kenya-road-design-manual-for highway and expressway design

kenya-road-design-manual-for highway and expressway design

1. ROAD DESIGN MANUAL

cora

sl PART 1: GEOMETRIC DESIGN OF RURAL ROADS.
| rae

capes ı - onmaat

i introduction 1
12 Units of Measurement 1
La Definitions ang Abbreviations Y

CHAPTER 2 THE ROAD SISTER

1 General 2.1
2 Road Classification 22
2. Control of Access, 23
4 Toad Reserves 25

ower

3 = DESIGN CONTROLS AND CRITERIA

Generar

Tepegraghy, Lane Use and Physical Features
Envivorsental consizerations

Rood Safety Considerations

nd Function and Level of Access Control
raffle Volume and Capacity

Jetign speed ard Other speed Controls
Design venicies

Peonoaic Consizerations

axes 4 - THE CROSS-SECTION

CHAPTER 4 - THE CROSS-SECTION
Staniard Cross-sections
Fide pitches and cut-off Ditches
Si General

2 expected Flow in Site Dité
À Enpacity of Side Divenes

Scour Protection
Econoatce and Aesthetics

ve Pavement widening

CHAPTER $ = DE Acton

General 5
Sight Distarce A
SO Stopping signe Distance 5
Meeting Sight Distance 5

5

s

À Passing Sight Distance
5 Control of Sight Distance

2. ROAD DESIGN MANUAL

PART1: GEOMETRIC DESIGN OF RURAL ROADS

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5. postacntal Asignar se
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533 the monter curve Ste
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bamos u.
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Sanction ds
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en Design Speed A
Ton mayor was €
SSrety and Operational center 64
sado pe
aay AA
ea Len benign Procedure ee
ote Eleccion es
Siete dunctior Lane and
nue en
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Altona of the major Road E
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Er eae
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Beck Regeemente ch
Entre eb

3. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

Correos Page (444)

Page
CHAPTER 7 - GRADE SEPARATED JUNCTIONS

a General za
22 Choice of Schene 72
53 Gronetrie Standards 73
7.3.2 Design speed 73
7.32 Visibility 73
71313 Acceleration and Deceleration
Lanes 73
7.3.4 Horizontal Curves and Super-
elevation 13
Vertical Curves ra
Kidthe of Slip Roads ve
Gradients 74
Chearances 74
74 yp Principles Ys
75 Types of Junction 76
CHAPTER @ - ROAD FURNITURE
ea ea
82 na
e 85
ea Marker Posts 84
es Safety Fences 85
8e Other Fences and Gates 87
87 Traffic Signe and Road Markings ee

APPENDIX 1 = DEFINITIONS

4. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

pren ı

En =

‘The standard unite of measurement to be used are bared on the

International System (SI) unite,

However, the units applicable to

road design also include some unite which are not strictly part of

multiples and sub-eultipler of SI unite are formed either by the

use of indices or prefixes.

are given in Table 1.2.1.

Definitions of applicable prefixes

‘The basic units and the derived and supplesencary unite which will
normally be required for road design are listed in Table 1.2.2.

TABLE 1.2.1 + DEFINITIONS OF PREFINES

PREFIX sumo FACTOR DY wiICu TUE UNIT
IS MULTIPLIED
mes $” 106
kite x 10°
necto a 10%
ees A 107
cents © 107?
sou . 10°
micro » 1076

]

5. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER à

GENERAL Page1.3

sams 1.2.2. à SIC UNITS, MUTIPLES ao SUIS
am = um ET
qee = pe AND SUB-MULTIPLES
engin | nee = [ae
imo won | m | mom
ei secos » | ay coro.
un
ea A | of | ra, nectaretanaetocooe
ia
Witter | eaten |!
fue
o | nes 5 ae
Y 10000 astetes?)
> Fe
ensity | xitoacan ser | et | 2 more? = 2 29/1 az
vs | soe » [mn ,
Tai ere gt 9.009
Pressure newton per wife? 0/00?
D | Shure ee
verocity | mue | we AOS
(speed) | second EX
mue | essen © | mime 63, second
= ‘sea circle)
grade $ (4007 circle)
ae || mm te

6. ROAD DESIGN MANUAL
ian IC DESIGN OF RURAI

L_ROADS

GEOMETAL

7. ROAD DESIGN MANUAL
& PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 1: GENERAL Page 1.5

HORIZONTAL CURVE

centre pont m centre pact M

SUPERELEVATION

ne | tangent to eine cette origino |] 7 | tongent length

face | egin ot cicie tom ciottoig ent ||P | Point of intestction (noizoto!?
eee | tra of circo te cto | cision angte (gonna)

tei | tenet ot once 5 | Rote of change of superetevtion
tee | swe: curve engin Ceirte sctthowe? || | contre = tine of rod

FIGURE 1.3.2 STANDARD SYMBOLS ANO ABBREVIATIONS FOR HORIZONTAL

CURVES ANO SUPERELEVATION

8. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 1: GENERAL Page 1.6

VERTICAL CURVE

sano DescRIPTION ETS DESCRIP
9 Tores 1m eve | Beginning of verticel curve

st | stetion cnaimage y | Tongent ottset (vertices)

m | Weight above see teves (m) | Horizontal tengin in plan

Re | cquivatent raaivs ot vericoscorvetm) | ¢ | centre correction

ase | Length of vertical curve im} is

80 | aigeroie aitterence in gradients 0%) | um

FIGURE 13.3 STANDARD SYMBOLS AND ABBREVIATIONS FOR VERTICAL CURVES.

9. & | PART 1: GEOMETRIC DESIGN OF RURAL ROADS

ROAD DESIGN MANUAL

CHAPTER 2 à THE ROAD SYSTEM Page 2-1

Roads have two basic traffic service functions which, from a design
standpoint, are incompatible. These functions aro:

(6) to provide traffic mobility between centres and areas; and

(41) to provide access to land and properties adjoining the roads.

For roads vhose major function 18 to provide mobility, 1.e. to cater
for through and lons-distance traffic, high and unifore speeds and
Uninterrupted traffic flows are desirable. For roads whose major
function 1s to provide land access, high speeds are unnecessary and,
for safety reasons, undesirable. Thus, the function of a particular
road in the national, regional and local road network has a signifi
cant impact on the design criteria to be chosen, and the design engineer
has to give careful consideration to this aspect in the early stages

Of the design process. ‘The following steps are required

1. Classification of the road in accordance with ite major

2. Determination of the level of access control compatible with
the function of the read.

3. Selection of geometric design standards compatible with
unction and level of access control.

Wen the functional classification and Level of access control are
given, design standards can be applied which will encourage the use
(Of the road as intended. Design features that can convey the Jevel
Sf functional classification to the driver include carriagevay width,
continuity of alignmcat, spacina of junctions, frequency of accesses,
standards of alignnent and grades, traffic controle and road reserve
wiatne.

10. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CUAPTER 2 : TUE BOND syomen da

OAD CLASSIFICATION

‘The ronds in Konya are divided Into the following 5 classes according
to their major function in the road networks

25 A= international Trunk Road

Roads Linking centres of international importance and crossing
Anternational bourdaries or terainating at international porte.

Clase - National Trunk Roads:
Ronde Linking nationally important centres. (Principal Towns/
Urban centres).

less € - Primary Ronde

Roads Linking provincially important centres to each other or to
higher class roads. (Urban/Rural centres)

Class D- Secondary Roads:

Roads Linking locally important centres to each other, to a sore
important centre, or to higher class roads. (Rural/market centres)

Class E

Minor Roads:
Any road Link to a minor centre Warket/tocal centres).

Roads of the highest Classes, A and B, have an their major function
to provide mobility, while the function of Class E roads is to provide
access, Tha roads of Classes C and D have, for all prectical purposes,
fo provide both mobility and access, with emphasis on nobility for
Primary Roads and on access for Secondary Roads. These roads are
‘generally the most difficult to design as far as traffic safety and
‘Operation are concerned.

‘This classification systen is basically a systen for rural roads as
far as function is concerned, although for adninistrative and financing
purposes it £a also carried through townships and municipslities
Within urban reas the rond network should, in addition, be function
ally classified according to the guidelines given in Part I ef this
Manual (Design of Roade in Urban Areas).

11. ROAD DESIGN MANUAL ]
PART1: GEOMETRIC DESIGN OF RURAL ROADS

Came 2 + me KAD Bren Ez

como or access

Uncontrolled access to roadside development along roads whose major
function is to provide mobility will result in an increased accident
hazard, reduced capacity and early obsolescence of the roads. In
order to preserve major roads as high standard traffic facilities it
is necessary to exercise access control, vhereby the right of owners
or occupants of land to access is controlled by the Highway Authority.

Although control of access is one of the most important means for
preserving the efficiency and road safety of major roads, roads with-
fut access control are equally essential as land service facilities.
‘The following three levels of access control are applicabl

(2) Full access control - means that the authority to control
access is exercised to give preference to through traffic by
providing access connections with selected public roads only
and by prohibiting direct private access connections

(2) Partial access control - means that the authority to control
access is exercised to give preference to through traffic to
a degree in that, in addition to access connections with
Selected public roads, there may be (some) private access.
connections.

(3) unrestricted access - means that preference is given to local
Traffic, with the road serving the adjoining areas through
direct access connections. However, the detailed location
and layout of the accesses should be subject to approval by
‘the Highway Authority in order to ensure adequate standards
of visibility, surfacing, drainage, etc.

Road function determines the level of access control needed (see
Séction 2.2). Motorways should always have full control of access.
For all-pirpose roads the following general guidelines are given for
the level of access control in relation to the functional road
classification:

LEVEL OF ACCESS CONTROL
ie Cu DESTRABLE REDUCED
a run Partial
» ra Partial
c Full or Partial | partial
> Parral Unrestricted
E Partial or Unrestricted
Unrestricted

12. ®

| ROAD DESIGN MANUAL
PART1: GEOMETRIC DESIGN OF RURAL ROADS

| — =

The reduced levels of access control my have to be applied for sone
road projects because of practical and financial constraints.

Control of access is accosplished either by the careful location of
accesses, by grouping accesses to reduce the number of separate con
nections to the through traffic lanes or by constructing service
Toads which intercept the individual accesses and Join the through
Janes at a Limited number of properly located and designed junctions,
In every cose the location and layout of all accesses, service roads
and Junctions should be carefully considered at the design stage and
Ancluded in the final design for the project.

13. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

‘CHAPTER 2 + THE ROAD SYSTEM Pago 2.5

ORD RESERVES

Road reserves are provided in order to accomodate future road con
nections or changes in alignment, road wideh or Junction Leyout for
existing roads and to enhance the nafety, operation and appearance
of the roads. The road reserve should always be determined and show
on the final design plans for road projecte.

The following road reserve vidths are applicable for the different road
classes:

ROAD RESERVE WIDTH (m)
PONCTIONAL CLASS
Desa REED

a so æ

» | so “©

e | 4 ©

» 25 25

B 2 20

‘The reduced widths should be adopted only when this is found necessary
for economic, Financial or environmental reasons in order to preserve
valuable land, resources or existing development or when provision of
the desirable width would incur unreasonably high Coste because of
physical constraints.

For dual carriageway roads it may be necessary to increase the road
reserve width above the given values, As a general rule the Toot
reserve boundary should be at a distance fron the centreline of the
nearest carriageway equal to half the road reserve vidth for single
carriageway roads.

14. & | PART 1: GEOMETRIC DESIGN OF RURAL ROADS

ROAD DESIGN MANUAL

CHAPTER 3 + DESIGN CONTROLS AND CRITERIA Page

sa

Es

‘The geometrie form of a road consists of a number of geomctric design
elements. Appropriate standarde and combinations of these elenente
Should be determined on the Basis of the following controle and
eriterss

= Environmental considerations.
= Rosa safety considerations. .
= Road function and control of access.

= Traffic volume and capacity.

= Design speed and other speed controls.

= Design vehicle and vehicle characteristic

= Economic and finaneie considerations.

The design engineer should consider all these controle and criteria,
in order to arrive at a final design which is in balance with the
Physical and social environment, which meets future traffic require
menta and which encourages consistency and uniformity of operation.
In this way it 13 possible to eliminate at the design stage any
environmental and Operational problems which would otherwise increase
accident potential and other detrisental effecte and incur costs for
Fenedial measures in the future

Alternative construction technologies incorporating Labour intensive
methods have a bearing on design criteria for lower class (D and E)
roads; these cases require special consideration and sometimes à
relaxation of the standards mentioned in this manual.

15. | ROAD DESIGN MANUAL
& PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 3 + DESIGN CONTROLS AND CRITERIA Page 3.2

3.2 ROPOGRAPHY, LAND USE AND PUYSICAL FEATURES

Road design is an exercise in three-dinensional planning whose success
Will be measured not only by the efficiency of the road but by ite
appearance and impact upon the adjoining ares.

A fundamental consideration in route location and final design is to fit
the road sympathetically into the landscape, vith a broad avarenens of
the character and features of the area through which it passes. This
4s required not only to obtain an aesthetically pleasing alignsent,

but in general is also necessary in order to obtain the most economic
solution and the best possible service to the traversed area with the
least detrimental effects.

Topography is a major factor in determining the physical location,
alignment, gradiente, sight distances, cross-section and other design.
elements of a rural road. In flat terrain the topography may have Little
Anfluence on location, but At may cause difficulties in some design
elements, e.g. drainage. Furthermore, it may encourage monotonous
straight alignnents with abrupt changes in direction which may be
surprising and difficult to recognise by drivers because the topo-
raphy gives no indication of what to expect.” In mountainous terrain
the route location and certain design features may be almost entirely
governed by the topography.

Geological, soll, climatic and drainage conditions also affect the
location and geonetrics of a road. Of particular importance is the
Prevention of soil erosion.

Man-made features such as agricultural, industrial, commercial, resid-
ential and recreational developments are inportant controls for the
route location and final design. Care should be taken to avoid
unnecessary destruction, denolition or severance of valuable properties.

Information regarding topography, land use and physical features are
essential and should be obtained in the early stages of planning and
design. In this respect it ie necessary to consult with the physical
Planning authorities (Physical Planning Departsent and the Provincial
Physical Planning Officere) in order to co-ordinate the project with
existing and proposed land uses and to protect the selected route
from conflicting developaent.

16. | ROAD DESIGN MANUAL

(CHAPTER 3 + DESIGN CONTROLS AND CRITERIA

& PART1: GEOMETRIC DESIGN OF RURAL ROADS

3.3 ENVIRONMENTAL consrDERATIONS

Wo road project is without both positive and negative effects on the
environment. The location and design of a road should aim at maxis
ining the favourable effects of the project, such as providing or
Fenoving undesirable traffic from environnentaliy vulnerable areas,
Mille at the sane tise minimising the adverse effecte of the project
hs much as possible.

‘The following factors, related to the road as a physical feature in
We environment, have to be considered in the location and design of
a road project

(2) The preservation of the natural beauty of the countryside

(2) Te preservation of areas and land use of particular value,
including:
= national parks and other rece
= Wille and bird sanctuarse
= forests and other important natural resources
= land of high agricultural value or potential:
= other land use of great economic or employment importance; and
= historic sites and other mancmado features of outstanding value.

tonal areas:

(3) The prevention ef soil erosión and sedimentation.

(4) The prevention of health hazards by ponding of water Leading to
the formation ot maps.

CE

avoidance or reduction of visual Intrusior

(6) The prevention of undesirable roadside development.

Other considerations are mainly related to the operation of the road
as a facility for moving traffic and include the following detrimental

= Noise poltution,
= Air pollution.

© Vibration.

= Severance of areas (barrier effect).

‘These operational effects are mainly a problem of urban roads and
traffic, but in some Cares are also relevant to the design of roads
in rurel areas.

Some of the adverse environmental effects are fairly easy to quantity
(e.g. noise levels and air quality), whilat others are more difficult
(e.g. visual impact}. In many cases it ie neceasery to seek the advice
and services of Other professions to reach à proper evaluation of the
Problent and establish adequate remedial measures.

SSS

17. PART 1: GEOMETRI

3 à DESIGN CONTROLS AND CRITERIA

ROAD SAFETY CONSIDERATIONS

pesigning safety into roads 1s one of the main objectives of Sentido
Designing e ey features applicable to a given type of road should Do
den ko the road during ite initial construction.

safety considerations in road design have two different objectives:
(4) Te provido design features aimed at preventing accidents, and

(4s) To provide design features aimed at reducing their sersousnese
when they occur

vor te prevention of accidents the following points ere of particular
importance:

(2) Provision of physical separation between motor vehicles and
Frost cea traffic (pedestrians, cyclists, animals) i and
to facilities for these two road user typen.

(2) Provision of a belanced design, 1.6. compatibility Between
the various design elements.

(2) avoieance of surprise elements for the drivers: 4-0; 00
changes in standard, adequate visibility conditions
a pmasing of horizontal and vertical alignment.

(4) avoidance of situations where drive
One decision at a time,

.a must make more than

(5) Provision of design features thet reduce speed differentials
Provision icles: 0.9. flat grades and speed change Lanes

(6) Proper location and design of junctions with perticeler
o on sufficient aight distances, a minima of confiar
ee clearly defined and controlled traffic movements

a) Proper design, application and location of traffic signs,
Parkings and other traffic control devices.

(81 Provision of design elements compatible with traffic volines
not traffic (long-distance, through, local, etc).

(&) Provision of proper drainage of the road surface.

because of the hunan element involved, sone accidents vill Nappes S218
Because of tne en high safety stondarde. Therefore, a basic constó”
on Toss serie design 15 to minimise injuries end Gamage when
gration i" arroccur. Important points in this respect aros

18. ROAD DESIGN MANUAL |

PART 1: GEOMETRIC DESIGN OF RURAL ROADS

E ee

e

©

w

(or

Roadside slopes should be ande as flat as feasible,
desirably 1:4 or flatter, and the roadside aren should be
ell rounded where slope Planes intersect.

Rond sign and Lighting supports and other utility poles
fahould be located far enough from the carriageway Lo make
then unlikely to be struck by an out-of-control vehicle, or
they should have breakaway capability.

ALL drainage structures should be designed so that out-of-
Control vehicles can either pass safely over then or be
safely detected,

Safety fences should be considered only when £111 slopes of
1:4 or flatter are not feasible, and the damage caused by
hitting the safety fence would be less serious than damage
Exon leaving the carriageway,

Safety fences should be provided at dangerous obstacl:
which cannot be renoved, and which would cause serious damage
Te hit by an out-of-control vehicle (6.9. bridge piers and
abuesents)

Road safety considerations and features are built into the principles,
criteria and values for the various design elements given in the hose
Design Manual. However, this does not necessarily ensure that the

completed rond will be of a safe design unless the design engineer is

fully avare

‘and takes into account, the road safety anpeete through

out al phases of the design work.

19. ROAD DESIGN MANUAL | u
®& PART 1: GEOMETRIC DESIGN OF RURAL ROADS
CCUAPTER 3 DESIGN CONTROLS AND CRITERIA Par
[ [ae |

25

BORD FUNCTION AND LEVEL OF ACCESS CONTROL

‘The function of a particular road, ar defined by the majority of the
road users (long-distance traffic, through traffic, local trafics
ete.) has to be taken into account in the determination of design
standards for the project and in particular in the selection of the
design speed (Section 3.7) and cross-section (Chapter).

In particular, careful consideration must be given to the choice of
design standards for ronde whose major function Le te cater for Longe
distance regional traffic (generally A and B Class roads). Because
of the long atstances involved, traffic tends to move at high speed‘
fn sone of these roads, and it may therefore be necessary to adept
higher standards than are warranted by traffic volumes In order to
Provide an acceptable level of road safety

Guidelines for the selection of design standards in relation to road
function are given in subsequent chapters for a nunber of design

Depending on the function ef a road, various levels of access control
Rhould be imposed as described in Section 2.3. All points of access
should be carefully considered and planned at the design stage. Access
should not be allowed at locst ions where entering and leaving vehicles
will create a hazard, particularly where sight distances are restricted
oF at points too close to other junctions. The proper location and
design of access points may in sone cases necessitate adjustments to
the initiol eligneent.

More comprehensive guidelines and standards for access control and
the location and layout of accesses and other rosdside features are
Given in the Manual on Roadside Developaent and Control =

FRE yer aia

20. ROAD DESIGN MANUAL
ATI: GEOMETRIC DESIGN OF RURAL ROADS

36

{TRAFFIC VOLUME AND CAPACITY

The design of a road should be based upon factual data on the traffic
volumes which the road will have to accomodate, The usual design
Control le the Design Voluse, which is the estimated traffic volume
fat a certain future year, the "Design Year", usually 10 years after
‘the year of opening of the new road.

‘Te general measures of vehicular traffic on a road are:

(2) Average Annual Daily Traffic (MOT) = the total traffic
volume for the year divided by 365.

(2) Average Daily Traffic (ADT) - the total traffic volume
Guring a given tine period in whole days greater than one
day and less than one year divided by the number of days in
that tine period.

‘me most adequate design control for low-volume roads is MADT in year
10 after opening, estimated fron historical AADT data and the envis-
aged socio-econoaieal development pattern. For routes with large seasonal
variations but still moderate traffic volumes, it may be sufficient to
determine the Design Volume in year 10 after Openingas AUT during the
peak months of the year.

On major roads carrying relatively heavy traffic volumes throughout
the year (current MAT > 1000), hourly traffic has to be used for
determination of the Design Volume. However, it would obviously be
Wasteful to design the road for the maximum peak hour traffic in the
design year, since this traffic volume would occur only during one

for a very feu hours of the year. As a general rule, heavily trafficked
rural ronde should be designed to accommodate the 36th to 50th highest.
hourly volume in year 10 after opening (DEV = Design Hourly Volume),
depending on economie considerstions.

When the Design Volume exceeds 8,000 pcu's a dual carriageway may be
Considered, particularly if the road traverses through a typical
rural area such as do the Mosbasa-Neirobs and Naivasha-Nakuru roads.
Close to major tome a single carriageway road may carry a Design
Volume of up to 15,000 peu's.

Although most new roads in Kenya will carry traffic volumes far
below capacity, the designer must be aware of the Basic and Design
Capacities of the new road.

‘me Basso Capacity of a road £e the maximum number of vehicles that
Can pass over a given section of a lane or carriageway, in one direc
tion (or in both directions for a two-lane highway), during a given
Period (ene hour unless otherwise specified) under prevailing xoadvay
ana traffic conditions. The traffic flow at this level is unstable and
minor disturbances in the traffic streams may cause stop-go operations

21. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CCUAPTER 3 ı DESIGN CONTROLS AND CRITERIA

Consequently the Design Capacity of a road is taken as less than the
basic Capacity, and if Unually related to à "Level of Service” which
expresses the effectiveness of the road in terms of operating condit-
fone. The choice of Level of Service shall generally be based on
economie considerations.

In Table 3.6.1. guide values for capacities aro given. These values
are based on data frou other countries and should be used only as a
rough guide to capacity until more reliable values for Kenya roads,
have been established.

FABLE 3.6.1. + BASIC AND DESIGN CAPACITIES FOR 2-LANE RURAL ROADS,
ixcloding the effects of reduced lane widthe and
lateral abstructions)

asic capacity | operating | Design | Proportion | estan
fore inne” | Speed Speed | of fond | capacity
Single carriage
wr signe aie.
| greater
leo Ga) usm) | Yan wem
sini
reqviresent
2000 95 | mono | 1008 400
ES 360
ES Es
2000 eS so-100 | 1008 100
| ES 700
oe >
| ES =
= Ts le 10 Jus
| ' EN 1060
| EN 30
| EN "eo
ES ES
2000 s |» lo 1200
ES 1200
EN tao
oo loro
| ES 800

‘me capacity values in Table 3.6.1 above are expressed in Passenger
Car Units in order to take into account the influence on capacity
Of different venicle mixes on different gradients,

22. ®

ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 3 : DESIGN CONTROLS AND CRITERIA

‘the following guide values are given for the conversion factors
applicable to different vehicle types in different types of terrain:

visio ms nav terroin | Pois |ourtatsooe
agar ours ones e EE
A | 10 » Lae * [ae =
pa | 25 = [so = Jo +
mer each [xs [es » [wo -
ee mo + |ao - [ce -
wei ns © jae © [as ©
Petal qe os ® fos = In

Riso representative for combined group of sediuz and heavy goods
vehicles and buses

‘the following definitions apply to the different vehicle types
Zentioned in the above tables

Passenger cers: Passenger vehicles with less than nino
Light goods vehicles: Land rovere, minibuses and goods vehicles
Of less than 1500 kg unladen weight with
payload capacities of less than 760 kg.
Mediun goods vehicles: Maximan gross vehicle weight 8500 kg.
Heavy goods vehicles: Gross vehicle weight greater than 8500 kg.

uses: ALL passenger vehicles larger than nini-

Example: An hourly traffic volume of 40 passenger cars, 20 Light
Goods Vehicles, 10 edits goods vehicles, 5 heavy goods vehicles and
"buses totalling 80 vehicles, in mountainous terrain represents 60 +
Go + 100 4 100 + 30 = 150 Passenger Car Units per hour.

on roads with two Or pore lanes in each direction, and on 2-lane
Single carriageway roads where important junctions are encountered
Gr there additions: lanes are to be provided later, knowledge of the
hourly traffic volune An each direction of travel Is fot for
design.

23. ROAD DESIGN MANUAL
& PART 1: GEOMETRIC DESIGN OF RURAL ROADS
CHAPTER 3 + DESIGN CONTROLS AND CRITERIA Page 3.10

For a more comprehensive treatment of capacity values and methods
for calculating capacity, reference 18 made to the Highway Capacity
Manual for Kenya

At As enphasised here that pavesent design requires a different vehicle
type classification to that used for deteraining peu factors which
refers to payload, tare weight or nunber of axlesı and further, à
different definition of "design year” may be used, eg. 3 years, 10
years or 15 years after opening of the new rosa

Draft oniy

24. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 3 + DESIGN CONTROLS AND CRITERIA PR

DESIGN SPEED AND OTHER SPEED CONTROLS

‘The Design Speed is a speed determined for the design and correlation
of the physical features of a road that influence vehicle operation.
Te de the maximun safe speed that can be maintained over a specified
ection of road ven conditions are 20 favourable that the design
Features of the rond govern.

Sone design elements, e.g. curvature, superelevation, sight distance
and gradient are directly related to, and vary appreciably with,
Gesign speed. Other features, like carriageway and shoulder widens
are less directly related to design speed, but because they can affect
vehicle speeds, higher standards for them ‘should be used on ronds vith
higher design speeds. Thus, nearly all the geometric design elements
of the road are affected by the selected design speed.

Economic and environmental considerations should determine the select-
Son of design speed, which is influenced by the following factors:

(a) The classification and function of the road

(D) The nature of the terrain.

(€) The density and character of the adjoining Land use.

(a) The traffic volumes expected to use the rond.

As these factors usually vary along a route of some length, the design
‘speed does not have to be constant for the whole length of a road. On
the contrary, changes in the design speed are usually required in order
to obtain proper correlation between the road layout and the above
factors, Whilst maintaining construction costs at realistic levels.

‘Guiding values for the selection of design speed are given in Table
3.7.1.” The following general guidelines should also be considered:

(4) Drivers on long-distance journeys” are apt to travel at higher
speeds than local traffic. This should be taken into account
when selecting design speed for major trunk roads.

44) On local roads whose major function ie to provide access, high
‘speeds are undesirable and the design speed should be selected
accordingly.

(111) Drivers do not usually adjust their speeds to the importance
of a road, but to the physical Limitations and prevailing
traffic conditions. Muere a aifficult location 18 obvious to
the driver, he is more apt to accept a lower speed of oper-
ation than where there is no apparent reason for it. A low
design speed should not be assumed for a road where the top
‘ography is such that drivers are apt to travel at high speeds.

25. &

ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 3 à DESIGN CONTROLS AND CRITERIA Page 3.12

(sv) Economic considerations (road user savings ve. construction
costs) zay justify a higher design speed for à road carrying
large volumes of traffic than for a less heavily trafficked
road in similar topography.

(e) changer in design speed, 41 required, should not be effected
abruptly, but over sufficient distances to enable drivers to
change speed gradually. The change in design speed should not
be greater than 254 and the section with the lower geometric
etandards should be long enough to be clearly recognineable
by drivers (not, for example, Just one single curve).

1t ie important to note that the design of a road in accordance with
a chosen design apura does not necessarily ensure a safe design. The
Various design elements have to be combined in a balances vay, avoiding
the application of minimum values for one or a feu of the elements at
a particular location vhen the other elemente are considerably above
the minimum requirements. As a general rule, speeds selected by the
yond users are determined more by the horizontal than by the vertical
alignment.

TABLE 2.7.1 + GUIDE VALUES POR SELECTION OF DESIGN SPEED (km/h)

‘TERRAIN OAD CLASSIFICATION
Level 100-120 | 90-160 so
| Rolling 70-100 | 60-90 50-80
| mountainous sor | 20-0 20-50

The following definitions apply to the different types of terrain
referred to in the above table:

Level Terrair

Level or gently rolling country which offere few
obstacles to the construction of à road having
continuously unrestricted horizontal and vertical.
alignment (transverse terrain sloge around 5%).

Rolling Terrains Rolling, hiliy or foot-hill country where the slopes
generally rise and fall soderacely gently and
here occasional steep slopes nay be encouncered.
Te vill offer sone restrictions in horizontal and
vertical alignnent (tranaverse terrain slope around
on.

26. ROAD DESIGN MANUAL |
{GEOMETRIC DESIGN OF RURAL ROADS

& ne
CHAPTER 3 + DESIGN CONTROLS AND CRITERIA | Page 3.33

Terrain Rugged, hilly and sountainous country and river

gorges. Tis clase of terrain imposes definite
restrictions on the standard of aliguaent ohtain-
able and often involves long steep grades and
Limited sight distances (transverse terrain slope
up to 700).

27. ROAD DESIGN MANUAL
& PART 1: GEOMETRIC DESIGN OF RURAL ROADS
(CHAPTER 3 + DESIGN CONTROLS AND CRITERIA Page 3.10

DESIGN vemcuss

‘The physical characteristics of vehicles and the proportions of the
various sizes of vehicles using the road systen are positive controls
In geonetric design. The principal vehicle dimensions affecting design
are the minimum turning radius, the path of the inner rear tyre, the
tread wider and the Wheelbase. Te principal design elements affected
are the cross-section of the road, rond widening in horizontal curves
and junction Layout. Until detailed information on the aifferent
vehicle types using the roade in Kenya becomes available, the follow
ing three design vehicles should be used as controle in Jeometric
design

Design venscte | mesibase | Front | near | over | over- | uesont|
over |over- | tl | ail
hang | hang | Tengen | vias

Passenger car | 2.48 | 0.92 [12 | 5.0m [1.08 | -

Single unit
truck (ie
overatl) 658 | 1.58 [3.08 [1.02 [25m | 3.0%

Semi trier
combination [4,048.48
Ga overaiı) [13.92 | 1.28 [o.6m [iso |2.5m | 2.08

Dimensions and turning radii for these design vehicles are presented
fon pages 3.18, 3.15 and 3,16 An 1:200 scale diagrans.

28. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 3 - DESIGN CONTROLS AND CRITERIA a

18

ovennano,
‘OUTER FRONT WHEEL

DIMENSIONS AND TURNING RADIUS FOR A PASSENGER CAR

29. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

Page 3.16

CHAPTER 3 - DESIGN CONTROLS AND CRITERIA

OVER
ure Font

INNER REAR WHEEL I m \ a ; !

a

DIMENSIONS AND TURNING RADIUS FOR A SINGLE UNIT TRUCK (Mim OVERALL)
SCALE 1200

30. ROAD DESIGN MANUAL
& PART 1: GEOMETRIC DESIGN OF RURAL ROADS
à CHAPTER 3- DESIGN CONTROLS AND CRITERIA PE

DIMENSIONS AND TURNING RADIUS FOR A SEMI- TRAILER COMBINATION

(15m OVERALL) ALSO APPLICABLE FOR TRUCK (TANKER) PLUS TRAILER

31. ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

(CHAPTER 3 + DESIGN CONTROLS AND CRITERIA Page 3.10

2.9

ECONOMIC CONSIDERATIONS

‘me relationship between costs and benefits 18 a measure of Justif-
Seation, and often a deciding factor in determining the geometric
features of design. The costs include right-of-way (road reserve),
construction, maintenance and vehicle operation. The general value
resulting from an improved road Link includes services and benefits
to the country, community and road users. A high geometric design
Standard is varranced vhere there are sufficient benefits to road
users to justify the additional coste above that of a low design
standard. Particularly in the stages of planning the preliminary
design when decisions regarding location and general design parameters
are sade, the relationship between costs and benefite for different
alternatives is of great importance.

Preliminary or approxisate cost estisates should be made for each
Alternative plan. All major items should be included; road reserve
acquisition, site clearance, earthworks, drainage, fe, abructures
and, Where significant, relocation of utility services and the cost of
maintaining traffic during construction. Estimated annual costs of
maintaíning and operating the roadways, roadsides (@itches)and struc~
fares should also be included if there appear to be significant
differences between alternatives.

To complete a monetary analysis of alternative plans, the total road
user coste should be determined for each alternative, Road user coste
are the drivers’ vehicular operating costs and, where relevant, the
value of (gained) time. The total of the road user costs for each
alternative plan can be a good factor for comparison as they reflect
speed, distance (directness) and operating conditions.

À computer model called the “Road Transport Investment Model” (or
the “Highway Cost Model"), which estimates the costs of different
investment strategies for rural roads in developing countries, is
Operational in Kenya. It is based on research carried out mainly in
Kenya by the British Transport and Road Research Laboratory, and it can
provide useful assistance to the design engineer, as long as up-to-date
and relíable input data, especially on maintenance (procedures and
Productivity) and vehicle operation, are readily available.

+ Bau THRE Reporte 672, 673 and O74, Overseas Unit,
Transport and Road Research Laboratory Crowthorne,

Berkshire, England.

32. | ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

| conven à Tu car

man

The major geometrác design elements constituting the cross-section
axe the çasriagewsy, the shoulders and the ditches and, for dual
Corriageway roads, the central reserve. The carriageway includes

the travelled way, any auxiliary lanes such as acceleration and
Geceleration lanes, clisbing lanes, passing and bus bays and ley-bys .

Also related to the cross-section are cycle tracks and footpaths.
Many roads in Kenya, particularly those providing access as their
major function, carry a considerable rusher of pedestrians and cyclists
who make use of the shoulders and carriageway cajes because separate
facilities for thes are not provided. From a traffic safety point of
View this 48 an undesirable situation and cycle tracks and/or footpaths
‘should be included in the cross-section where appropriate (at the cost
Of the width of the shoulders).

‘me selection of standards for the cross-section is dependent on the
Controls and criteria described in Chapter 3. Lane and shoulder widths,
(ditch) slopes etc. should be adjusted to traffic requirements (traffic
volume, traffic composition, vehicle speeds) and characteristics of

the terrain. This means that the cross-section may vary over a part-
Acular route because the controlling factors are varying. The basic
requirements are, however, that changes in cross-section standards
‘Shall not be made unnecessarily, that the cross-section standards shall
be uniform within each sub-section of the route and that any changes

Of the eross-section shall be effected gradually and logically over

E transition length. Abrupt or isolated changes in cross-section
Standards lead to increased hazards and reduced traffic capacity and
complícate construction operations.

in certain cases, however, £t may be necessary to accept isolated
reductions in cross-section standards, for example when an existing
harrow structure has to be retained because it ls not economically
Tensibie to replace it. In such cases a proper application of traffic
Signs and road sarkings 4s required to warn sotorists of the discon-
Einuity in the road.

in specific cases it may be economic to select a stage-construction,
Stes to construct a road to a gravel Standard in a first stage and
Anprove the road to a Bitumen standard when warranted by increased
traffic. The conversion from Gravel to bitunen has to be taken inte
account in the cross-section.

An order to simplify the selection and design of the cross-section
elements and promote uniforeity in standards, a set of standard cross

“tions has been laid down, and guidelines are presented for the
selection of the appropriate cross-section.

33. & PART 1: GEOMETRIC DESIGN OF RURAL ROADS

ROAD DESIGN MANUAL

CHAPTER 4 + THE CROSS-SECTION

Page 3.2

Type 1 Te Standard cross-section applicable to rural dual
carriageway ronde is shown in Figure 4.2.1

. u j
A, us

a
of > Ta coger de
NT Bay as yt ae un Ts yas yas

FIGURE 4.2.1 CROSS-SECTION TYPE 1 DUAL CARRIAGE WAY

Notes on Figure 4.2.1

(2) Tho slope of Hts lt whore AE € im
102 here In = ME € je
111.5 where ne >
(2) Type of Akten: 00 Section 4.4

13) The shoulder way be reduced to 1,500 in hilly and sountatnous

terrain. Widen the shoulder by 0.50 where guardrail 16
required.

(4) The central reserve should be widened where this can be done
may be decreased to 3.5m with a twin flexible guardrail in the
Centre. Central reserve planting should be of the hedge typey
and should protect against headlight glare from vehicles driving
‘on the opposite carriageway. Independent design of the two
Carriageways should be applied where this proves economica! .

34. ROAD DESIGN MANUAL

& PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 4 + THE CROSS-SECTION Page

Types T1-Vi21 The standard cross-sections applicable to rural single
Carriagewsy roads are show. in Figure 4.2.2 and
able 4.2.1

FIGURE 4.2.2 CROSS- SECTION TYPES 1 - VIH - SINGLE CARRIAGEWAY

notes on Figure 4.2.

(2) The slope of #411 whore one € im

14
2:2 where im Ch Ein

1.5 were ee
(2) type of Aire see Section 4.4

(2) Micen the shoulder by 0.50 where guardrail is required.

ALE 4.2.1 + STANDARD CROSS-SECTIONS FOR SINGLE CARRIAGEWAY RURAL ROADS

= ann mann lens aus
ons-scction 7;
T A ay

apo [ume | surem | a | >®Te 5
moe onu io [aso [roo | 25
u | 2 | on | #50 [2.00 [es | 25
w | 2 | men | 7.00 | 0.50 [6.00 | 25

v [ag | onen | mo Ins | sco | 25
vi 10 bitumen 5.00 | 0.50 | 4.00 2.5
va | 20 | graver eo | - - 40
vn | à Jevvenve | exo | - | - 50

Por notes See next page

35. ROAD DESIGN MANUAL ]
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

‘CHAPTER 4 à ‘THE CROSS-SECTION

Page 4.4

Notes on Table 4.2.1:

(a) wider

by 0.5m where guardrail required.

(2) Wide shoulders required to accomodate later uparading to Type IV.

(3) 8.0% width required to accommodate later upgrading to Type IV oF Y.

Single lane road to be provided with 6e vide paved meeting bays
every 300 to 500 depending upon intervisibility, and Gn vide

and 250m long paved overtaking sections every 5 to 10kn depending
Upon average travelling speed:

36. ROAD DESIGN MANUAL |
& PART1: GEOMETRIC DESIGN OF RURAL ROADS

te m pores lasse

‘THE CHOICE or cos

The choice of the cross-section elements depende on a nunber of factors,
the most important of which ore:

1, The traffic volunen which the road will have to accomodate.

We selected design speed.

3. ‘The road function, 1.0. the predominant type of traffic that the
road serves, for example, Long-distance” versus "access", or
heavy goods” versus “passenger cars”

TABLE 4.2.2 + RECOMMENDED CROSS-SECTION TYPES FOR TWO-LANE RURAL ROADE

amor or De in year 10 peu) | crose-tection nme
mor iso Ly, vu vir or var a
2502 mar <500 vom @
300 pair = 2000 man a

or 2 a
250< oH 500

Map = 4000
uv > 500

Notes on Table 4.2.2

(1) Selection of cross-section depends upon the classification of
the road

(2) types Y and VII are only interim solutions (stage construction).

(3) For A and 5 Class roads with design speeds greater than 90 km/h
the higher standard of cross-section should be chosen

For the selected cross-section, the most appropriate types of side
Gitches and cut-off ditches are to be chosen in accordance with the
guidelines given An Section 4.2.

37. ROAD DESIGN MANUAL

& PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CUAUTLA 4 à THE CROSS-SECTION Page 4.6

9 snclude bus bays,

Etesents complementary to the normal cross-sect
parking bays, eyele tracks and footpaths.

cyste tracks and footpaths, usually as a combined facility, shall be
Hess where the expected nunber of cycliste and pedestrians consid=
trably exceeds the nunber of motor vehicles, and reaches a level of
about 1000/aiy (cycles plus pedestrians). wherever possible the
Cycle trock/footpath should be separated from the rond. In flat and
felling terrain this can usually be achieved easily. However in hilly
nd sountainous terrain the cyele/footpath may have to be designed as
A eldening ot the shoulder.

pavenent widening required in horizontal curves is covered in Sects

5%. Climbing lanes are dealt with in Section 5.5. The design of

Speed change (Geceleration and acceleration) Lance ir included in
Gand 7 under "At grade and "Grade separated” Junctions

Nustays ant parking bays are provided in order to prevent vehicles
frog stopping and standing on the carriageway. The siting of busbays
(nich will also be used By matatus) and parking bays will depend
greatly po ‘The long established habits of

Public service and other vehicie drivers and their passengers shall
het be disregarded. Dus and parking Days shal] not be sited Where
Hs 12 resecictea." Typical layouts for these fasilisien are

som yanıanıe ven
Gm minimum)

FIGURE 4.2.2 SIMPLE BUS BAY (length dependent on number of buses
ard mátetas] Ukely to use the bay at the same time)

= om in YARN Gt, in 1

fom mi

FIGURE 4.2.3 HEAVILY USED BUS [ANO MATATU] BAY (Length dependent on
e EAU LEE 1 vee the Boy st he

Same time)

Pee aaa ee

FIGURE 4.3.4 PARKING BAY (length dependent on numbs
trucks (7N)ikely to park at the some time)

of cars (Nor

38. & | PART 1: GEOMETRIC DESIGN OF RURAL ROADS

ROAD DESIGN MANUAL

CHAPTER 4 + THE CROSS-SECTION Bas.

SIDE DITCHES AND cuz-orr pLTCHES

Generel

‘the types of side ditches and cut-off ditches which will generally
be used are shown on Figure 4.4.1 whilst Table 4.4.1 gives guidelines
regarding the choice of each particular type:

me guidelines given in Table 4.4.1 are based upon general econonic
Ind eestheete considerations, However, the type of side ditch selected
must be checked to ensure that it will carry the expected flow with
Cut running so deep ae to wet the road pavesent nor so fast as to

Due to their location, cut-off ditches are usually difficult to
maintain and should therefore, Whenever possible, be constructed
te "natural permanent depressions” with as gentle side slopes as
possible

Expectes Flow in sige pitenes

The side ditches must be designed to carry the stormater run-off
Griginoting fron the carriageway, shoulder, drain and cut slope
here cutoff ditches are not provided, any run-off from beyond the
Cot slope must also be included.

me expected flow, or run-off, should be estimated using the formula
gr 0.278 CLA

een pics ect ES
LO es oe o Be

ty of Side pitches

The capacity of à side aiteh should be estimated vsiny the mn
Berar eee gore

en
or Vanes CUT

ah coa

{5 Gh Srdegcevettonnt ares of water tw

were 0
Vis the velocity of flow (0/0)

iS the Roughness Coof ficient
35 the hydraciie radivs, A/F whore P is the

wetted perimeter
s Ie the longitudinal slope (2/0)

39. ROAD DESIGN MANUAL

& PART 1: GEOMETRIC DESIGN OF RURAL ROADS

CHAPTER 4: THE CROSS ~SECTION foe

TPE A =
“Cremation te

To.40 Min

TYPE a2

TPE Ba

mee 82

Tee 83

cut-off diten Type 10)

Cut off giten Type

Weight of cat | Slope (ray of cating ía | Distance,d Between, edge of
he | earth ot Cutting dna cut otf ditch
he < 100 1:3 e
100 <he «3.00 1.2 4
he > 3.00 nina A

(1) In rock the slope 1:n will vary trom 1:0-33 to 1: 0 10
(2) 11 earth not stable ot 1: 15, the slope maybe decreased to 1.2

if natural slope steeper than 1:13, then the natural slope may De used as the cut slope,
(2) The slopes into the ditch should be as indicated or flatter

FIGURE 43.1 SIDE DITCHES AND CUT - OFF DITCHES

40. ROAD DESIGN MANUAL
& PART 1: GEOMEIRIC DESIGN OF RURAL ROADS

CHAPTER € + THE CROSS-SECTION Page 4.9
Ls

ABLE 4.4.1 + GUIDELINES POR THE SELECTION OF SIDE DITON AND CUT-OPP DITCH TYPES

Er
BUS] ue Ow following =.
me mon
A | witty co souneatnous verraim vich | sack stope to be warten
= tr ir according to stabiiity of
for nectar. Slope ttowia
Sei atabte and enable vet“
“tune aaa
{2 | Rotting vorreim vith core coran] sa for ar
LD to mountainous terrain were
| Matter atten shen an ig requires
due to capacity and/or voley
tinstectones
i DE Sl
2 | ttiny to soutainous terrain where Take dor ay
| flattervaleen than Au ie required” | mach may be increased dt
| Gee co capacity and/or velocity | Til enr gere Lt
E

Rolling terrain with moderate “Ae for Bi

earthwork where a {latter ditch

than AZ is required due to cape
ty and/or velocity Tiettacion

Her

83 À Plat terrain with little corumork.

| Rolling terrain with moderate !

earthwork where à flatter ditch

than 82 Le required te capacity

and/or velocity limitetione

—

— 4
Giter | 70 be una under the following mis i
: fendi tions
X [moderate catctsont area and tie
chance of siltation
|
2 | sarge catchment ares and in areas | |

Hable to silting and/or danage t
to the ditch profile by pedest:

41. &

ROAD DESIGN MANUAL |
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

‘CHAPTER 4 : TRE CROSS-SECTION pipi do

Linstin values for the velocity of flow () to prevent ecour,
Yogether with the corresponding Roughness Coeficiente, are given in
Table 4.6.2 for the different types of ditch material which will

TABLE 4.4.2 + MAXIMO PERWISSIBLE VOLOCITIES IN ERODTBLE DITCHES
‘BRD CORRESPONDING ROUGENESS COEFFICIENTS

see opacas
Sand, loam, fine gravels

voleante ash. os as
suits clay feu so
course gravel 15 40
Conglomerate, hard shale,

soft rook 2.0 25
Hard rock 10 25
Masonry 3.0

conerere 3.0 co

+ In areas where good grass cover is guaranteed, these values may
be increased up to a maximun of 1.5 m/s: in such cases à Roughness
Coefficient of 30 should be used. Where grass cover is expected
but not guaranteed a maximum velocity of 1.1 m/s should be used
With a Roughness Coefficient of 30.

To facititate the rapid caleulation of side ditch capacities, Figures
4.4.2 - 4.4.6 are given. These figures show, for each side ditch type,

city varies for different ditch gradients, Roughnes
Coefficients, velocities and depths of flow.

It Se important to note that a side ditch will only perform as designe?
Lf the design eroms-sectäon ia maintained, Lie. excessive scour must
be prevented, In practice, due to local inconsistencies tn roughness
and surface level, no sige drain in any but the hardest of materials
Will be inzune {roe scour, Thus, for long lengths of side ditch at
Gradiente in excess of 8-58, scour checks should be considered.

Scour checks should be designed as control sections and will thus
match the side ditch erose-euction so as not to cause an obstruction
Much vould raise the water level, Careful consideration must be given
Yo the spacing of scour checks; much spacing Will net be constant but
Should reduce as the flow increases

42. Page 6.11

8

Es

2,
PE
FRE
22
Lul '
Zu

al 2
83°
Ga ul :
Bye] Ff
Gel 5
oi «| À
ZE À *
CFE 4
do à

E

É

a

ALiovayo

vewocity y

or

CAPACIT

43. 3
a

CHAPTER &

ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS

——

6%

$ ovev

ozo

ovo
800
100
so
soo

00

coo

200

0100

800 0
-400°0
9000
5000

00:0

00:0

vetocity y

IDE DITCH TYPE A.2

3 capacity or

FIGURE 4

44. ROAD DESIGN MANUAL

& PART 1: GEOMETRIC DESIGN OF RURAL ROADS
|
|
|
olx
E on
É 0.008

8 388888 E 3888888 2

MELON C0 ay =
+

45. Page 4.14

THE CROSS - SECTION

ROAD DESIGN MANUAL
PART 1: GEOMETRIC DESIGN OF RURAL ROADS
CHAPTER &

HE]

Ba

ses
$

&

vevocity

CAPACITY OF SIDE DITCH TYPE 8.2

FIGURE 44

46. a

PART1: GEOMETRIC DESIGN OF RURAL ROADS

ROAD DESIGN MANUAL

CHAPTER 4 : THE CROSS - SECTION

Page 4.15

capacity g

0.10

008
007
0.08
0.05

0.0%

00

0.02

0.001

veLocity y
x

FIGURE 4.4.6 CAPACITY OF SIDE DITCH TYPE 8.3

47. ROAD DESIGN MANUAL

& PART 1: GEOMETRIC DESIGN OF RURAL ROADS
li CUAPTER 4 + THE CROSS-SECTION

‘the side diteh type should mstch the adjacent terrain, e.
Gitches with gentle side slopes in flat open country and narrow
Gitches with steeper side slopes in

TE this principle 1s followed an economic and aesthet
generally be achieved.

48. | ROAD DESIGN MANUAL
& PART 1: GEOMETRIC DESIGN OF RURAL ROADS

De mo)

4.5 coscrau

Undivided pavenente with two or more lanes on tangents or Flat curves
Shall have a high point, or crown, along the centzeline with uniform
dommward slopes towards ach edge in order to facilitate surface
Mater run-off and to prevent mus from the verge fron spreading over
the carriageway. This downward slope ir terned cross fal

For rural roads with Lsturiocus pavenente the minimum crossfall shall
ke 2.50 and for rural ronde with gravel pavements Aux Lory
Yanes chell have a crosstal) of the sane direction and rate as the
adjacent lane. The crosefall on gravel or grass shoulders shall in
ALL cones be 4.08.

in curves, the carriajewsy will be supervievated in order to counter
balance part ef the centrifugal acceleration. The relationships
between Design speed, curvature and superelevation are described in
Section 5.3.4.