)

Appropriate values for h1and are 0.6 meters and 1.0 degrees respectively.

The use of these equations can lead to requirements for unrealistically long

vertical curves as, especially at higher speeds, sight distances may be in

excess of the effective range of the headlamp beam, particularly when low

meeting beams are used. Thus, the only likely situation when the above


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For very low levels of traffic flow with only a few four-wheel drive

vehicles, the maximum traversable gradient is in excess of 20 per cent.

Small commercial vehicles can usually negotiate a 19 per cent gradient,whilst two-wheel drive trucks can successfully tackle gradients of 15-16

per cent except when heavily laden.

Gradients of 10 per cent or over will usually need to be paved to enable

sufficient traction to be achieved, as well as for pavement maintenance

reasons.

As traffic flows increase, the economic disbenefits of more severegradients, measured as increased vehicle operating and travel time costs,

are more likely to result in economic justification for reducing the severity

and/or length of a gradient. On the higher design classes of road, the lower

maximum recommended gradients reflect the economics, as well as the

need to avoid the build up of local congestion. However, separate economic

assessment of alternatives to long or severe gradients should be undertaken

where possible or necessary.

Table 3.11: Vertical Alignment Data Maximum Gradient

Design Speed

Kph

Gradient, %

Rural Intermediate RoadsVillage Access

Flat/Rolling Mountainous Escarpment

20 - 14(1)

15(2)

15(3)

30 - 11 11 11


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journey times and reduced vehicle operating costs. Benefits will increase

with increases in gradient, length of gradient, traffic flow, the proportion of

trucks, and in overtaking opportunities. The effect of a climbing lane inbreaking up queues of vehicles held up by a slow moving truck will

continue for some distance along the road.

Experience has shown that climbing lanes are unlikely to be justified other

than on a small proportion of roads with heavy flows.

As climbing lanes will be used largely by trucks and buses, they must be a

minimum of 3.0 meters in width. They must be clearly marked and, wherepossible, should end on level or downhill sections where speed differences

between different classes of vehicles are lowest to allow safe and efficient

merging manoeuvres.

3.6 CROSS SECTION

3.6.1 Rationale for Determining Road Widths

The cross section of a roadway is made up of:

Number and width of lanes

Shoulder width

Cross slopes


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Road class D: Village Access Roads with low volume of traffic (1000

vpd): a running surface width of 6 7m allows vehicles in opposing

directions to pass safely without the need to slow down or move laterally in

their lanes.

Economic considerations call for minimization of road width in order to

reduce construction and maintenance costs, whilst being sufficient to carry

the traffic flows efficiently and safely.

Table 3.12 shows the recommended values for carriageway, shoulder and

formation widths for various classes of roads.

Figure 3.1 shows typical road cross section with dimension ranges.

Rural Roads - Design ManualRepublic of Yemen


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g


pMinistry of Public Works and Highways

DOCS-0974-04 3-21

Table 3.12Summary of Standards for Various Cross Section Elements

Road Function

ApproxRange of

Traffic Flow

(ADT)

No. of LanesLane width

(m)

C/W width

(m)

Shoulder width

(m)

Cross Slopes (% )

Pavement Shoulders Formation

Rural Intermediate(Governorate)

400-3000 2 3.0-3.5 6-7 0.0-1.5 2.0% 2-3% 2-3%

Tertiary

(District)100-1000 2 2.5-3.0 5-6 0.0-1.0 2.0% 2-3% 2-3%

Feeder(Village Access)


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pMinistry of Public Works and Highways

DOCS-0974-04 3-22

ROAD MARKING

2-3%

2-3% 2-3%

2-3%

2%2%

FORMATION WIDTH

6 - 8

1 LANE1 LANE

2.5 3.5 2.5 3.5 0.5 1.50.5 1.5

CARRIAGEWAYGRAVEL

SHOULDERGRAVEL

SHOULDER

C

L

Min0.5

1.0

ALL DIMENSIONS ARE IN METERS

Crossfall

Figure 3.3 Typical Cross Section Terminology and Dimensions

Slope normally

1V:2H for depth

of 2m, or in

accordance with

type of soil and

depth

Slope

according to

type of soil and

depth of Cut.

For existing

alignments a

slope of 1:10may be used

Drainage ditch

usually V-shaped.

Other shapes mayalso be used.

Surfacing

Base

Subgrade


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The shoulder widths depend upon the availability of Right-of-Way, type of

terrain and the type of the road base (bound or unbound). These are

observed to fall in the range of 0 to 2 meters. No paving is generally neededfor shoulders except in locations where water is likely to penetrate at the

edge of the pavement which is an area particularly vulnerable to structural

damage. Shoulders should also be paved if the level of traffic flow

approaches the upper limit for a particular design class. In such cases a

surface dressing or other seal may be applied.

For 2-lane paved roads with carriageway width greater than 5 meters, full

shoulders may be omitted in mountainous and escarpment type terrainwhere the costs of achieving desired cross sections are very high. In this

case the minimum paved width shall be 5.5 meters and side drains and edge

barriers should be given special considerations.

For single lane roads the carriageway width shall be 3.0m. Shoulders

widths may be 0-1.5m depending on traffic volume, mix and terrain.

Two lane roads should be delineated by continuous lines at least 10cm wide

situated on the shoulder immediately adjacent to the running surface.

Centerline markings are also recommended on roads of at least 5m width.

3.6.3 Cross Slope

Cross slope (crossfall) is needed on all roads to assist in the draining of


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the excavation of ditches on tracks through steep sidelong ground. In such

cases drainage details should be provided. Figure 3.4 shows this concept

with is advantages and disadvantages. Drainage channel shape and slope ofcutting are determined according to soil and terrain types.

Side Slopes

V1 V2Sound Rock Weathered Rock Sity Sand H


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places and the potential difficulty of reversing. In general, passing places

should be constructed at the most economic locations as determined by

terrain and ground condition, such as at transitions from cut to fill, ratherthan at precise intervals.

The length of individual passing places will vary with local conditions and

the sizes of vehicles in common use but, generally, a length of 20 meters

including tapers will cater for most commercial vehicles on roads of this

type.

A clear distinction should be drawn between, passing places and lay-bys.Lay-bys may be provided for specific purposes, such as parking or bus

stops, and allow vehicles to stop safety without impeding through traffic


S 3 G S d d

Republic of YemenMi i f P bli W k d Hi h


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Section 3Geometric StandardsMinistry of Public Works and Highways

DOCS-0974-04 3-26

Cross-Section with Cross-fall to Valley Side Cross-Section with Cross-fall to Mountain Side

Advantages Disadvantages Advantages Disadvantages

- no side drains required, resulting insubstantial reduction in earthworks.

- less cross-drainage structures required

- evenly spread surface water runoff alongroad edge reduces erosion problems.

- potentially dangerous for vehicles slidingwhen surface slippery

- careful maintenance of surface required toensure water drains evenly over shoulders

- when gradient exceeds 8 percent, cross-fallmust be changed to mountain side.

- safer for vehicles in wet and slipperyconditions

- wider formation improves sight distance

- critical outside edge of road less prone todamage

- controlled surface drainage outlets

- more earthworks because of the increasedwidth to accommodate drainage.

- higher back slopes requiring protection.

- frequent cross-drainage structures required

- more expensive

Source: WB Technical Paper 496.

Figure 3.5Alternative Cross Sections in Mountainous Terrain

Shoulder

50 - 100

C

L

Carriageway200-250

Catch water drains where

required; masonry lined

channel and/or polythene

sheet to avoid water from

seeping into slope material

Drain

60 - 80

3% - 5%

In situ soil or

optional gravel

Bio-engineering

slope protection on

slopes below and

above road

Side drain: in weak

material to be

masonry linedNote: cut and fill to balance, avoid

spoil as much as possible

Construction steps: to allow for careful

excavation with minimal disturbance of

natural slope and regular, well compactedfill layers on stable ground


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SECTION 4

EARTHWORKS AND PAVEMENT

Section

4


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Section 4 - Earthworks and Pavement

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SECTION 4


TABLE OF CONTENTS

Page

4.1 General Definitions 14.1.1 Subgrade 14.1.2

Base 1

4.1.3 Surfacing 14.1.4 Pavement Section 24.2 Earthworks 44.2.1 Geotechnical Surveys 44.2.2 Borrow Pits & Dump Sites Location 44.2.3 Sand Dune Areas 74.2.4 Excavation 84.2.5 Embankments 94.3 Subgrade 104.3.1 General 104.3.2 Classes of Subgrade Bearing Strength 104.3.3 Improved Subgrade 114.4 Pavement Materials 11


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SECTION 4


4.1 GENERAL DEFINITIONS

4.1.1 Subgrade

- Subgrade is all the material below the pavement and may include

in-situ material, fill and improved subgrade. For assessing anysection of subgrade the average CBR should be at least equal to the

median for the category selected, and no CBR value should fall

below the lowest value in the range. When subgrade CBR is below

30% it is to be replaced by suitable material with CBR more than

30% for a thickness of 20cm.

- Improved Subgrade is a granular capping layer of selected fill

material, the top of which is at formation level, placed where thenatural in-situ or fill material is unsuitable for the direct support of

the pavement.

- Formation is the surface of the ground, in its final shape, upon

which the pavement structure, consisting of base and surfacing is

constructed.


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- Bituminous Binders are petroleum-derived adhesives used to stick

chippings on to a road surface, in surface dressings or to bind

together a layer of asphalt concrete wearing course.

- Cutback Bitumenis a bitumen whose viscosity has been reduced by

the addition of a volatile diluent.

- Bitumen Emulsionis a binder in which petroleum bitumen, in finely

divided droplets, is dispersed in water by means of an emulsifying

agent to form a stable mixture.

- Prime Coatis an application of low viscosity bituminous binder to

an absorbent surface, usually the top of the base. Its purposes are to

waterproof the surface being sprayed and to help bind it to theoverlaying bituminous course.

- Tack Coat is a light application of bituminous binder to a

bituminous or concrete surface to provide a bond between this

surface and the overlaying bituminous course.

4.1.4 Pavement Section

There are four types of pavement that can be used for rural intermediate

roads and village access roads:

1a. Flexible Asphalt Concrete Pavement Section comprises a 40mm

thick layer of asphaltic concrete on top of high quality crushed

aggregate base course layer or crushed natural granular material. Its

use is economically justified only for the high traffic categories and


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20cm

If subgrade strength (CBR) is 30% for 20cm.

Bituminous Surface

Dressing

Fractured rock granular

Base Course

In-situ Material or

Selected Fill

Formation

Subgrade

Pavement

Asphalt ConcreteSurfacing


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4.2 EARTHWORKS

4.2.1 Geotechnical Surveys

Geotechnical surveys are carried out at three stages in the project

preparation process at increasing levels of detail: 1) identification, 2)

feasibility and 3) design.

For new roads geotechnical surveys are conducted to select and compare

alternative routes for the road. Information is obtained on the supportingground for the road, earthworks, bridge sites, drainage, materials and water

for construction.

For upgrading and reconstruction works, geotechnical information is

needed to determine the choice and properties of materials that are

available for use in pavement construction.

For route location, the principal terrain related factors include(1):

- Subgrade strength, or present instability problems.

- Materials used in construction.

- Earthworks (cuttings and embankments).

- Surface and subsurface drainage.

- The need for structures.





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Section 4 a thwo ks and avementy g y

DOCS-0974-04 4-5

TABLE 4.1STEPS OF THE GEOTECHNICAL SURVEY PROCESS BY PROJECT PREPARATION STAGE

Project Preparation Stage Purpose and Means Information Sought

1. Identification

Reconnaissance Stage

To identify possible alternative routes in terms of corridors

using:

- maps- satellite images 1:25,0001:500,000 (if necessary)- air photo mosaics 1:100,000

Boundaries between terrain types and changes in topography, geology,

drainage pattern, vegetation and land use, with consideration to:

- courses of major rivers- catchment areas of major river systems- extent of flooding of low-lying areas- possible sources of water for construction- possible sources of construction materials- pattern of regional instability- extent of erosion- spread of deforestation- assessment of land acquisition/site clearance problems- location of all possible bridge sites.

2. Feasibility To carry out an appraisal of the corridors in order to select thebest route using:

1. air photos: 1:20,000 1:60,000 supplemented, if necessary,by color information from satellite images.

2. site investigations of alternative routes to note key physicaland geotechnical features.

3. selected lab tests.4. cost comparison of alternative alignments.

Following items to be investigated:

- foundation conditions-

catchment areas and the location of culverts- location of spoil areas and possible borrow areas- possible sources of construction materials- identification of most favourable bridge sites- possible major hazard areas such as poorly drained soils, spring lines,

unstable areas, erosion in river courses.

3. Design for implementation Detailed field studies of the selected route with detailed airphoto interpretation to help plan a comprehensive site

investigation with full sampling and testing program.

Testing program should include:

- construction materials- subgrade conditions- cuttings and embankments- areas of instability- erosion and soft ground- requirements for frequency and size of culverts- bridge sites

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In addition, the selection of dumping sites depends on the type of dumped

material with respect to the site material. It should be kept in mind that if

the dumped material contains contaminated substances, it should be

dumped away from any ground water recharges areas and other

environmental factors should be accounted for. Furthermore, the effect of

the bulk volume and weight of the dumped stock pile should be studied in

such a way as not to impose failure of below strata due to gravity.

Due to the excavation works, an instability status may develop causing

local or global failures that influence the surroundings. These problems

may be avoided if a prior assessment of the existing ground conditions isperformed; this covers an assessment of the rock discontinuities and/or soil

parameters. Moreover, environmental impact assessment and hydro-

geological studies should be performed to avoid any damage to nature or

water recharge areas.

In line with the above, the following steps shall be carried out for

identifying borrow areas and dump sites:

1. Site topographical survey to determine the boundary limits of the

proposed site and the estimated quantities.

2. Visual inspection of in-place conditions to give the minimum

possible safe distance between the borrow area boundary and

surrounding sites, for example archeological site, natural resources,

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4.2.3 Sand Dune Areas

All roads in sand dune areas require careful investigation to ensure that the

accumulation of sand is minimized and does not provide a hazard to the

road user. It is important that the alignment is selected after careful

consideration of the wind direction. If at all possible, roads should be

elevated on embankments above general dune crest height and cuts and all

features causing wind speed to drop and sand deposition to occur should be

avoided.

In areas of varying wind direction and where considerable dune movementis occurring, extreme difficulty can be encountered in construction and

maintaining any type of road.

In dune areas, the availability of materials for road construction is usually

severely limited and the need to import material, often for considerable

distances should always be considered.

The following considerations should be used to select alignments intransverse and longitudinal sand dune areas:

If the road is parallel or inclined to dune but perpendicular to theprevailing wind direction, few problems are usually encountered. The

road should be constructed in the interdune spaces keeping away from

the leeward side of any dunes. If two transverse sand dunes are



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Another possibility in transversing transverse dunes is to join thecrests of the dunes rather than cutting dunes. Stable slopes of one in

six need to be provided.

Road alignment in the wind direction poses few problems and caneasily follow the line of interdune plain in the case of sand dunes.

However, in the case of several longitudinal sand dunes being located

adjacent to each other, the alignment should be located on the dune

lee slope since this requires minimum cut and fill.

Roads perpendicular to wind direction (or parallel to longitudinaldunes) or inclined to it, pose serious problems, since the prevailingwind direction is similar to that of the axes of the dunes. Cuttings and

embankments can be subjected to serious sand drift and erosion.

Valleys or saddles in a chain of longitudinal sand dunes can be safelyutilized for aligning the road. The alignment of the road will often

become circuitous by following the interdune spaces but will be the

best from construction and maintenance points of view.

4.2.4 Excavation

General

Wherever a cutting is required, consideration needs to be given to the

following factors that will affect its design and cost:



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- Clay 3V:1H- Weathered rock 4V:1H- Sound rock 6V:1H (in existing alignments it

can be relaxed to 10:1)

In the following situations, analytical slope stability appraisals shall be

performed based on parameters obtained through detailed site investigation

and associated laboratory testing:

- Jointed rock conditions- Problematic material- Water table situations- Cutting depth exceeding 8 meters(ii ) Other Factors

Partly for aesthetic and safety reasons a low angle slope is normally

considered more desirable than a near vertical one, even if other factors will

allow this latter course. The need for, or the surplus of fill material, willalso have an influence on slope angles.

In deep cuttings, where the pavement is laid shortly after completion of the

cutting, consideration should be given to heave.

Guidance on satisfactory slope angles from the points of view of both

Rural Roads Design ManualRepublic of Yemen


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