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UNIVERSITY OF NAIROBI

GEOMETRIC DESIGN OF CHANGAMWE – KWA JOMVU (A109A)

By Muthee Eric Mbugua, F16/36317/2010

A project submitted as the partial fulfilment for the requirement for the award of the degree of

BACHELOR OF SCIENCE IN CIVIL ENGINEERING

2015

DedicationTo my parents: Eng. Philip M. Muthee and Teresia N. Muthee who took me to school. There is no

doubt in my mind that without their continued support and counsel I could not have completed this

project. They have also helped me build my spiritual, personal and interpersonal skills.

Changamwe-Kwa Jomvu (A109A) ii May 2023

Acknowledgement The successful completion of this project would not have been possible without the effort of several

people who lent a helping hand and offered invaluable advice and insight. My sincerest appreciations to

all those who helped me make this report a reality.

I would like to acknowledge the help and encouragement of my father and mentor Eng. Philip M. Muthee

a registered Civil Engineer who has seen me through my studies not forgetting my mother Teresia a

Nurse who really did a good job in keeping me healthy and energetic as I sought further understanding

and solutions on Engineering problems.

I would like to acknowledge the inspirational instructions and guidance of Eng. Matheri my project

supervisor who has given me a deep appreciation and love for the beauty and detail of this subject.

Lastly I acknowledge my co-students who have contributed ideas, feedback and advice.

Changamwe-Kwa Jomvu (A109A) iii May 2023

Abstract

This study on geometric design of Changamwe – Kwa Jomvu Road was for optimum efficiency in traffic

operation and maximum safety at reasonable cost where Highway alignment, road classification and

Pavement surface characteristics were analysed.

A measure of the goods being carried from the port, shopping trips, the persons travelling to the airport,

the persons making marketing trips and those making work trips and how effectively these trips are made

was done. The measurement of these land- use involve determining the vehicle using the road daily by

type and freight they carry and purpose for which these trips are made. This is done by carrying out

classified traffic manual counts to determine the amount of traffic on the road, vehicle and vehicle loading

characteristics together with their origin and destinations. Thus such movements cover motorized and

non-motorized traffic. Consequently these data are averaged over the period of count, projected to the

design year for purposes of determining cumulative standard axles for pavement design and road capacity

assessment to reduce congestion.

Changamwe-Kwa Jomvu (A109A) iv May 2023

Table of ContentsLIST OF TABLES…………………………….…………………………………………….….….…....viii

LIST OF FIGURES ……………………………….………………………………………..…..…..x

LIST OF ABBREVIATIONS…………………...…..…….…………………….……..………...……....xi

Dedication………………………………………….…………………………………...………………… ii

Acknowledgements…...……………………….…...……………………………………………………. iii

Abstract…………………………………………....…………………………………………….……….. iv

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

1.1 General Overview of the subject..................................................................................................1

1.2 Background....................................................................................................................................1

1.3 Management of the Road Networks in Kenya............................................................................2

1.4 The Study Area..............................................................................................................................2

1.5 Problem Statement........................................................................................................................4

1.6 Objectives and Scope of the Study...............................................................................................5

1.7 Limitations.....................................................................................................................................5

1.8 Study Methodology.......................................................................................................................5

2. LITERATURE REVIEW....................................................................................................................7

2.1 The Road System...........................................................................................................................7

2.1.1 Road Classification................................................................................................................7

2.1.2 Control of Access.................................................................................................................10

2.1.3 Road Reserve (Right-of-way)..............................................................................................12

2.1.4 Topography, and Physical features....................................................................................14

2.1.5 Environmental Considerations...........................................................................................14

2.1.6 Traffic Generation Demand and Forecasting...................................................................15

2.1.7 Road Capacity......................................................................................................................15

2.1.8 Level of Service....................................................................................................................19

2.1.9 Design speed.........................................................................................................................20

2.1.10 Design Vehicles.....................................................................................................................22

2.2 Sight Distance..............................................................................................................................27

2.2.1 Stopping sight distance........................................................................................................27

2.2.2 Passing Sight Distance.........................................................................................................28

2.3 Pedestrian Facilities....................................................................................................................28

2.3.1 Footpath................................................................................................................................28

2.3.2 Cycle tracks..........................................................................................................................29

Changamwe-Kwa Jomvu (A109A) v May 2023

2.3.3 Pedestrian And Cyclist Overpasses And Underpasses (Subways)..................................29

2.3.4 Bus Bays................................................................................................................................30

2.4 Geometric Design Element.........................................................................................................31

2.4.1 General..................................................................................................................................31

2.4.2 The Cross- Section...............................................................................................................31

2.4.3 Shoulders and Ditches.........................................................................................................32

2.4.4 Medians.................................................................................................................................33

2.4.5 Headroom and Clearances..................................................................................................33

2.4.6 Horizontal Alignment..........................................................................................................34

2.4.7 Vertical Alignment...............................................................................................................37

2.5 Road Furniture............................................................................................................................42

2.5.1 General..................................................................................................................................42

2.5.2 Traffic Islands......................................................................................................................43

2.5.3 Kerbs.....................................................................................................................................43

2.5.4 Marker Posts........................................................................................................................43

2.5.5 Safety Fences........................................................................................................................44

2.5.6 Traffic Signs And Road Markings.....................................................................................44

2.6 The Project Area.........................................................................................................................45

2.6.1 General..................................................................................................................................45

2.6.2 Topography..........................................................................................................................45

2.6.3 Climate and Rainfall............................................................................................................46

2.6.4 Geology and Soils.................................................................................................................46

3. DATA COLLECTION.......................................................................................................................47

3.1 Introduction.................................................................................................................................47

3.2 DATA COLLECTION METHODOLOGY.............................................................................47

3.2.1 Preliminaries........................................................................................................................47

3.2.2 Topographical Survey.........................................................................................................48

3.2.3 Climate and Rainfall Data..................................................................................................48

3.2.4 Soil Characteristics..............................................................................................................49

3.2.5 Land use................................................................................................................................50

3.2.6 Inventory of the Road and Condition Survey...................................................................50

3.2.7 Historical Traffic Data........................................................................................................52

4. TRAFFIC STUDIES..........................................................................................................................57

4.1 Classified Manual Counts...........................................................................................................57

4.2 Diurnal Variations (Motorized Traffic)....................................................................................57

Changamwe-Kwa Jomvu (A109A) vi May 2023

4.3 Seasonality...................................................................................................................................58

4.4 Non–Motorized Traffic (NMT)..................................................................................................64

4.5 Origin – Destination (O/D) Studies............................................................................................65

4.5.1 Introduction..........................................................................................................................65

4.5.2 Traffic Zones........................................................................................................................66

4.5.3 Trip Matrices........................................................................................................................67

4.5.4 Trip Purpose.........................................................................................................................71

4.6 Traffic Forecast...........................................................................................................................73

4.6.1 Generated Traffic................................................................................................................73

4.6.2 Normal Growth....................................................................................................................74

5. DESIGN CALCULATIONS..............................................................................................................76

5.1 The straight..................................................................................................................................76

5.2 Vertical Alignment Design.........................................................................................................80

5.3 The Road Reserve.......................................................................................................................80

5.4 Drainage.......................................................................................................................................81

5.4.1 Sizing of Culverts and Side Ditches.......................................................................................82

6. RECOMMENDED DESIGN PARAMETERS................................................................................83

6.1 Geometric design.........................................................................................................................83

6.1.1 Cross-Section........................................................................................................................83

6.1.2 Horizontal Alignment..........................................................................................................83

6.1.3 Vertical Alignment...............................................................................................................83

6.2 NMT Facilities.............................................................................................................................83

6.3 Bus Bays.......................................................................................................................................84

6.4 Detailed Structural Design.........................................................................................................84

6.4.1 Sizing of Drainage Structures.............................................................................................84

6.4.2 Bridges..................................................................................................................................85

7. CONCLUSION AND RECOMMENDATIONS.............................................................................87

7.1 Installation of Bollards...............................................................................................................87

7.2 Introduction of speed humps......................................................................................................87

7.3 Traffic Signs and Road Marking...............................................................................................87

7.4 Street Lighting.............................................................................................................................88

REFERENCES...........................................................................................................................................89

APPENDICES……………………………………………………………………………………...…….90

Changamwe-Kwa Jomvu (A109A) vii May 2023

LIST OF TABLES

Table 2.1 Current Road Classification......................................................................................................9

Table 2.2 Summary of Current Road Classification in Km....................................................................9

Table 2.3: Level of rural access control...................................................................................................11

Table 2.4: Level of urban access control..................................................................................................11

Table 2.5: Rural road reserve width........................................................................................................13

Table 2.6: Urban road reserve width.......................................................................................................14

Table 2.7: Practical capacities of two-way rural roads..........................................................................16

Table 2.8: Practical capacities of two-way urban roads.........................................................................17

Table 2.9: Practical capacities of one-way urban roads.........................................................................18

Table 2.10: Recommended Design Speed (Rural)...................................................................................21

Table 2.11: Recommended Design Speed (Urban).................................................................................21

Table 2.12: Dimension of Design Vehicle.................................................................................................23

Table 2.13: Minimum Radii and side friction coefficient for horizontal Curves: 6% Super elevation

(Rural roads)..............................................................................................................................................35


(Urban Streets)...........................................................................................................................................35

Table 2.15: Desirable Maximum Gradients............................................................................................38

Table 2.16: Absolute Maximum Gradients.............................................................................................38

Table 3.1: Points of Study Locations........................................................................................................47

Table 3.2 for 12 month averages for the period under consideration...................................................49

Table 3.3 Soil permeability classification................................................................................................50

Table 3.4......................................................................................................................................................51

Table 3.5: Traffic Census point on the Trunk Road..............................................................................52

Table 3.6 Historical Traffic Data Table 3.7.2 (a) A14/6.........................................................................52

Table 3.7 (b) A14/23...................................................................................................................................53

Table 3.8 (c) A109/21.................................................................................................................................53

Table 3.9 (d) A109/26.................................................................................................................................54

Table 3.10 (e) B8/11...................................................................................................................................54

Table 3.11 (f) B8/13....................................................................................................................................55

Table 3.12 Average Growth in Percentage by Vehicle Class.................................................................55

Table 4.1: AWDT Factors per Day per Vehicle Type............................................................................57

Table 4.2: Seasonal Adjustment factor....................................................................................................58

Changamwe-Kwa Jomvu (A109A) viii May 2023

Table 4.3: Vehicle Composition per Segment by Proportion................................................................64

Table 4.4: Summary of Survey Results....................................................................................................64

Table 4.5: Two – Day O/D Sample as per vehicle classification............................................................66

Table 4.6: Conversion Factors for O/D Sample to AADT.....................................................................67

Table 4.7: A Summary of AADT O/D survey Data................................................................................69

Table 4.8: O/D Survey Occupancy Rating at Miritini............................................................................70

Table 4.9: Global Trip Purpose................................................................................................................71

Table 4.10: A Summary of Adopted Growth Factors for Traffic Forecasting....................................75

Table 5.1: Different design speeds and their maximum lengths............................................................76

Table 5.2: Passenger car units..................................................................................................................77

TABLE 5.3: EXAMPLE SERVICE VOLUMES FOR MULTILANE HIGHWAYS.........................78

TABLE 5.4 ACCESS CULVERT LOCATIONS....................................................................................79

Table 5.5: Geometric Cross section Types by pcu..................................................................................79

Table 5.4: Vertical Alignment Standards................................................................................................80

Table 6.10: Proposed structures...............................................................................................................85

Changamwe-Kwa Jomvu (A109A) ix May 2023

LIST OF FIGURES

Figure 1.1 Changamwe-Magongo site location map.................................................................................3

Figure 1.2 The study area in detail.............................................................................................................4

Figure 2.1. Speed vs Accessibility...............................................................................................................7

Figure 2.2. Road Reserve..........................................................................................................................13

Figure 2.3: Linkage between level of service (LOS), speed and flow/capacity.....................................19

Figure 2.4: Dimensions and Turning Radius for a Single Unit Truck..................................................24

Figure 2.5: Dimensions and Turning Radius Path for Single Unit Bus................................................25

Figure 2.6: Dimensions and Turning Radius for a Semi-Trailer Combination (15m overall) also

Applicable for Truck (Tandem) Plus Trailer..........................................................................................26

Figure 2.7: Typical illustration of cyclist envelopes................................................................................30

Figure 2.8: Simple Bus Bay Mainly for Use in Rural Areas..................................................................30

Figure 2.9: Bus Bay for Use in Urban Areas (Busy)...............................................................................31

Figure 2.10: Clothoid elements.................................................................................................................36

Figure 2.11: Vertical curves typical geometry........................................................................................41

Figure 4.1: Seasonal variation factor (From week 1 – 52).....................................................................59

PLATE 1 to 4: The Transport Mess at Kwa Jomvu Junction...............................................................65

PLATE 5 and 6: Passenger Carrying Vehicles Being Interviewed.......................................................66

Fig 4.2 Pie Chart Showing Trip purpose.................................................................................................72

Fig. 6.1 Example of An overpass..............................................................................................................84

Fig 8.2: Examples of traffic signs.............................................................................................................88

Figure 8.3 Example of Various Road signs in Kenya.............................................................................88

Changamwe-Kwa Jomvu (A109A) x May 2023

LIST OF ABBREVIATIONS

A

AADT- Average Annual Daily Traffic

AASHTO - American Association of State Highway and Transportation Officials

ADT - Average Daily Traffic

C

CADD - Computer Aided Design and Drafting

CL - Centre line

CWW - Carriageway width

D

DHV - Daily Hourly Volume

DV - Design vehicle

E

ELEV. - Elevation

F

FG. – Final Grade

FFS – Free flow Speed

H

HOR. - Horizontal

K

KeNHA - Kenya National Highways Authority

KeRRA - Kenya Rural Roads Authority

KURA - Kenya Urban Roads Authority

KWS - Kenya Wildlife Service

L

LOS - Level of service

LW - Lane width

LHS – Left hand Side

M

MoR - Ministry of Roads

N

Changamwe-Kwa Jomvu (A109A) xi May 2023

NMT – None Motorized Transport

O

OGL – Original Ground Level

P

PSD - Passing Sight Distance

R

ROW - Right-of-way

RRW - Road reserve width

RHS – Right hand side

S

S - Shoulder

SISD - Safe Intersection Sight Distance

SSD - Stopping Sight Distance

T

TRL - Transport Research Laboratory

TRRL - Transport and Road Research Laboratory

V

VETR. - Vertical

Changamwe-Kwa Jomvu (A109A) xii May 2023

Chapter 11. INTRODUCTION 1.1 General Overview of the subject.

The geometric design of highways deals with the dimensions and layout of visible features of the

highway. The features normally considered are the cross section elements, sight distance consideration,

horizontal curvature, gradients, and intersection. The design of these features is to a great extend

influenced by driver behaviour and psychology, vehicle characteristics, traffic characteristics such as

speed and volume. A proper geometric design will help in the reduction of accidents and their severity.

The planning cannot be done stage wise like that of a pavement, but has to be done well in advance.

The road starts at Changamwe roundabout through to Kwa Jomvu making an important junction with the

road to Mombasa International Airport, a road to the oil refinery which connects the Magongo area,

another gravel road to Miritini estate, crosses railway line immediately after this before it joins with A109

road at Kwa Jomvu. The road is of bitumen standards.

1.2 Background Highway geometry should be designed for vehicle traffic safety and efficiency, particularly on the trunk

roads or Expressways on which traffic function must be most important. It can be estimated that more

than 50% of road fatalities can be attributed to accidents that occur on two-lane roads outside built-up

areas, and at least half of them can be attributed to those that occur on curved roadway sections.

These estimations are supported by the results of (Brinkman, 1984) who reported that horizontal curves

are ranked with intersections as the most likely Locations for accident concentration on two-lane rural

highways. Thus, curved sites represent one of the most important critical locations for answering the

question, “where do people die”, and for considering measures to reduce accident frequency and severity.

For this reason, two-lane rural safety is considered to be one issue of pressing national concern in both

Europe and the United States.

Multilane highways, on the other hand, are much safer. For example, the U.S. Interstate system and the

comparable German Autobahn system, with about 10% of the total number of fatalities, represent the

safest road class, even though 25% of the vehicle kilometers driven are normally done on these roads.

Thus, multilane highways are normally designed very generously. That means that curvilinear aspects are

more or less included in the design of those roads (Lamm, 1994)

Changamwe-Kwa Jomvu (A109A) 1 May 2023

1.3 Management of the Road Networks in Kenya. Road Infrastructure is a key driver to development of Nations. The Kenya Vision 2030 aspires for a

country firmly interconnected through a network of roads, railways, ports, airports, water ways and

telecommunications as well as adequately provided with energy.

Road transport is the predominant mode of transport and carries about 93% of all cargo and passenger

traffic in the country. Kenya’s road network has been established to be 160,886 km long. About

61,936km of these roads are classified while the remaining 98,950km are not classified. (Source: Kenya

Road Board, 2014)

Responsibility for the management of the road network falls under the Ministry of Roads and

implemented through Kenya National Highways Authority (KeNHA), Kenya Rural Roads Authority

(KeRRA), Kenya Urban Roads Authority (KURA) and Kenya Wildlife Service (KWS)

1.4 The Study Area. Increased traffic demand and the need for improved mobility in Changamwe area was resulting from

commercial and residential growth. In order to assess these conditions and begin to identify appropriate

solutions in Changamwe Area, the Changamwe Magongo Road Design was initiated. The Design

addressed the segment of Magongo Road from the junction at Kwa Jomvu to the roundabout, a distance

of approximately five kilometres.

The Vicinity Map of the study area is shown in Figure 1.1 and 1.2.


Figure 1.1 Changamwe-Magongo site location map

(Source: SAMU Engineering Consultants Ltd, 2012)


Figure 1.2 The study area in detail

(Source: Google maps)

Where the highlighted areas in the map represent:

I. Changamwe round about (junction of A109 and A109A towards Mombasa) Port Reitz Junction

through Magongo mainland to Kwa Jomvu.

II. Airport junction (lies along A109A en route to airport).

III. Refinery junction (lies along A109A en route to refinery).

IV. Kona Relly (lies at the junction heading to Miritini and Magongo estates).

V. Kwa Jomvu (junction of A109 and A109A towards Nairobi).

1.5 Problem Statement. The increase in the freight transportation has induced a transportation management problem along the

Changamwe Magongo Road. This being in the form of increased heavy good vehicles which are

generally slow hence leading to congestion.


Development of container depots as well as cargo handlers along the road is also taking place. The effect

of this is that, as the heavy vehicles turn to access these facilities, they cause more congestion and

unprecedented damage to the road facility.

Truck parking along the road has risen in number thus reducing the effective carriageway. The Road

segment at Kwa Jomvu where the dual carriageway from Mombasa ends has ultimately contributed to the

increased pressure on the road facility where most passengers opt to use motorcycles for the short

distance trips and avoid Matatus and small buses which cannot move through the jammed traffic.

1.6 Objectives and Scope of the Study. The Changamwe Magongo Road serves rural, urban and international traffic. It links the international and

local travels occurring in Mombasa International Airport while at the same time links the rural travels

particularly between Magongo and the city of Mombasa. The objective of the geometric design was for

optimum efficiency in traffic operation and maximum safety at reasonable cost where Highway

alignment, road classification and Pavement surface characteristics were analysed.

1.7 Limitations A major limitation in carrying out the exercise was data collection as seeking data from the relevant

authorities was involving and hence time management was crucial in finishing the project report and

drawings.

1.8 Study Methodology. This describes the systematic, theoretical analysis of the methods applied so as to be able to achieve the objectives of the study mentioned earlier.

a) Literature Review

Its purpose is to convey the knowledge and ideas that have been established on geometric design so as to ensure its efficiency. All information was obtained from published works and design manuals.

b) Data collection and analysis

This describes the means by which transportation data is collected, collated and analyzed by a transport engineer to enable him to do the geometric design of a roadway effectively.

The different surveys done to collect traffic data include:-

I. Traffic censuses

A traffic census is carried out to determine the characteristics of the traffic moving along the road e.g.

i. The volume of traffic flowii. The type of vehicles e.g. Lorries, cars etc.


iii. The speed of the vehiclesiv. Pedestrian behavior and use of the road

This can be achieved by stationing observers at strategic points along the road at peak hours especially morning hours.

II. Pedestrian studies

This involves collection of data on the available pedestrian facilities e.g. traffic signals and foot paths

III. Topographical survey

It involves the process of ascertaining and representing upon a plane surface the contour, physical features etc. of any portion of the surface of the earth.

Measurement of the terrain features can be carried out using the Total Station equipment.

c) Geometric Design

It is concerned with the positioning of the physical elements of a roadway according to standards and constraints. Reference was made to Road design manuals as a guideline to the road standards in Kenya to provide the drawings.


Chapter 2

2. LITERATURE REVIEW 2.1 The Road System 2.1.1 Road Classification

A road classification system has several purposes which are interrelated. The application of a road

classification provides a framework for policy formulation in road administration and management. Road

classification assists planners in allocating resources for maintenance and development for the road

network between different groups of roads and also for setting priorities. A road classification system

indicates an expected level of service for specific road classes and therefore provides guidance to design

engineers in applying appropriate design standards and also clarifies responsibilities amongst road

administrations and the assignment of road sub-networks.

A well-defined and consistent road classification system influences road user expectations, behavior and

performance in traffic which improves the effectiveness with which the road network carries traffic.

Hence the road classification system should provide road users with some confidence in the level and

continuity of service intended to be provided.

Road classification based on speed and accessibility is the most generic one as the accessibility of road

increases, the speed reduces. (See figure 2.1).

Figure 2.1. Speed vs Accessibility

(Source: Rao, 2006)


Accordingly, the roads can be classified as follows in the order of increased accessibility and reduced

speeds:

I. Freeways: Freeways are access controlled divided highways. Most freeways are four lanes, two

lanes each direction, but many freeways widen to incorporate more lanes as they enter urban

areas. Access is controlled through the use of interchanges, and the type of interchange depends

upon the kind of intersecting road way (rural roads, another freeway etc.)

II. Expressways: They are superior type of highways and are designed for high speeds (120 km/hr is

common), high traffic volume and safety. They are generally provided with grade separations at

intersections. Parking, loading and unloading of goods and pedestrian traffic is not allowed on

expressways.

III. Highways: They represent the superior type of roads in the country. Highways are of two types-

rural highways and urban highways. Rural highways are those passing through rural areas

(villages) and urban highways are those passing through large cities and towns, i.e. urban areas.

IV. Arterials: It is a general term denoting a street primarily meant for through traffic usually on a

continuous route. They are generally divided highways with fully or partially controlled access.

Parking, loading and unloading activities are usually restricted and regulated. Pedestrians are

allowed to cross only at intersections/designated pedestrian crossings.

V. Local streets: A local street is the one which is primarily intended for access to residence,

business or abutting property. It does not normally carry large volume of traffic and also it allows

unrestricted parking and pedestrian movements.

VI. Collector streets: These are streets intended for collecting and distributing traffic to and from

local streets and also for providing access to arterial streets. Normally full access is provided on

these streets. There are few parking restrictions except during peak hours.

Road Classification in Kenya

The Current Road Classification System in Kenya was developed over 30 years ago and has six road

classes named from Classes A to E and a Special Purpose Road class (SPR). Each class is defined by the

functional criteria related to administrative level of centers the roads connect. The system covers only

61,936km of the entire road network of 160,886km while the rest 98,950km are not classified. (Source:

Kenya Road Board, 2014)


Table 2.1 Current Road Classification

(Source: Kenya Road Board, 2014)

Table 2.2 Summary of Current Road Classification in Km

ROAD CLASS PAVED UNPAVED TOTALA 2,772 816 3,588B 1,489 1,156 2,645C 2,693 5,164 7,857D 1,238 9,483 10,721E 577 26,071 26,649

SPR 100 10,376 10,476U 2,318 96,623 98,941

TOTAL 11,189 149,689 160,886(Source: Kenya Road Board, 2014)


CLASS DESCRIPTION FUNCTIONA International Trunk

RoadsLink centers of international importance and cross international boundaries or terminate at international ports or airports (e.g. Mombasa,)

B National Trunk Roads

Link nationally important centers (e.g. Provincial headquarters)

C Primary Roads Link provincially important centers to each other or to higher class roads (e.g. District headquarters)

D Secondary Roads Link locally important centers to each other, or to more important centers or to a higher class road (e.g. divisional headquarters)

E Minor Roads Any link to a minor centerSPR G

LRST

W

Government RoadsSettlement RoadsRural Access RoadsSugar RoadsTea RoadsWheat Roads

U Unclassified All other public roads and streets

2.1.2 Control of Access

Access control is the regulation of access, through the limitation of public access rights to and from

properties adjacent to the highway facility. The principal advantages of control of access are the

preservation of a high quality of traffic service and improved safety.

Access control is an important consideration in highway planning, design, and operation. Some degree of

access control should be included in the development of any major highway, particularly where mobility

is important. The degree of access control should be balanced among three essential public functions

which are access to property, travel mobility and safety of the motorist.

Uncontrolled access to roadside development along roads, 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, whereby the right of owners or occupants of

land to access is controlled by the Highway Authority.

The reason why access control improves safety is because there are fewer unexpected events caused by

vehicles entering and leaving the traffic stream at slower speeds, resulting in less interference with

through traffic. (Source: Hoel, 2009)

Control of access is usually classified into three types for its degree of control, namely:

I. Full control - where preference is given to through traffic by providing access connecting with

selected public roads only and by prohibiting crossings at grade or direct private driveway

connections

II. Partial control - where preference is given to through traffic to a degree that in addition to access

connection with selected public roads, there may be some cross trafficked roads. At grade

intersections access should be limited and only allowed at selected locations.

III. Non-controlled or unrestricted access - where preference is given to local traffic, with the road

serving the adjoining areas through direct access connections.

To compensate for the limited access to roads with full or partial control of access, frontage or service

roads are sometimes attached to the sides of the main roads 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. In Non Control Access there are basically no access

limitations. (MINISTRY OF ROADS, 2009 (Draft Manual))


Road function determines the level of access control needed. Motorways should always have full control

of access. The following general guidelines are given for the level of access control in relation to the

functional road classification:

Table 2.3: Level of rural access control

Functional Class Desirable Reduced

Major Arterial Full Full

Minor Arterial Partial Partial

Major Collector Full or Partial Partial

Minor Collector Partial Unrestricted

Major Local Partial or unrestricted Unrestricted

Minor Local, Local Access Unrestricted Unrestricted

(MINISTRY OF ROADS, 2009 (Draft Manual))

Table 2.4: Level of urban access control

Functional Class Desirable Reduced

Major Arterial Full Partial

Minor Arterial Full or Partial Partial

Major Collector Partial Partial

Minor Collector Partial Unrestricted

Major Local Unrestricted Unrestricted

Minor Local, Local Access Unrestricted Unrestricted


The Changamwe Magongo Road is an urban minor arterial road therefore its level of access is Full or

Partial.

2.1.3 Road Reserve (Right-of-way)


It is the strip of land acquired by the road authority for provision of a road or highway. Land availability

is of particular importance in urban areas. Land for the road reserve may be restricted because of the

existence of major buildings, high cost of acquisition or other protected land use.

During the planning process, it is prudent to attempt to acquire additional road reserve width to allow for

improvements to traffic operations, auxiliary lanes, wider pedestrian areas, cycle paths as well as for

provision of utilities, streets aping and maintenance considerations. This should, however, not be taken to

the extreme, where large tracts of land are unnecessarily sterilized in anticipation of some or other future

eventuality. (South African National Road Agency, 2000)

The location of existing major utilities, which may be either above or below ground, and difficult or

costly to relocate is a fairly common design control in urban areas. In particular the location of

aboveground utilities in relation to clear zone requirements should be carefully considered.

Road reserves are provided in order to accommodate future road connections or changes in alignment,

road width or junction layout for existing roads and to enhance the safety, operation and appearance of

the roads. The road reserve should always be determined and shown on the final design plans for road

projects. (MINISTRY OF ROADS, 2009 (Draft Manual))

The figure below represents the Cross-section elements of a road reserve:


Figure 2.2. Road Reserve

(South African National Road Agency, 2000)

The following road reserve widths are applicable for the different rural road classes:

Table 2.5: Rural road reserve width

Functional Class Road reserve width (m)

Major Arterial 40 -60

Minor Arterial 40 -60

Major Collector 40

Minor Collector 25

Major Local 9 – 20

Minor Local 9 – 10

Local Access 9 – 10


The reduced widths should be adopted only when it 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 costs 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 road reserve boundary should be at a distance from the centerline of the nearest

carriageway equal to half the road reserve width for single carriageway roads.


Table 2.6: Urban road reserve width

Functional Class Road reserve width (m)

Major Arterial 60 – 80

Minor Arterial 20 – 45

Major Collector 18 – 40

Minor Collector 15

Major Local 12 – 15

Minor Local 9 -12

Local Access 9 -12


Road reserves in urban areas should be treated in conformity with the city master plans that indicate

future land use developments. In such cases, the following given values can be used as a general

guidelines. However, the design engineer after a careful comparison of reserve values with the master

plan can make revision to cater safe, economical, and environmental sound design.

2.1.4 Topography, and Physical features

These affect the geometric design as it is easier to construct roads with required standards for a plain

terrain. However, for a given design speed, the construction cost increases multiform with the gradient

and the terrain. Therefore, geometric design standards are different for different terrain. This keeps the

cost of construction and time of construction under control and is characterized by sharper curves and

steeper gradients. The aesthetics of the region should not be affected and this mainly depends on how the

land is used e.g. in excavation.

2.1.5 Environmental Considerations

Construction of a highway at any location will have a significant impact on its surroundings. A highway

is therefore an integral part of the local environment and must be considered as such. This environment

includes plant, animal, and human communities and encompasses social, physical, natural, and man-made

variables. These variables are interrelated in a manner that maintains equilibrium and sustains the lifestyle

of the different communities. The construction of a highway at a given location may result in significant

changes in one or more variables, which in turn may offset the equilibrium and result in significant

adverse effects on the environment. This may lead to a reduction of the quality of life of the animals

and/or human communities. It is therefore essential that the environmental impact of any alignment

selected be fully evaluated.


2.1.6 Traffic Generation Demand and Forecasting

Travel Demand Forecasting (TDF) is a valuable tool for the long range planning of the transportation

system. The main purpose for doing TDF is to quantify the amount of travel on the transportation system.

The demand for transportation is created from the general growth of a community, major developments

and other activities like recreation and tourism. The supply of transportation system is represented by the

planned road network, intersections performance, and roadway capacities.

There are four basic steps in the Travel Demand Forecasting methodology:

I. Trip Generation – This is the first step in conventional modelling. This step converts the

demographic/land use data into number of trips.

II. Trip Distribution – This second step converts the trip generation data into trip table(s) containing

the number of trips going from one growth area to other area.

III. Mode Choice – This third step allocates the person trips from trip distribution to available modes

based on a set of factors (i.e., availability of public transit, accessibility, and travel time).

IV. Trip Assignment – The assignment process places the total vehicle trips as estimated travel

demand on each link identified in the major roadway network.

2.1.7 Road Capacity

The term capacity is used to express the maximum hourly rate at which persons or vehicles can

reasonably be expected to traverse a point or uniform section of a lane or a carriageway during a given

period of time under prevailing carriageway and traffic conditions. The design of main traffic routes in

built-up areas should be based on peak-hour demands and not, as in rural areas, on the average daily

traffic. Due allowance should be made, especially in intersection design, for tidal flows during the

morning and evening peaks and for any other peaks during the day as, for example, at lunch time.

Guide values for rural road capacities is given in Table 2.7 below:

Table 2.7: Practical capacities of two-way rural roads


Basic capacity for a2-lane single carriageway (pcu/h)

OperatingSpeed(km/h)

DesignSpeed(km/h)

Proportion of road with pass.sight dist. greater than minimum requirement

DesignCapacity(pcu/h)

2000 95 110-120 100%

80%

60%

400

360

3002000 80 90-100 100%

80%

60%

40%

800

700

600

480

2000 65 80 100%

80%

60%40%

1120

1060

94n760

2000 55 70 100%

80%

60%

40*

1340

1240

1140

1040(MINISTRY OF ROADS, 2009 (Draft Manual))

Approximate practical capacities of urban roads between junctions are given in Tables 2.8 and 2.9, which

cover a wide range of carriageway widths typical of both new and existing roads. On two-way

carriageways capacity is relatively independent of distribution by direction and designs can be based on

two-way flows; on the other hand, on dual or divided carriageways capacity is dependent on distribution

by direction and designs must therefore be based on peak-hour flows in the busier direction of travel.

Table 2.8: Practical capacities of two-way urban roads


Effective width of carriageway in meters (excluding refuges or central

2-iane 3-lane 4-lane 6-lane

7.0m 7.3m 10m 14m 20m Remarks

Description Capacity in pcu's per hour for both directions of flow

Capacity in pcu's per hour for one direction of flow

All-purpose roads with no frontage access, no parked vehicles permitted and

1350 1500 2200 2 200 3300 Appropriate to all- purpose distributors

All-purpose streets with high capacity junctions and 'No waiting' restrictions

1000 1200 1800 1 350

2250 (or2450 for dual carriagewayy

Applicable to distributors and access roads where accesses is frequent but capacity is not unduly restricted by junctions

All-purpose streets with capacity restricted by parked vehicles and junctions

450 to600

600 to750

1100 to1300

900 to1000

1500 to2000

Applicable to roads waiting vehicles and with heavy cross traffic limit capacity


Table 2.9: Practical capacities of one-way urban roads


Effective width of carriageway inmeters ( excluding refuges or central reservation)

2-lane 3-lane 4-lane

7.0m 7.3m 10m 14m Remarks

Description Capacity in pcu's per hour

Urban motorways with grade separation and no frontage access

3000 4500 (11m)

6000(14.5m)Applicable to the highest of category of distributor

All-purpose roads with no frontageaccess, no standing vehicles andnegligible cross

2200 2400 3300 4400Applicable to all- purpose distributors

All-purpose streets with high capacity junctions and 'No waiting' restrictions

1450 1600 2400 3350

Applicable to distributors and access roads where access is frequent but capacity unduly restricted by junction

All-purpose streets with capacity restricted by parked vehicles and

950 1100 1800 2800

Applicable to roads waiting vehicles and with heavy cross traffic limit capacity


2.1.8 Level of Service


Level of Service relates to the operating conditions encountered by traffic. It is a qualitative measure of

factors such as speed, trip time, interruptions, interference, freedom to overtake, ability to manoeuvre,

safety, comfort, convenience and vehicle operating costs. The choice of level of service shall generally be

based on economic considerations.

Six levels of service are defined. These vary from level A which is the free flow condition, where

drivers can maintain their desired speed (low volume and high speed); to level F where the traffic is

approaching saturation with drivers traveling at low speed due to high volume of traffic.

The maximum volume that can be carried at any selected level of service is referred to as the service

volume for that level. The traffic flow rates that can be served at each level of service are termed as

service flow rate. Once a level of service has been identified as applicable for design, the accompanying

service flow rate logically become the design service flow rate, implying that if the traffic flow rate using

the facility exceeds that value, operating conditions will fall below the level of service for which the

facility was designed. (MINISTRY OF ROADS, 2009 (Draft Manual))

Figure 2.3: Linkage between level of service (LOS), speed and flow/capacity.

(Rogers, 2003)

2.1.9 Design speed


Speed is a primary factor in all modes of transportation and geometric design of roads. The speed of vehicles on a road depends, in addition to capabilities of the drivers and their vehicles, upon general conditions such as the physical characteristics of’ the highway, the weather, the presence of other vehicles and the legal speed limitations.

Operating speed is the highest overall speed at which a driver can travel on a given road under favorable weather conditions and under prevailing traffic conditions without at any time exceeding the design speed on a section by section basis.

Design speed is the maximum safe speed that can be maintained over a specified section of the road when conditions are so favorable that the design features of the road governs. The assumed design speed should be a logical one with respect to the topography, the adjacent land use and the type of road. Every effort should be made to use as high a design speed as practicable whilst maintaining the desired degree of safety, mobility and efficiency.

The proposed design standard is classified into seven groups (DR1, DR2, DR3, DR4, DR5, and DR6) for Kenyan rural road and into six groups for Kenyan urban areas namely (DU1, DU2, DU3, DU4, DU5, DU6 and DU7). These are in descending order of design hierarchy.

Each proposed design standard is generally applicable to the road types as follows:

a) Standard DR1/DU1: Provides the highest geometric design standard for rural or urban areas. Roads of this standard usually service long trips with high speed of travelling, comfort and safety. It is always designed with divided carriageway and with full access control.

b) Standard DR2/DU2: Also provides high geometric standards and suitable for long to intermediate trip lengths with high to medium travelling speeds. The road has usually with partial access control.

c) Standard DR3/DU3: Provides medium geometric standard road and suitable for intermediate trip lengths with medium travelling speeds and partial access control.

d) Standard DR4/DU4: Provides low geometric standard and serves mainly local traffic. There is partial or no access control.

e) Standard DR5/DU5: Provides the lowest geometric standard road with two-way flow. This standard is used for roads accommodating local traffic with low volumes of commercial traffic.

f) Standard DR6/DU6: Provides for a road with very low geometric standards and is applied to very low traffic volume. It is used for urban areas where two way traffic is not required.

g) Standard DU7: Provides for a road with low geometric standard with a gravel surfacing carrying a low traffic. The need for provision for two way traffic is very low.

Table 2.10 and Table 2.11 indicate the selection of design speeds for rural and urban roads respectively.

Table 2.10: Recommended Design Speed (Rural)


Design Standard Design speed ( km/hr)

Flat Terrain Rolling Terrain MountainousDR1 120 90 70

DR2 110 90 70DR3 110 85 60DR4 80 65 50DR5 80 65 50DR6 50 40 30


Table 2.11: Recommended Design Speed (Urban)

Design Standard Design Speed ( km/hr )

Urban Type I Urban Type IIDU1 90 70DU2 60 50DU3 50 40DU4 50 40DU5 50 40DU6 50 40DU7 50 40


Note:

a. Urban Type I - Relatively free in road location with very little problem as regards to land

acquisition, affected building. Such as small towns, and less dense areas.

b. Urban Type II - very restrictive in road location with problem as regard land acquisition, affected

building. Such as big towns and densely populated areas.

c. Flat Terrain - The topographical condition where highway sight distances, as governed by both

horizontal and vertical restrictions are generally long or could be made to be so without

construction difficulty or expense. The natural ground cross slopes perpendicular to natural

ground contours in a flat terrain are generally below 5%.

d. Rolling Terrain - The topographical condition where the natural slopes consistently rise above

and fall below the road or street grade and where occasional steep slopes offer some restrictions to


normal horizontal and vertical roadway alignment. The natural ground cross slopes perpendicular

to contours in rolling terrain is generally between 5 - 20 %.

e. Mountainous Terrain - The topographical condition where longitudinal and transverse changes

in the elevation of the ground with respect to the road or street are abrupt and where benching and

side hill excavation are frequently required to obtain acceptable horizontal and vertical alignment.

The naturals ground cross slopes perpendicular to contours in mountainous terrain are generally

above 20 %.

2.1.10 Design Vehicles

Both the physical characteristics and turning capabilities of vehicles are controls in

geometric design. Vehicle characteristics and dimensions affecting design include power to

weight ratio, minimum turning radius and travel path during a turn, and vehicle height and

width. The road elements affected include the selection of maximum gradient, lane width,

horizontal curve widening, and junction design.

The present vehicle fleet in Kenya includes a high number of four-wheel drive utility

vehicles and trucks. Until more detailed information becomes available regarding the

makeup of the vehicle fleet in Kenya, the four design vehicles indicated in Table 2.12

should be used in the control of geometric design until a major change in the vehicle fleet

is observed and detailed information on the different vehicle types using the roads in Kenya

becomes available.

Table 2.12: Dimension of Design Vehicle

Overall (m) Overhang(m) W he

el

base

M i n i M

ini m

u


DesignVehicle type

(m) mum

de

sign tu

rnin

g ra

dius

m in

side

ra

dius

(m)

Hei

ght

wid

th

Leng

th

Fron

t

Rea

r

4 x 4passenger car 1.3 2.1 5.8 0.9 1.5 3.4 7.3 4.2

Single unittruck 4.1 2.6 9.1 1.2 1.8 6.1 12.8 8.5

Single unit bus 4.1 2.6 12.1 2.1 2.4 7.6 12.8 7.4

Semitrailercombination 4.1 2.6 16.7 0.9 0.6 6.1 & 9.1 13.7 5.8

InterstateSemitrailer 4.1 2.6 21.0 1.2 0.9 6.1 & 12.8 13.7 2.9

The maximum turning paths for different vehicles are shown in Figures 2.4, 2.5 and

2.6 (MINISTRY OF ROADS, 2009 (Draft Manual))

Figure 2.4: Dimensions and Turning Radius for a Single Unit Truck


Figure 2.5: Dimensions and Turning Radius Path for Single Unit Bus


Figure 2.6: Dimensions and Turning Radius for a Semi-Trailer Combination (15m overall) also Applicable for Truck (Tandem) Plus Trailer.



2.2 Sight Distance Sight distance is a fundamental criterion in the design of any road, be it urban or rural. It is essential for

the driver to be able to perceive hazards on the road and to have sufficient time in hand to initiate any

necessary evasive action safely. On a two lane two-way road it is also necessary for him or her to be able

to enter the opposing lane safely while overtaking. In intersection design, the application of sight distance

is slightly different from its application in design for the open road but safety is always the chief

consideration.

The following sight distance concepts are applicable to geometric design:

i. Stopping Sight Distance.

ii. Meeting Sight Distance.

iii. Passing Sight Distance.

iv. Visibility Splays.

2.2.1 Stopping sight distance

Stopping Sight Distance is the distance required by a driver of a vehicle travelling at a given speed to

bring his vehicle safely to a stop before reaching an object that becomes visible on the carriageway ahead.

It includes the distance travelled during the perception and reaction times and the vehicle braking

distance.

Stopping Sight Distance is the minimum sight distance requirement for all types of road and must be

provided at every point along the road. It is the sum of two distances:

a) The braking distance (V2/254(f + g))

b) Brake reaction distance (0.278 x prt x V), where prt is perception reaction time in

seconds.

Therefore stopping sight distance is calculated combining the above:



Where:

SSD = stopping sight distance [m]

Prt = perception reaction time [sec]

V = Vehicle speed [km/hr]

f = coefficient of longitudinal friction

G = percent grade, + for upgrade and – for down grade

2.2.2 Passing Sight Distance

Most roads are two-lane two way on which vehicles frequently overtake slower moving vehicles, the

passing of which must be accomplished on a lane regularly used by the opposing traffic. Passing sight

distance for use in design should be determined on the basis of the length needed to safely complete a

normal passing maneuver.

The minimum passing sight distance for two-lane highways is determined as the sum of four distances:-

a) Distance traversed during the perception and reaction time and during the initial acceleration to

the point of encroachment on the passing lane.

b) Distance travelled while the passing vehicle occupies the passing lane

c) Distance between the passing vehicle at the end of its maneuver and the opposing vehicles.

d) Distance traversed by an opposing vehicle for two-thirds of the time the passing vehicle occupies

the passing lane (2/3 of (b))


2.3 Pedestrian Facilities 2.3.1 Footpath


All urban roads should be provided with Footpaths on both sides of the roadway and the width should not

be less than 1.5m minimum and desirable 2m. The width of the footpath should be estimated on the basis

of 0.6m for each 20-30 pedestrians per minute plus 0.5m dead space. Footpaths should have a minimum

cross fall of 2.5%.

Footpaths may be constructed from interlocking concrete blocks, stone cobbles, bricks; double seal

surface dressing, asphalt or murrain. Pre-cast concrete paving blocks of sizes more than 20x20cm are not

recommended. (MINISTRY OF ROADS, 2009 (Draft Manual))

In commercial areas, it may be prudent to increase the width of footpath depending on space availability

between the road edge and the building line. In the city center and other areas where pedestrian and traffic

volumes are high, consideration should be given to the introduction of a barrier between the traffic and

the pedestrians and providing footbridges.

2.3.2 Cycle tracks

A separate cycle track should be provided on those urban roads where pedal cycle traffic is high and also

to encourage bicycle use in traffic congested areas. The cycle track need be provided on both or one side

of the road based on the design standard and the width should not be less than 2m. Where high cycle

volumes are to be accommodated, the cycle tracks should be designed for one-way traffic. Careful

consideration needs to be given to designing the grade of the cycle tracks and to the details at road

crossing places. Cycle tracks should be separated from the trafficked road by a 2m wide verge and from

pedestrian footpaths by at least 1m. Cycle tracks may be constructed in a similar manner to the footpaths,

with the exception stone cobbles.

2.3.3 Pedestrian And Cyclist Overpasses And Underpasses (Subways)

The minimum clear width of a pedestrian bridge should be 1.8m. This width is adequate for the passage

of up to 300 people per hour and allows two wheel chairs to pass and for shared bicycle/pedestrian

bridges, the minimum width is 3.0m. Where the volumes of pedestrians and/or cyclists is high, the two

functions should be segregated and the appropriate width for each function shall be allowed.

Pedestrian underpasses are not the preferred method of providing for grade separated pedestrian

crossings. They are not favored by pedestrians and cyclists because of the potential danger posed by the

“hidden” nature of the crossing. However, it is sometimes the case that an underpass is the only

reasonable alternative. (MINISTRY OF ROADS, 2009 (Draft Manual))


Underpasses should be lit and care taken with the design to ensure that “hiding” places does not occur.

There should be a clear line of sight from one end to the other and this should preferably be available

from the adjacent street. Entrances should be free from any obstacles that may hinder visibility of

pedestrians. Access should be by means of ramps or a combination of ramps and stairs provided that

wheel chair access is fully available. The access should be designed to cater for the needs of sight-

impaired people and the necessary features incorporated to guide them. Landscaping and services should

be located so as not to obscure sight lines. High quality, vandal proof lighting will be required in

underpasses to enhance personal security.

Figure 2.7: Typical illustration of cyclist envelopes


2.3.4 Bus Bays

Bus bays are provided in order to prevent vehicles from stopping on the carriageway. The siting of bus

bays (which will also be used by minibuses and other public transport) will depend greatly upon local

conditions. The long established habits of public service and other vehicle drivers and their passengers

shall not be disregarded. Bus bays shall not be sited where visibility is restricted. Typical layouts for these

facilities are shown in Figures 2.8 and 2.9.


Figure 2.8: Simple Bus Bay Mainly for Use in Rural Areas


Figure 2.9: Bus Bay for Use in Urban Areas (Busy)


2.4 Geometric Design Element 2.4.1 General

The overall quality and appearance of a road will be determined by the quality of the alignment design

(horizontal and vertical) and its relationship to the surrounding environment. The geometry of the road

alignment is presented in three projections: the horizontal, vertical alignment and cross-section.

2.4.2 The Cross- Section

The cross section of a road is a vertical plane, at right angles to the road control line, viewed in the

direction of increasing chainage. It shows the various elements that make up the road’s structure such as

traffic lanes, auxiliary lanes such as acceleration and deceleration lanes, climbing lanes, and passing

lanes, bus bays, shoulders, side slopes and back slopes.

For urban areas, cross-section elements also include facilities for pedestrians, and cyclists. These include

curbs, Footpaths, and islands. It may also provide for parking lanes. For dual carriageways, the cross-

section will also include medians. The cross-section of urban roads usually varies along a road due to one

or more of the following:

I. Variation to accommodate wider lane widths on low radius curves and junctions


II. Widening to provide space in the median for bridge piers to support overpass structures

III. Widening to accommodate barrier systems and their associated dynamic deflection or working

width requirements

IV. Widening to provide for horizontal sight distance past obstructions such as bridges and safety

barriers

V. Changes in the number of lanes and carriageways at intersections, U-turn facilities, interchanges,

collector-distributor roads and local roads

VI. Provision for public transport

VII. Variations in the width of the border

VIII. Provision for on street parking and

IX. Use of minimum dimensions to avoid major constraints such as land use

The choice of the cross-section elements depends on a number of factors, the most important of which

are:

a) The traffic volumes which the road will have to accommodate.

b) The selected design speed.

c) The road function, i.e. the predominant type of traffic that the road serves, for example, "long-

distance" versus "access", or "heavy goods" versus "passenger cars".


2.4.3 Shoulders and Ditches

A shoulder is the portion of the roadway continuous with the carriageway for accommodation of stopped

vehicle, for emergency use and for lateral support of the pavement. Their main functions are:

a) To provide space for emergency stopping free of the traffic lane.

b) To provide space for the occasional motorist who desires to stop for various reasons.

c) To provide space to escape potential accidents or reduce their severity.

d) shoulders of adequate width contribute to driving comfort and minimizes the risk of off-

tracking from carriageway

e) Sight distances is improved in cut sections, thereby improving safety.

f) Lateral clearance is provided for signs and guardrails.

g) Structural support is given to the pavement.

h) Allows passage of traffic during blockage due to accidents


i) enables non-motorized traffic (pedestrian and cyclist) in rural areas to travel with

minimum encroachment on the carriageway;

j) To act as barrier for moisture seepage to the carriageway.

For shoulders to function effectively, they must be durable to support occasional vehicle loads, in all

kinds of weather without failure. Paved or stabilized shoulders are required to minimize such structural

failure. Paved shoulders of the strength and standard as the pavement should be considered for road

standards DR1, DR2 and DU1, DU2.Gravel and earth type of roads, strength of shoulders shall be

improved on steep gradients to prevent erosion. All shoulders shall be sloped sufficiently to drain

carriageway surface water. (MINISTRY OF ROADS, 2009 (Draft Manual))

2.4.4 Medians

A median is the strip of road that separates opposing travelled ways. Medians are provided on all dual

carriageway roads such as urban Major and Minor Arterials roads and International trunk roads. Medians

have the following advantages:

(i) Significantly reduce the risk of collision with opposing traffic (clear zone principle).

(ii) Provides space for median barriers, street lighting, landscape planting, traffic signals, underground

utility lines, overpass piers, skylights to pedestrian underpasses, visibility offset on horizontal

curves, direction and regulatory signs and for public transport (HOV lanes and bus stops, and light

rail track sand platforms when required) and space for future additional traffic lanes.

(iii) Improve capacity by restricting access to property and minor side streets.

(iv)Provide a safety refuge for pedestrians making it easier and safer to cross busy roads

(v) Prevent irregular U-turn movements and Accommodate glare screening(vi)Provide a space to collect run-off from the road and carry the water to the drainage system.

If an existing road is being upgraded and the road reserve is constrained, then consideration may need to

be given to a cross section without a median. However, if a median can be included by reducing the width

of other cross sectional elements such as traffic lanes and Footpaths, this may be preferable. The use of a

variable median width should be considered where the road reserve is narrow and it is not feasible to

widen it in some areas. (MINISTRY OF ROADS, 2009 (Draft Manual))

2.4.5 Headroom and Clearances

The standard minimum headroom or clearance under bridges or tunnels shall be 5.3m and desirable is

5.5m for all classes of roads. This clearance should be maintained over the carriageway(s) and shoulders.


Where future maintenance of the carriageway is likely to lead to a raising of the road level, then an

additional clearance of up to 0.1m may be provided. Where the existing headroom exceeds the standard

minimum and a reduction would affect local industry, and then a greater clearance may exceptionally be

justified. The minimum headroom or clearance over cycle tracks and Footpaths shall be 2.20m.

The minimum horizontal clearance between the carriageway edge and the face of an abutment or pier

shall generally be 1.50m where in exceptional cases this standard may be reduced to 1.00m. The

minimum horizontal clearance between the edge of a cycle track and footpath and the face of a structure

shall be 0.25m. (MINISTRY OF ROADS, 2009 (Draft Manual))

2.4.6 Horizontal Alignment

The horizontal alignment is the plan view of the road and it is a combination of:

i. the straight or tangent

ii. the circular curve

iii. the transition curve or spiral, and

iv. Super elevation

I. The Straight

From an aesthetic point of view, the straight may often be beneficial in flat country but rarely in rolling or

mountainous terrain. However, long straights increase the danger from headlight glare and usually lead to

excessive speeding. Overtaking opportunities must however be provided at reasonable intervals and

straights are often the most appropriate solution.

The following guidelines apply for the lengths of straights:

1. straights should not have lengths greater than (20 x VD ) meters (VD in km/h)

2. Straights between circular curves following the same direction should not have

lengths less than 200m to allow super elevation run-off.


II. The Circular Curve

The minimum radius of a horizontal curve for a given design speed can be determined from the formula

given below:


Where:

VD = design speed (km/h)

e = Maximum super elevation (%)

f = side friction coefficient.

Values of “f” for rural and urban roads accepted super elevation rates are given in Tables 2.13 and 2.14.

(AASHTO, 2001)


(Rural roads).

VD (km/h) 40 50 60 70 80 90 100 110 120 130

Rmin (m) 55 90 135 195 250 335 435 560 755 950

f 0.17 0.16 0.15 0.14 0.14 0.13 0.12 0.11 0.09 0.08

(AASHTO, 2001)


(Urban Streets).

VD (km/h) 30 40 50 60 70 85 100 120

Rmin (m) 30 50 85 125 175 270 395 630

f 0.17 0.17 0.16 0.15 0.14 0.14 0.12 0.10

(AASHTO, 2001)

Side friction coefficients are dependent on vehicle speed, type, condition and texture of roadway surface,

weather conditions, and type and condition of tires. Values for minimum radius for other applicable super

elevation rates can easily calculated using the equation given above.

III. The Transition Curve

A transition curve or spiral is sometimes used in horizontal alignment design to provide a

gradual and smooth transition between tangent sections and circular curve sections or

between two circular curves.

The purpose of introducing transition curves is to provide a length over which super


elevation run-off and/or transition for widening is applied. In some cases, to improve

appearance such as on a bridge where a rigid handrail follows the exact geometry of the lane

and aesthetics of circular curves that are visible at the end of a long straight.it also provides a

length over which smooth steering adjustment can be made, especially between reverse

curves.

Generally, the Euler spiral, which is also known as the Clothoid, is used in the design of

spiral transition curves. The radius varies from infinity at the tangent end of the spiral to the

radius of the circular arc at the end that adjoins that circular arc.

The equation for applicable Clothoid transition curve is:

Where:

A = Clothoid Parameter

R = Radius at the end of the Clothoid

L cl = Lengths of the Clothoid

Figure 2.10: Clothoid elements


R = final radius Δ= circular shift

T= direction change Tl = long tangent

Tk =short tangent Ym = center Y-coordinate

X = final clothoid X-coordinate Xm = abscissa of center point


Y = final clothoid Y-coordinate

The clothoid parameter, A, expresses the rate of change of curvature along the clothoid.

Large values of A represent slow rates of change of curvature while small values of A

represent rapid rates of change of curvature.

The most rapid rate of change of curvature is represented by the minimum permissible value

of Amin. The determination of Amin is based upon considerations of the rate of change of

centrifugal acceleration, super elevation run-off, aesthetics and the ratio of the radii of

consecutive curves of a compound curve.

IV. Super elevation

One of the most important characteristics of alignment is the application of super elevation to horizontal

curves in order to counteract centrifugal forces. It is a primary feature of safety in geometric design.

Use of maximum super elevation will be considered where the radius of a curve is approaching the

minimum for the design speed; i.e. towards the minimum radius provided in Tables 3.3 and 3.4.The

practical factors limiting super elevation are weather, low speed and Vehicle characteristics such as high

center of gravity. (MINISTRY OF ROADS, 2009 (Draft Manual))

Therefore, the emax is selected based on the climate, and the likelihood of slow moving traffic.

Recommended values for values of emax:

a) The maximum super elevation for rural areas is 6%.

b) The maximum super elevation in urban areas where slow moving traffic is expected is 4%.

c) Super elevation is not recommended in urban areas where congestion is expected, and vehicle

movement is slow because of nearby junctions, traffic signals, etc.

V. Widening in curves

Pavement on horizontal curves may require widening to ensure that the operating conditions are compatible with those on tangents. Such widening in curves is required for two reasons:

Vehicles in curves occupy a greater width of carriageway since the rear wheels will track inside the front wheels.

Drivers generally experience some difficulty in holding their vehicles in the center of the lane as they shy away from the carriageway width. (MINISTRY OF ROADS, 2009 (Draft Manual))

2.4.7 Vertical Alignment


The longitudinal profile of a road consists of a series of straight grades and vertical curves. As well as

smoothing the passage of a vehicle from one grade to another, the vertical curves increase the sight

distance over crests at the junction of the grades. They should be simple in application and should result

in a design that is safe, comfortable in operation, pleasing in appearance and adequate for drainage.

For simplicity, the parabolic curve with an equivalent vertical axis centered on the vertical point of

intersection is used. Convex vertical curves are known as summit or crest curves, and concave vertical

curves as sag curves. (MINISTRY OF ROADS, 2009 (Draft Manual))

At crest curves, the minimum length may be fixed by stopping sight distance or appearance requirements.

However, lengths above the minimum may reduce the overtaking sight distance available on the

approaches. At sag curves, the length may be fixed approximately by comfort related to vertical

acceleration, appearance or, on a slightly more deterministic basis, by drainage, headlight performance or

overhead restrictions to the line of sight.

a) Maximum Gradients

Maximum gradients in relation to design speed and terrain are given in Table 2. (Hobbs, 1979). These

values should be adhered to for arterials and major collector roads where a large portion of the traffic

volume is heavy vehicles. On secondary and minor roads and other roads with little traffic the values in

Table 2.15 may be exceeded by 2%.

Table 2.15: Desirable Maximum Gradients.

TerrainMaximum gradient (%) for design speed (km/h)

40 50 60 70 80 90 100 110 120

Flat - - - 5 4 3.5 3.4 3 3

Rolling - 7 6 5.5 5 4.5 - - -

Mountainous 10 9 8 7 - - - - -


Table 2.16: Absolute Maximum Gradients.

Terrain

Maximum gradient (%) for design speed (km/h)

40 50 60 70 80 90 100 110 120

Flat - - - 6 6 5.5 5 4 4

Rolling - 9 8 7.5 7 6.5 - - -


Mountainous 12 11 10 9 - - - - -


Steeper grades produce variation in speeds between lighter vehicles and the heavier vehicles both in the

uphill and downhill directions. This speed variation leads to higher relative speeds of vehicles producing

potential for higher accident rates, lower traffic capacity and thus to increased operating cost. Maximum

gradient in itself is not a complete control as the length of a particular grade must be checked, as detailed

Section 2.5.7.3, Critical length of gradients

b) Minimum gradient

To avoid standing water in side ditches, the minimum gradient (min.g) for roads in cut sections is 0.5%.

However, flat and level gradients on uncurbed paved roads are acceptable when the cross slope and

carriageway elevation above the surrounding ground is adequate to drain the surface laterally. With

curbed roads or streets, adequate longitudinal gradients should be provided to facilitate surface drainage.

Where a flat grade is combined with super elevated horizontal curves, the rotation of the pavement may

create a situation where the flow path crosses from one side of a lane to the other, resulting in undesirable

water ponding on the pavement surface, thus, safety and proper drainage should be considered.


c) Critical Length of Grades

“Critical length of grade” is used to indicate the maximum length of a designated upgrade on which a

loaded truck can operate without an unreasonable reduction in speed. Where it is necessary to exceed the

critical length of gradient on heavily trafficked roads, it is desirable to provide either with passing

distances on the rise, or a climbing lane for heavy vehicles. Where gradients induce a reduction in speed

of 15km/hr a climbing lane shall be provided. Suggested maximum desirable and critical length of

gradients is given in Table 2.15. (MINISTRY OF ROADS, 2009 (Draft Manual))

d) Climbing Lanes

Where longitudinal gradients are long enough and/or steep enough to cause significant increases in the

speed differences between cars and heavy vehicles, both traffic safety and road capacity may be adversely

affected.

The following guidelines are to be used to determine whether the effects of such gradients will be

sufficiently severe to warrant the design and provision of climbing lanes:-


i. Climbing lanes will not be required on roads with A.A.D.T. < 2000 p.c.u. in Design Year 10,

ii. Where passing opportunities are limited on the gradients, then climbing lanes must be considered

on A, B and C Class roads with traffic flows in Design Year 10 in the range 2000 p.c.u. <

A.A.D.T. < 6000 p.c.u.

iii. Climbing lanes will normally be required on roads with A.A.D.T. ≥ 6000 p.c.u. in Design Year

10.

Consideration must always be given to the balance between the benefits to traffic and the initial

construction cost. For example, in sections requiring heavy side cut, the provision of climbing lanes may

be unreasonably high in relation to the benefits and hence climbing lanes may be omitted leading to

reduced "levels of service" over such sections.

Where climbing lanes are to be provided, they shall be introduced on A Class roads when the speed of a

typical heavy vehicle falls by 15 km/h from that speed which this vehicle would maintain on a level or

downhill section of the same road. The corresponding fall in speed applicable to B and C Class roads

shall be 20 km/h and for design purposes it may be assumed that the highest obtainable speed on a level

or downhill section of road for a typical heavy vehicle will be 80% of the Design Speed or 80 km/h

whichever is the lower. (MINISTRY OF ROADS, 2009 (Draft Manual))

The climbing lane shall be terminated when the speed of a typical heavy vehicle reaches the value at

which the climbing lane was introduced. However, it must be ensured that a typical heavy vehicle will

regain this speed without creating a traffic hazard, i.e. passing sight distance must be adequate. This latter

requirement may lead to an extension of the climbing lane beyond that point determined from speed

considerations alone.

The introduction and termination of a climbing lane shall be effected by tapers of 60 metres length. The

tapers shall not be considered as part of the climbing lanes and should be located in the flatter section of

gradient before the beginning and end of climbing lane. (MINISTRY OF ROADS, 2009 (Draft Manual))

e) Vertical Curves

Vertical curves are used to connect intersecting gradients in the vertical plane and are therefore provided

at all changes of gradients to smoothen the passage of a vehicle from one grade to another and increase

the sight distance over crests at the junction of the grades. They should be of sufficiently large curvature

to provide comfort to the driver, that is, they should have a low “rate of change of grade”. In addition,

they should afford adequate sight distances for safe stopping at a given design speed. Vertical curves are


normally parabolic about the point of intersection (P.I) of the vertical tangents they join. They are thus,

according to J.H. Banks, of the form

y= yo+g1+r x2

2

For simplicity the type of curve generally used is the simple parabola whose equation is:

y=k x2

where:

y = vertical offset

k = a constant

x = horizontal distance

Traditionally, the parabola has been used because of its simplicity and because all formulae are exact

whereas the same formulae used with the circle would be approximate. Figure 11 details the above

parameters. There are three associated parameters which are radius, length, and grade difference and their

correlation is also shown. (MINISTRY OF ROADS, 2009 (Draft Manual))


Figure 2.11: Vertical curves typical geometry


Length of vertical curve is equally spaced horizontal about I.P

k= A200 L

R=100 LA

Therefore; y= x2

2 R

Where

y=elevationof a point of the curve

yo=elevationof the beginning of the curve

g1=grade just before the curve

x=horizontal distance ¿ thebeginning of the vertical curve ¿any point of the curve

r=rate of changeof grade(g1−g2)/L

g2=grade just beyond end of vertical curve

L=lengthof curve

A=the differencebetweenthe two gradients

R=equivalent radius of the vertical curve

k=rate of change of curvature

f) Minimum Radii Of Vertical Curves

Usually, the largest radii vertical curves should be used provided they are reasonably economical.

However in difficult situations, vertical curves approaching the minimum may be considered where the

cost of providing larger curves makes their use prohibitive. (MINISTRY OF ROADS, 2009 (Draft

Manual))


The following three factors control the selection of minimum radii of vertical curves:

• aesthetic or appearance

• riding comfort

• Sight distance.

2.5 Road Furniture 2.5.1 General

Road furniture represents a collection of marginal elements intended to improve the driver’s perception

and comprehension of the continually changing appearance of the road. Traffic islands, kerbs and road

markings delineate the pavement edges and thereby clarify the paths that vehicles are to follow. Safety

fences prevent cars from leaving the road at locations where this would have the most severe

consequences. Fences and gates along the road reserves are a means of controlling access.

Marker posts assist in a timely perception of the alignment ahead and, when equipped with reflectors,

provide good optical guidance at night. Traffic signs provide essential information to drivers for their safe

and efficient manoeuvring on the road. (MINISTRY OF ROADS, 2009 (Draft Manual))

2.5.2 Traffic Islands

This is the area between traffic lanes for the control of vehicle movements and which may also be used as

pedestrian refuge. Traffic islands may take the form of an area delineated by barrier kerbs or a pavement

area marked by paintings or a combination of the two. They should ideally be 2m wide and not less than

1.6m.

2.5.3 Kerbs

Kerbs are used to mark the edging of vehicle paths at junctions, bus stops or parking bays. They are also

used to protect the edge of the road from damage when ridden on by vehicles. They are made of concrete

and are constructed using standard moulds whose dimensions vary according to the function and type of

kerb.

Raised kerbs with vertical faces about 4 in. high should be provided where footways or cycle tracks lie

within about 10 ft. of the carriageway or where obstructions such as bridge piers and lighting columns are

less than 5 ft. from the carriageway.


Where footways are much used by wheelchairs, kerb heights should be reduced to about 1 in. above

channel level adjoining pedestrian crossings and other suitable crossing points. The footway should be

ramped down in an easy slope towards the lowered kerb. (Hobbs, 1979)

They normally should be light-colored and should be clearly distinguishable from other parts of the road

by day or night and in wet or dry weather.

2.5.4 Marker Posts

Marker posts are intended to make drivers aware of potential hazards such as abrupt changes in shoulder

width, abrupt changes in alignment, approaches to structure etc.

Generally, horizontal curves can be outlined sufficiently by marker posts positioned only on the outside

of a curve. Reflective surfaces or buttons on marker posts greatly improve their visibility at night and are

not intended to resist impact. Marker posts should be sited 0.25m outside the edge of the shoulder.

2.5.5 Safety Fences

A safety fence shall be provided at sections of traffic hazards, such as fixed objects along the edge of the

shoulder, steep side slopes at escarpments or along water courses etc. where the hazard of hitting the

safety fence is considered a desirable substitute for a more serious accident.

A safety fence is generally a guard rail of the flex-beam type though for low cost low volume roads,

specially designed masonry and/or concrete wall may be a more economical option.

2.5.6 Traffic Signs And Road Markings

Safety and efficiency of operation depend to a considerable degree, upon the geometric design. The

physical layout must be supplemented by effective signing and marking as a means of informing, warning

and controlling traffic. Traffic signs and road marking plans, coordinated with the horizontal and vertical

alignments, junctions, sight distance obstructions, operating speeds and maneuvers, should be prepared as

an integral part of the design process.

There are three categories of traffic signs:

a) Warning signs-identify actual or potential hazards of permanent or temporary measure e.g.

junction, bend or hill. Normally they are equilateral triangles with apex at the top, may however

be inverted to warn of a Stop or Give Way sign ahead.


b) Informatory signs-provided for the convenience of road users to improve highway operations with

regard to efficiency and safety. Most informatory signs are rectangular with pointed end added to

some direction signs.

c) Regulatory signs-these are the signs that define statutory regulations governing highway control

and operations. All the regulatory signs are circular. They are legally enforceable and are of two

categories;

Prohibitory, which instruct drivers on what they must not do e.g. no entry.

Mandatory, which instruct drivers on what they must do e.g. stop or keep left. (Hobbs,

1979)

The regulations are very extensive and quite prescriptive on the design of signs. They are:

i. Sign size and colour.

ii. What information is allowed to be displayed, particularly on warning and regulatory signs.

iii. Illumination requirements.

iv. The retro-reflectivity of materials to be used in manufacturing the sign face. (Slinn, Guest, &

Mathews)

Road markings are additional visual aids applied on pavements, kerbs, and fixed objects near a

carriageway to supplement visual information gained from road signs. All markings must be legible,

attention capturing and clear in meaning. Carriageway markings are used to:

a) Define traffic lanes.

b) Guide vehicles at junctions.

c) Indicate positions of bus stops, taxi ranks and parking bays.

d) Define carriageway edges.

e) Prohibit overtaking.

f) Indicate waiting restrictions.

The colour, durability and skid resistance of the markings are determined by the purpose of marking,

location and traffic environment. The markings should be skid resistant in both wet and dry conditions

especially where cross falls are steep and where the numbers of turning two-wheeled vehicles are

appreciable. (Hobbs, 1979)


2.6 The Project Area 2.6.1 General

Changamwe is a suburb of Mombasa, in Mombasa County, in the former Coast Province of Kenya. The area is primarily industrial, with a number of modern concrete tower blocks housing residents. Industries include refineries and various process industries.

The design road runs from the Changamwe roundabout through to Kwa Jomvu making important junction with the road to Mombasa International Airport, a road to the oil refinery which connects the Magongo area, another gravel road to Miritini estate, crosses railway line immediately after this before it joins with A109 road at Kwa Jomvu. The road is of bitumen standards.

2.6.2 Topography

The altitude varies between 49m and 60m above sea level. The road passes through a flat to rolling terrain.

2.6.3 Climate and Rainfall

The area experiences a bimodal rainfall pattern, with long rains in March-May and short rains from October-December. However a relatively wet, narrow tropical belt lies along the Indian Ocean coast. Behind the coastline large areas of semi-arid and arid desert lands stretch.

2.6.4 Geology and Soils

The soils are poorly drained, moderately deep to very deep silty sand and sandy clay soils which are highly plastic when wet and are suitable for food and plant growth.


Chapter 3

3. DATA COLLECTION 3.1 Introduction

The aim of collecting traffic data is to obtain the information that a transportation engineer scientifically analyses to plan and design for or improve concerned transportation facilities.

Data is collected by means of field studies in areas of interest depending on the purpose of a particular project and subsequently analyzed according to the intended purpose.

The study was mainly based on data obtained from the relevant authorities responsible for the construction of existing and future urban roads in Kenya i.e. Kenya National Highways Authority (KeNHA) and SAMU Engineering Consultants Ltd with permission.

3.2 DATA COLLECTION METHODOLOGY 3.2.1 Preliminaries


A reconnaissance was made of the study area to capture the difficulties experienced by both pedestrians and motorists on the road.

With these ideas in mind, a desk study was undertaken so as to come up with techniques for data collection.

Classified directional traffic counts and Origin –Destination (O/D) studies were done at survey locations and the study programme as depicted in Table 3.1;

Table 3.1: Points of Study Locations

I. Changamwe round about( junction of A109 and A109A towards Mombasa )

Manual counts – 13th December 2011 and 14th December 2011

II. Airport junction(lies along A109A en route to airport)


III. Refinery junction(lies along A109A en route to refinery)


IV. Kona Relly(lies at the junction heading to Miritini and Magongo estates)


V. Kwa Jomvu( junction of A109 and A109A towards Nairobi)

Manual counts – 17th December 2011 and 18th December 2011O/D Surveys – 15th December 2011


The points above are illustrated in Fig 1.2.

Axle Load Surveys were also conducted on the road using a mobile weigh-bridge to be able to design a

road pavement which is capable of carrying future traffic load. It also covered commodity carrying traffic

such as Medium Goods, Heavy Goods, Buses, Tractors and some Light trucks.

An assessment of journey times was made on Changamwe –Magongo - Kwa Jomvu – Miritini

(A109A).The details of this study are given in Chapter 4.

3.2.2 Topographical Survey

The survey was carried out by mapping from aerial photography. A digital terrain model was generated

from the aerial photography which was then used for generating the profile.

3.2.3 Climate and Rainfall Data

The area experiences a bimodal rainfall pattern, with long rains in March-May and short rains from October-December. However a relatively wet, narrow tropical belt lies along the Indian Ocean coast. Behind the coastline large areas of semi-arid and arid desert lands stretch.


The project area receives an annual rainfall that ranges on average between 544-1784mm in the narrow tropical belt represented by the available data for Mombasa airport. The rains are much influenced by the proximity to Indian Ocean. The movement of air masses, between the two high pressure belts in the south and north hemispheres within the inter-tropical convergence zone (ITCZ), produces the two rainfall seasons at equatorial areas.

The historical record of the annual maximum 24-hour daily rainfall in each year of record (1946-1980) for Mombasa Airport at altitude of 57 above sea level are presented below:

Table 3.2 for 12 month averages for the period under consideration.

Mombasa Moi airport Met Station - Rainfall(1971-1980)

MEAN HIGHEST LOWEST MAX. 24 HOUR RAINFALL

mm mm mm mm

38 130 1 70.2

16 90 0 49.9

55 235 1 105.7

161 601 19 119.7

236 772 36 138.9

76 182 3 59.4

67 205 5 68.0

65 216 9 74.5

74 356 0 149.9

96 328 10 104.2

95 316 4 105.4

70 172 2 68.8


Mombasa Moi airport Met Station - Rainfall(1971-1980)

MEAN HIGHEST LOWEST MAX. 24 HOUR RAINFALL

1049 1784 544 149.9


From the above table and frequency analysis, the 24hour rainfall of 2-year recurrence interval data for the

station is 149.9mm. This compared with data obtain from 2006-2010 for the Mombasa airport met station,

80.45mm 24-hour rainfall of 2-year recurrence interval for the project area was taken for design purposes.

(Refer to latest Mombasa airport Rainfall Data and Gumbel analysis - Appendix 2A).

3.2.4 Soil Characteristics

The soils along the alignment are mainly sandy silt/clay soils underlying coral gravel/shale. The soil drainage characteristics have been classified in accordance with the TRRL classification reproduced in Table 6.2. The soils along the alignment are classified under ‘Impended drainage’.

Table 3.3 Soil permeability classification.

Soil class Description

Impeded Drainage

Very low permeability.

Clay soils with high swelling potential.

Shallow soils over largely impermeable layer, very high water table.

Slightly impeded

Drainage

Low permeability.

Drainage slightly impeded when soil fully wetted.

Well drained Very permeable.

Soil with very high infiltration rates such as sands, gravels and aggregated clays.

(TRRL Laboratory Report 706, 1976)

3.2.5 Land use

Land use data was taken to indicate the various institutions along the road since they are the main traffic generators. They include:


Oil refinery Changamwe District Headquarter Changamwe Police Station Pipeline Residential Estates Hazina Container Depot Shell petrol Station Total Petroleum Station Mikindani Estates Barclays Bank of Kenya Changamwe Market Miritini Estates Changamwe Administration Police Camp

3.2.6 Inventory of the Road and Condition Survey

The road is approximately 4.9 km paved road largely made of the following construction:

Asphalt concrete Wearing course Dense bitumen binder course Brownish soft gravel base layer Yellow soft gravel sub base

A small segment of the road around km 4+000 has no binder course (Dense Bitumen Macadam). The subgrades along the alignment exhibit signs of imported material and ranges from graded crushed stone, coral stone to soft gravel. A section has rock fill for subgrade.

The road is an international road connecting Mombasa sea port to the hinterland including neighboring countries of Uganda, Rwanda, Burundi, Congo, Southern Sudan as well as Tanzania. It further serves as the main access to Mombasa international Airport as well as to the oil refinery. This road joins A109 Road at Kwa Jomvu.

The road carries a high volume of mixed traffic. It has a high volume of heavy oil tankers which go for loading at the oil refinery. The road has a number of truck parking depots.

Light goods and passenger vehicle also make a sizeable volume of daily traffic with most passenger vehicles terminating at the airport and the surrounding estates.

Other than between km 3+700 – km 4+000 and km 4+400 – Km 4+900 which have serious deformations, ruttings and general surface deterioration, the rest of the road is largely in good structural state with slight distress signs here and there including small deformations and corrugations, edge spolling, shoving etc. being observed. (Source: SAMU Engineering Consultants Ltd, 2012)

Summary of the defects is presented in table 3.4 below.

Table 3.4

No Defect Description of Defect(s) Method of Recording/ Measurement


1 Cracking Longitudinal, Transverse and Alligator cracks

Location and extents in width and length in m

2 Longitudinal Deformation

Corrugations and or undulations Location/ extents

3 Rutting Depressions along the wheel path Location/ extents

4 Patching Patched Areas. Location/ extents

5 General Deterioration of Surface

Ravelling, Peeling, Stripping, shoving

location

6 Potholes Localised depressions location

7 Spalling Erosion, breaking and spalling of Road/shoulder edges.

Location/ extents

8 Drainage Side ditch condition, condition and adequacy of existing drainage structure/s

Location and state.


3.2.7 Historical Traffic Data

Specific and significant census points have been considered to provide historical traffic flow data. These are continuous count stations on various roads whose traffic have significant effect on the project road. These points are detailed in table 3.5 below.

Table 3.5: Traffic Census point on the Trunk Road

Census Point Description

A14/23 Located East of Junction with E950 near Tiwi in Kwale District

A 14/6 An Automatic Traffic Counter located at Diani in Kwale District

A109/21

A 60-point census point

South of junction with C105 (south) in Taita Taveta District

A109/26

A continuous Count site

Northwest of Mariakani

B8/13

A continuous count station site

14 Km South of Kilifi Ferry crossing


B8/11 1 Km North of Kilifi

(Source: Ministry of Roads Traffic Census Points, 1988-2001)

Table 3.6 Historical Traffic Data Table 3.7.2 (a) A14/6

Year

Traffic by Class of Vehicle Type

Motor

CycleCar

L. Goods M. Trucks H. GoodsBus Tractor Total

P/up Matatu <3.5t >3.5t 3,4axle 5+axle

1990 976 872 570 194 6 2 13 94 - 2727

1991 962 840 799 207 3 9 17 36 - 2873

1997 1558 940 1768 153 8 28 30 55 - 4540

% Growth 9.7 8.96 -8.85 9.85 2.10 4.35


Table 3.7 (b) A14/23

Year


Motor

CycleCar



1990 784 553 374 179 11 3 29 80 - 2013

1991 792 724 338 147 4 6 16 63 - 2090

1996 843 1116 1068 194 15 4 30 32 - 3302

1997 1334 1021 1544 154 15 6 30 57 - 4161

1998 630 443 870 88 4 55 81 56 - 2227

1999 854 650 1437 108 8 3 29 28 - 3117

% Growth 1.54 4.35 -3.20 2.67 -5.70 -0.07



Table 3.8 (c) A109/21

Year


Motor

CycleCar



1989 172 232 70 178 22 61 310 92 - 1137

1991 174 47 314 146 4 94 187 112 - 1078

1992 197 232 31 170 8 66 407 40 - 1151

1995 227 287 54 125 5 63 361 104 - 1226

1996 242 244 113 161 32 132 794 86 - 1804

1997 210 298 198 166 32 111 742 173 - 1930

% Growth 7.19 2.34 2.79 6.46 3.36 4.23


Table 3.9 (d) A109/26

Year


Motor

CycleCar



1990 707 455 79 186 40 45 303 115 - 1930

1992 322 325 141 291 95 96 474 116 - 1860

1997 393 408 398 260 9 137 896 169 - 2670

% Growth -3.87 4.29 1.05 9.98 9.23 5.14



Table 3.10 (e) B8/11

Year


Motor

CycleCar



1989 315 402 125 134 9 0 12 122 - 1119

1991 229 105 266 56 9 3 3 82 - 753

1997 398 379 352 91 14 9 74 109 - 1426

1998 423 520 587 109 21 17 62 95 - 1834

% Growth 6.71 5.68 1.20 9.34 -1.60 4.67


Table 3.11 (f) B8/13

Year


Motor

CycleCar



1989 296 291 93 221 8 8 56 114 - 1087

1990 269 317 80 173 12 4 11 77 - 943

1991 336 428 98 165 12 0 57 86 - 1182

1996 268 355 378 206 8 9 111 70 - 1405

1997 768 1057 1105 331 51 41 246 165 - 3764


1998 298 416 422 96 10 9 70 130 - 1451

% Growth 2.58 4.43 1.34 4.20 2.98 3.11


Table 3.12 Average Growth in Percentage by Vehicle Class

Point CarsL.Good

M.Good

H.Good Buses

Average

A14/6 9.7 8.96 -8.85 9.85 2.1 4.35

A14/23 1.54 4.35 -3.2 2.67 -5.7 -0.07

A109/21 7.19 2.34 2.79 6.46 3.36 4.23

A109/26 -3.87 4.29 1.05 9.98 9.23 5.14

B8/11 6.71 5.68 1.2 9.34 -1.6 4.67

B8/13 2.58 4.43 1.34 4.2 2.98 3.11

Average 3.98 5 -0.95 7.08 1.73 3.57

NB: Tanker traffic were not counted separately

Thus the rate of growth of traffic within the project area can be averaged as follows:

Cycles - not considered Cars = 3.98% Light Goods = 5.00% Medium Goods = -0.95% Heavy Goods = 7.08% Bus = 1.73%

For total growths therefore, an average of 3.6, approximately 4% was adopted


Chapter 4

4. TRAFFIC STUDIES. 4.1 Classified Manual Counts.

The purpose of the survey was to collect traffic flow data in order to determine the level of usage of the

road. The data were collected in a manner which would reflect hourly and diurnal variations by

considering each vehicle type separately. Traffic survey results for the days of counts were recorded and

analyzed to give the desired Average Daily Traffic (ADT). Manual counts were done for seven (7) days

and two (2) nights, with the nights being one night on a week-day and the other on a weekend. For those

sites which were done for two (2) days only, corrective measures were established to convert them into

Average Weekly Daily Traffic (AWDT).

An absurd nature of traffic flow was observed to take place along the project, all the way to Changamwe

through Magongo.


4.2 Diurnal Variations (Motorized Traffic). Traffic flow data varied slightly from day to day as observed at the 7 day count station in Miritini. Travels

were generally heavy on Monday and Sunday and lowest on Friday and Saturday. The most average days

were on Thursday and Saturday. The results are given in table 4.1.

Table 4.1: AWDT Factors per Day per Vehicle Type

DayMotor Cycle Cars

Light GoodsLight

TrucksMedium Trucks Heavy Goods

Buses TractorAverage Per Day

Pick/up 4WD/van Matatu <3.5 t >3.5 t 3,4 Axle 5+ Axle

Mon 1.14 1.11 1.17 1.09 1.04 1.16 1.12 1.19 1.18 1.02 1.12Tue 1.24 1.17 1.15 1.13 0.91 0.79 0.69 1.20 1.02 1.22 1.05Wed 1.04 1.17 0.99 1.19 1.36 0.85 1.09 1.02 1.15 1.02 1.09Thu 0.97 0.87 0.78 0.98 0.77 0.79 1.23 0.81 1.09 1.22 0.95Fri 1.21 0.89 0.86 1.02 0.90 0.79 0.93 0.92 0.98 0.61 0.91Sat 0.80 0.73 1.19 0.87 0.90 1.10 0.79 1.21 0.90 0.87 0.94Sun 0.93 0.99 1.13 0.76 1.08 4.90 1.27 1.06 0.90 1.53 1.46AVERAGE

AWDT FACTOR 1.05 0.99 1.04 1.01 0.99 1.48 1.02 1.06 1.03 1.07


4.3 Seasonality The study period was effectively from 10th December to 19th December 2011, which is week 49/50.

The ministry of Roads has three continuous count stations located within the vicinity of the project road at Diani, Kilifi and Mariakani. These count station values have been analyzed by computing an Annual Average Value per site and divided by Weekly Average Daily traffic (AADT/AWDT). Thus traffic flow data collected are subjected to a seasonal adjustment factor for week 49/50. It is known that during the study period, coast province experiences a rather pronounced tourist traffic season. Table 4.2 depicts the seasonal factors in each station

Table 4.2: Seasonal Adjustment factor

WEEK

KILIFI

DIANI

MARIAKANI

MEAN

WEEK

KILIFI

DIANI

MARIAKANI

MEAN

1 0.89 1.00 0.91 0.93 27 1.09 1.09 1.09 1.09

2 0.92 1.10 1.01 1.01 28 1.09 0.96 1.02 1.02

3 0.97 1.07 1.02 1.02 29 1.05 0.99 1.02 1.02

4 0.98 1.01 1.00 1.00 30 1.08 1.10 1.09 1.09

5 0.96 1.02 1.02 1.00 31 0.96 0.85 0.95 0.92

6 0.97 1.08 0.94 1.00 32 0.92 0.86 0.89 0.89

7 0.97 0.90 1.07 0.98 33 0.96 0.85 0.90 0.90


8 0.98 1.17 0.96 1.04 34 0.97 0.85 0.91 0.91

9 1.00 0.93 0.91 0.95 35 0.96 0.86 0.91 0.91

10 1.00 1.02 1.01 1.01 36 0.98 0.92 0.95 0.95

11 1.02 1.03 0.97 1.01 37 1.07 0.92 1.00 1.00

12 0.98 1.04 0.96 0.99 38 1.02 0.95 0.90 0.96

13 0.95 0.98 0.96 0.96 39 1.03 1.02 1.04 1.03

14 0.97 0.97 0.97 0.97 40 1.12 0.97 1.02 1.04

15 0.95 0.96 0.95 0.95 41 1.11 0.94 1.02 1.02

16 1.01 1.01 1.01 1.01 42 1.06 0.88 0.97 0.97

17 1.11 1.16 1.17 1.15 43 1.04 0.95 0.99 0.99

18 1.13 1.29 1.30 1.24 44 1.03 0.94 0.99 0.99

19 1.21 1.39 1.30 1.30 45 1.01 1.01 1.02 1.01

20 1.16 1.30 1.27 1.24 46 1.01 1.04 1.03 1.03

21 1.18 1.24 1.21 1.21 47 1.04 1.04 - 1.04

22 1.16 1.01 1.08 1.08 48 0.99 1.04 1.01 1.01

23 1.16 1.05 1.10 1.10 49 0.91 1.07 0.99 0.99

24 1.11 1.08 1.09 1.09 50 0.70 1.19 0.94 0.94

25 1.11 1.01 1.06 1.06 51 0.70 0.99 0.89 0.86

26 1.10 1.04 1.07 1.07 52 0.71 0.99 0.85 0.85

(Ministry of roads in Kenya)

A mean seasonal factor of 0.97 is the mean used to correct all the traffic flow data from AWDT to

AADT. Fig. 4.1 depicts a plot of the above factors to give an impression of seasonality.

VARIATION OF SEASONALITY FACTORS

KILIFI

DIANI

MARIAKANI

MEAN

REF-ER-ENCE

WEEK

SEAS

ON

ALIT

Y FA

CTO

R

Figure 4.1: Seasonal variation factor (From week 1 – 52)

Discussion on Traffic Flow


Traffic flow distribution by vehicle composition is given in table 3.3 which was based on vehicle

composition and actually provided an insight into road usage. The project road was divided into THREE

segments namely:

I. Changamwe to Airport Junction (Port Reitz Junction).

II. Port Reitz Junction through Magongo mainland to Kwa Jomvu.

III. Changamwe-Kwa Jomvu.

Segment I: Traffic loading on segment one was obtained from the counts on Site No. 1 and 2

(Changamwe Round About and Airport Junction). The traffic flow on the Changamwe leg at Site No.

2 and the traffic flow on the Airport leg of Site No. 1 gave the traffic loading on this segment. This is

represented below:

M/cy CarsLight Goods

Light Truck

Medium Truck

Heavy TruckBus Tractor TotalP/UP

4WD Matatu Rigid Articulated

Changamwe to Port Reitz Junction (segment I)

4456 7790 5097 7115 885 1916 985 2191 2023 484 32943


Diagrammatic Representation of Segment I


(Source:Google maps)

Discussion on Segment I

This segment lies along the project road and has a heavy composition of passenger vehicles. The main

passenger carrier was cars with approximately 24% followed by Matatu which represent 22% of traffic by

volume on the road segment. Motorcycles, large cars/4WD were also used for the movement of people

and have higher percentages of 14 and 15 respectively. The large proportion of passenger movement on

the road project was caused by the presence of the Airport, residential estates namely Migadini, Chaani,

Magongo and Miritini on the far end of the road.

However, it was noted that the considerable number of Heavy Good vehicles, Light Good Vehicles,

Medium Good Vehicles and buses that are recorded on this road segment, were only trying to avoid the

new Nairobi road due to the congestion at Kwa Jomvu.

At one hand, some of the trucks that distribute retail goods and other related products, the rest of the

trucks were moving to the Depots along the road or to link with Nairobi road at Kwa Jomvu. The number

of motorcycles was high because of the short numerous trips they made between Changamwe and Port

Reitz junction.

On the other hand, some of the Heavy Good vehicles and tractors moved to Refinery and Port Reitz. The

tractors were used to transport empty containers while the articulated vehicles were mainly from the port

or to the port.


Segment II: Stretches from Port Reitz Junction through Magongo mainland to Kona Relly near Jomvu at

site No. 3. Traffic loading in this segment included traffic volume on the Airport junction leg at site No. 4

and Miritini leg at the same site. This is represented below:

M/cy Cars

Light GoodsLight Truck

Medium Truck

Heavy Truck

Bus Tractor TotalP/UP 4WD Matatu Rigid Articulated

Port Reitz Leg(Total)1808 2243 1223 2270 318 447 278 1064 141 153 9947

Miritini (Kona Relly) Leg 1855 2022 1169 1039 338 491 401 1694 154 185 9349Average AADT (Segment II) 1832 2133 1196 1654 328 469 340 1379 148 169 9648


Diagrammatic Representation of Segment II


Discussion on Segment II

The vehicle composition in this segment reflected a significant reduction in AADT value. This was

because most vehicles which were using segment had either branched off the channel to their areas of

interest or had simply arrived at their destinations. Most cars and Matatus branched through the Airport

road to the airport and the estates at Migadini and Chaani. Since there is still quite a number of residential

estates after the junction along the project road, the main vehicle classes on the segment were passenger


carriers. Motorcycles on this road segment represent 19%, cars 22% while Matatus 17%. In this segment,

the number of Heavy Good vehicles increased to 14%. There were short trips made between the Airport

Junction to the refinery junction by the motorcycles. The number of cars on the road were used in the

process of going and coming back from work. Heavy trucks increased because of the Refinery and those

that emerged from the Airport Road.

Segment III: Stretches from Changamwe to Kwa Jomvu at Site No. 5. The traffic on this segment is

given by the traffic at Kwa Jomvu on the Mombasa/Mikindani leg as shown in the table below:

M/Cy Cars

Light GoodsLight

TrucksMedium Trucks Heavy Goods

Buses Tractor TotalPick/ 4WD Matatu <3.5 t >3.5 t

3,4 Axle

5+ Axle

Kwa Jomvu to Changamwe (Segment III) 1693 1571 1486 2003 564 1319 509 2218 636 51 12050


Diagrammatic Representation of Segment III



Discussion on Segment III

Traffic flow on this segment was relatively even with no particular vehicle type taking up to 20%.

However the highest proportion of traffic on this road segment was goods carried with heavy trucks

taking close to 20% (18%). The number of motorcycles, about 1,200 AADT, were the ones that made the

traffic to Kwa Jomvu near the junction. The heavy trucks recorded on this leg of the junction were either

going to and from Nairobi with quite a number moving between the Depots. Passenger carrier-cars, large

cars, Matatus and buses on this road segment were headed to Miritini, Mazeras and Mariakani with some

moving out of Mombasa to far west regions. They represented 13, 12 and 17% respectively. The figures

were high due to the large extent of area they covered.

Table 4.3: Vehicle Composition per Segment by Proportion


SegmentM/cy Cars

Light GoodsLight Truck

Medium

Truck

Heavy Truck

BusTracto

r TotalP/UP 4WD

Matatu

Rigid

Articulated

Roundabout to Port Reitz (I)4456 7790 5097 7115 885 1916 985 2191 2023 484

32943

% 13.53 23.65 15.47 21.60 2.69 5.82 2.99 6.65 6.14 1.47 100

Port Reitz to Miritini (II) 1832 2133 1196 1654 328 469 340 1379 148 169 9648

% 18.99 22.11 12.40 17.14 3.40 4.86 3.52 14.29 1.53 1.75 100

Kwa Jomvu to Changamwe(III) 1693 1571 1486 2003 564 1319 509 2218 636 511205

0

% 14.05 13.04 12.33 16.62 4.68 10.95 4.22 18.41 5.29 0.42 100

4.4 Non–Motorized Traffic (NMT) Non – Motorized traffic has all along been the concern of road designs in urban areas. The project Road

traverses a heavily urban area and therefore it was necessary to conduct an NMT to be used in the

pavement design. There were a large number of pedestrians and handcarts along the road with activities in

the shops that stretched along the road.

There was heavy pedestrian traffic at Site II from Airport junction (Port Reitz junction) to Changamwe.

The survey point was located at site no. II and NMT surveys were done from 7.00 am to 7.00 pm per

direction using the following classifications:

Pedestrian

Pedal cycle rider

Hand-carts

Studies were conducted for traffic travelling along the road section while avoiding crossing traffic. Shown

in table 4.4 below is a summary of the results obtained at site No. II.

Table 4.4: Summary of Survey Results

Mode To Changamwe Roundabout

From Changamwe Roundabout

Pedestrian 6542 6243

Handcart 116 104

Cyclist 867 924

Pedestrian traffic was majorly those to and from Changamwe shopping center as well as to the shops and

businesses along the road.


PLATE 1 to 4: The Transport Mess at Kwa Jomvu Junction

4.5 Origin – Destination (O/D) Studies 4.5.1 Introduction

Origin – Destination study was carried out by method of roadside interviews at Miritini with a view to

determining origins and destinations for passenger and commodity vehicles. The interviews were

done from 7.00 am to 6.00 pm during which efforts were made to facilitate personal interviews with

as many drivers as possible.

During the interviews, services of traffic police officers were used to help in stopping the vehicles

as the survey team interviewed the drivers in order to determine the following:

Trip origin for the trip being made

Trip destination for the trip being made

Commodity carried both by type and quantity

Vehicle occupancy

Purpose for which the trip was being made

Reasons for using the route of travel and possibility of using an alternative route


Classified manual counts were conducted simultaneously with the O/D surveys. O/D samples are

given for site No. 6 by various vehicle classes as shown below. The average sample size for all the

survey site was 37.47%. Table 4.5 gives the global format.

Table 4.5: Two – Day O/D Sample as per vehicle classification

Site O/D sample Vehicle Type TotalM/cy Car Light goods Buses Trucks Tractors

P/up,Van Matatu Light Medium HeavyVI Interviewed 95 423 483 743 417 257 522 2,224 6 5,170

Counted 796 2,158 2,483 2,699 590 437 1130 5,170 15 15,478% 11.9 19.6 19.5 27.5 70.7 58.8 46.2 43.0 40.0 37.47


It is important to note that fewer number motorcycles were interviewed because they made short trips

such as trips being made from one shopping centre to the next. The population was however high than

was interviewed. They formed a large population of passenger transport. Virtually, each motorcycle

had a passenger.

PLATE 5 and 6: Passenger Carrying Vehicles Being Interviewed

4.5.2 Traffic Zones

Traffic zones were established by the trip-end method and the resulting zones were divided as shown

below:

I. Local Zones

Zone Description

1 Mwembe Tayari, King’orani, Kilindini, Fort Jesus, Likoni Ferry (Island side),

Sabasaba, Ganjoni.


2 Voi, Mariakani, Port, Changamwe, Total, Shreeji, Jomvu, Migadini, Docks,

Mazeras, Tudor, Miritini, Mikindani, Chaani, Wundanyi, Refinery, Kobil

3 Kilifi, Nyali, Malindi, Bamburi, Mtwapa, Kaloleni, Kokoteni, Kiembeni, Mvita,

Kongowea

4 Ukunda, Likoni, Diani

II. External Zones

5 Dodoma, Tanga

6 Kapenguria, Kitale, Lodwar and Uganda (to include Tororo, Jinja), Nairobi, Thika,

Athi River, Limuru, Kiambu, Molo, Nakuru, Kericho,

4.5.3 Trip Matrices

Survey points for roadside interviews were 3 altogether and it was noticed that a vehicle interviewed at

site No.1 would possibly be interviewed again at another station; say station (5) and (12).

O/D sample was converted to Average Daily Traffic flows using the 24:12 hour ratio and ultimately

grossing it to Average Annual Daily Traffic flows. The grossing factors of the O/D sample are given in

table 4.6 for the particular vehicle categories.

Table 4.6: Conversion Factors for O/D Sample to AADT

Vehicle Type AADT factors

M/Cycle 1.82Car 1.54Pick-up 1.53Matatu 1.23Light Truck 1.76Medium Truck 1.77Heavy Truck 1.52Buses 2.05Tractors 1.25

Miritini is a crucial census point for the study in this road project. This is because it records nearly

90% of traffic out of Mombasa. The most attention in this study was given to traffic in the external

zones so as to be able to determine the possibility of easing the congestion on the road. The traffic

on this road segment appears to be regular and therefore a constant factor to be considered.


a) Motor cycle

Of the 95 motor cycle trips, 65 trips were made within zone 2 which includes Miritini, Kwa

Jomvu, Mikindani, Magongo (region to the West of Mombasa Island) and 16 trips came from

zone 1 and ended in zone 2. This is an indication that motorcycle trips were predominantly

localized for commuting within short distances or simply, on business trips.

b) Car

Car movement was very diverse due to the nature of dispersion of work places and homes. Of a

total 423 car trips, 99 ended in zone 2 from zone 2 while 50 trips ended in zone 2 from zone 1.

The zones can be referred to in the zoning table in the next section. The conclusion that can be

made from this observation is that most car trips are equally local. Quite a number of car trips

ended up in zone 6 which is the far west region of Nairobi, Thika, Western Kenya and the rest of

East Africa.

c) Pick-up/4WD/Vans

Of the 483 pick-up/4WD/Van vehicle trips interviewed, 292 of these trips were mainly in the local

zones 1, 2 and 3. Their travel demand was to supply retail goods and provide short distance travel

to individual owners who use them to transfer.

d) Matatu

Matatu vehicle trips were 743 in total of which 489 trips transported passengers between zones 1,

2 and 3 which are local zones. They transport people daily to town and back on various purposes.

The zones represent Mombasa Island, the region around Miritini and Northern Side of Mombasa.

e) Buses

Of the 417 bus trips, 126 trips involved large buses moving out of Mombasa to Zone 6 and back.

Small buses were mainly restricted to zone 1, 2 and 3 where they were mainly used by institutions

and tourists.

f) Medium trucks

A total of 522 medium truck trips were made, 324 trips were in the local zones 1, 2 and 3 with

another 84 trips ending in zone 6 mainly from zone 1 and 2. The Medium trucks transport goods

to regions around Mombasa with some of them finding their way to far west due to such demands.


g) Heavy trucks

Of the 2,224 heavy truck trips, 1537 trips were made to either end up in the external zones of 5

and 6 or to originate from there. This indicates that the travel need of Heavy truck vehicle is to

transport petroleum and industrial goods out of Mombasa. The remaining trips in the local zones

involved movement of empty containers to the depots in the region.

h) Tractors

Of the 6 tractor trips interviewed, all of the trips were within zone two since they mainly transport

empty containers between the depots. A summary of the AADT Origin- Destination survey data

by applying the 24:12 hr ratio is given in table 4.7 below.

Table 4.7: A Summary of AADT O/D survey Data

Global Trip Matrix

Origin Trip Destination Zone1 2 3 4 5 6

1 0 490 98 11 34 5812 562 1015 223 35 27 3733 146 198 65 12 9 784 16 20 15 0 1 135 24 42 37 0 0 06 224 596 117 94 9 2

Detailed Discussions

Site VI (Miritini)

The O/D survey was done on A109 road at Miritini so as to determine the amount of traffic through

Mombasa Island to the Southern mainland and far West regions of Nairobi and the rest of East and

Central Africa. The failure witnessed on the Road segment especially at Kwa Jomvu could

attributed to the low capacity of the road at that point since it is where the dual carriage way from

Mombasa ends. The O/D was also to establish the type of goods and tonnage that is handled by the

road. The O/D indicates that over 80% of the traffic movement on the road are within Mombasa or

coastal region.

The large number of passenger vehicles recorded at interview point was mainly on business.

However, the tourism and recreational activities for people on holiday since this was a holiday

season and Mombasa attracts a lot of activities and people.


There was a considerable high volume of heavy good vehicles interviewed. This is because of their

slow nature and their prevalence on the road. The presence is occasioned by the activities of the port

of Mombasa from where they transport the cargo cleared from the port. They mainly transport

industrial materials, construction materials and more significantly, petroleum products.

During the O/D, especially on the question of alternative route, it was realized that most motorists

(90%) were not aware of the alternative routes. The few who knew of the alternative routes

suggested that they could not use it because of poor conditions than the A109 road but would gladly

welcome an alternative to help them avoid the congestion.

Passenger Movement and Occupancy Ratings

Main passenger carriers namely Cars, Matatus, 4WD/Pickup/Van and Buses moved a total of 22,126

passengers. Cars moved a total of 933 passengers, Matatus moved 6397 passengers while Buses moved

7690 passengers. Vehicle occupancy rating per station is shown in table 4.8

Table 4.8: O/D Survey Occupancy Rating at Miritini

VehicleType

SITE 6: MIRITINI

Total Vehicles Total Passengers

Occupancy Rating Percentage Moved

Motorcycle 95 288 3 1.30Car 423 933 2 4.224WD/P-up,Van 483 924 2 4.18Matatu 743 6397 9 28.91Bus 417 13584 33 61.39Total 2,161 22,126 9 100%


4.5.4 Trip Purpose

Table 4.9: Global Trip Purpose

Business Work Social Education Medical Home Total Motorcycle 69 9 3 0 3 11 95Car 67 123 103 2 9 119 423Pick up/ van 198 107 64 1 8 104 483Matatu 459 134 53 16 13 58 743Buses 282 60 54 15 0 6 417Light truck 149 104 7 - - 7 257Medium truck

265 232 - - - 25 522

Heavy truck 1303 919 - - - 2 2224Tractors 5 1 - - - 6Total 2797 1689 284 34 33 332 5,170Percentage 54.10% 32.70% 5.40% 0.70% 0.60% 6.40% 100%

Summary of Trip Purpose

Table 4.9 gives the global view of the vehicular trips interviewed in the whole study by purpose.

The trip distributions by motorized traffic by purpose were as follows:

Business = 54.1%

Work = 32.7%

Social = 5.4%

Educational = 0.7%

Medical = 0.6%

Home = 6.4%


54.10%32.70%

5.40%

0.70%

0.60% 6.40%

BusinessWorkSocialEducationalMedical Home

Fig 4.2 Pie Chart Showing Trip purpose

Discussions on Trip Purpose

Business

Business trips were practically market oriented and were made in Motorcycles, Light goods

vehicles, Medium goods vehicles, Heavy goods vehicles and Buses. Matatus ferrying passengers

from one point to their destinations is also considered as business trips.

Work

These were trips made by people on employment i.e. lecturers from Nairobi University and

Kenyatta University, Government Officials, bankers’ etc. This trip purpose was predominant by

those using private vehicles notably cars.

Medical

These trips were mainly those made to district hospitals and other medical dispensaries by those

seeking medical attention or visiting patients.

Social

These were trips made to funerals, visiting friends, shopping, religious reasons and leisure. The

main component of vehicles under this category was tourist vans and school buses on holiday at

the coast during the December festive season.

Educational

There were very few school trips made due to the fact that this was a festive season and schools

were closed. The few that were captured were on educational trips which involved visiting the


historical sites, national parks and the coastal recreational facilities. The study having taken place

during the holiday season when most schools were closed for holidays, few trips were registered

to be going for educational trips save for the school tours.

Home

These trips were mainly made during evening hours by people going back home from work and

those made during the day by those coming from long distances to visit their homes. Other trips

made during day to homes were of those people who had come to make purchases of goods for

varies convenient purposes in town and back home.

4.6 Traffic Forecast 4.6.1 Generated Traffic

This is the additional travel that results from transportation improvement. Traffic Volume increases until

saturation or congestion develops when equilibrium is achieved.

In a paper published in the Institute of Traffic Engineer Journal (ITE) April 2001, generated traffic is

defined as to consist of:

a) Trips diverted from other routes.

This would be the traffic moving from other alternative routes onto the project route. In the case

of A109 and A109A roads, it appears there would not be much or any of this kind of traffic since

there is currently no viable route. The otherwise considered as possible routes are still under

feasibility studies or have since been neglected to the point that no motorised traffic uses them.

b) Trips diverted from other modes

From the traffic count on the various road segments, it has been established that the traffic

composition is fairly representative with all vehicle classes present in good numbers. The vehicles

that use the road are obligated to use it since their travel demands are only met when they use the

road. Therefore, there are minimal or no chances of other modes of travel being diverted into the

project road upon completion. The only increase however, could be increased frequency of people

using the road due to the improvements.

Thus over the long period generated traffic consists of induced travels that increased additional

vehicle mileage.


In recent years an accumulating body of theoretical and empirical evidence based on various

analytical techniques has been used to measure generated traffic. Findings from some major

studies indicate the following:

Time series travel data for various types of roadways, indicate that half of increased roadway

capacity is consumed by additional trend that would not otherwise occur within five years,

80% eventually be consumed by this induced vehicle travel.

A study by leading U.K transportation economists conclude that reducing travel time on a

roadway by 20% typically increases traffic flow by 10% in the short run and 20% in the long

run.

4.6.2 Normal Growth

The following percentage growth rates were adopted for the design.

Cars - 4 Per cent

Light Goods - 5 Per cent

Medium Goods - 4 Per cent

Heavy Goods - 6 Per cent

Buses - 4 Per cent

Motorcycle - 7 Per cent

Tractor - 3 Per cent

The number of motor cycle traffic is expected to drop once the road is improved to bitumen

standards as this will present cheaper, faster and even safer modes of transport in form of Matatus

and cars on the project road. The growth on Matatu however has been considered due to expected

increase on people moving from traditional use of bicycles for short distances. Moreover, the delay

caused by Matatus while trying to get passengers can be avoided by people who use motorcycles

since it requires only one passenger.

Traffic forecasts on the design road are based on three parameters;

Normal growth: which is growth rate so far on the road project to apply over the period of

design.

Immediate growth: This is growth following the improvement of the road facility. A ten-

year period has been seen to be practical.

Long-term growth: This is for a period of ten years after the immediate growth.


The growth in motor cycles will be low as the road condition is improved and attracts other passenger

carriers. The vehicle classification by the Ministry is limited to those presented in table 4.10 below

and the growths are combined for the vehicle types so as to conform to the Ministry of Roads

classification for forecasting. Three growth rates have been used for the sensitivity analysis.

Table 4.10: A Summary of Adopted Growth Factors for Traffic Forecasting

Percent growth by vehicle type (%)

Car L.G M.G H.G Bus M/CyTract

or

2012-2014 (3 yrs) normal growth 4 5 4 6 4 7 3

(10 yrs) 2024 Immediate impact (%)Low 5 6 5 7 5 8 4

Medium 6 7 6 8 6 9 5High 7 8 7 9 7 10 6

(10 yrs) 2034 Long-term impact (%)Low 3 4 3 4 3 3 3

Medium 4 5 4 6 4 5 4High 5 6 5 7 5 7 5

NB:Future traffic is tabulated in appendix 1A-1C


Chapter 5

5. DESIGN CALCULATIONS 5.1 The straight

The terrain renders the road suitable for a design speed of 80 km/hr along the alignment except for

interchange sections which qualifies for design speed of 30Kph because of the radii of the bends and the

train tracks traversing the road at Kona reli, therefore the speed is reduced to allow for a bridge crossing.

All town centres will however be restricted to 50Km/hr by use of speed limit signs located before and

after the townships. This makes the road an urban type II with reference to chapter 2. Table 5.1 below

summarises design speeds adopted for geometric design of the project road.

As mentioned in chapter 2:

Length ≤ 20VD

Table 5.1: Different design speeds and their maximum lengths

SECTION DESIGN SPEED,VD MAXIMUM LENGTH

2- Changamwe interchange( junction of A109 and A109A towards Mombasa )

30 600

4- Airport Roundabout to Changamwe(lies along A109A en route to airport)

50 1000

6- Refinery Roundabout to Airport Roundabout

(lies along A109A en route to refinery)

50 1000

8- Kona Relly interchange(lies at the junction heading to Miritini and Magongo estates)

30 600

10- Kwa Jomvu interchange( junction of A109 and A109A towards Nairobi)

30 600

Straights between circular curves following the same direction should not have lengths less than 200m to allow super elevation run-off.

Accordingly, cross-section design parameters have been extrapolated and given in table 5.2 below.


Table 5.2: Passenger car units

Vehicle type

P.C.U Factor

Seg. I Seg. II Seg. IIIAADT(10 yr)

P.C.U AADT(10 yr)

P.C.U AADT(10yr)

P.C.U

M/Cy 0.5 12078 6039 4965 2483 4589 2294Cars 1 15089 15089 4132 4132 3043 3043LGO 1.5 11054 16581 2594 3891 3223 4834LGM 1.5 15431 23146 3587 5380 4344 6516L. Truck 5 1714 8570 635 3175 1092 5460M. Truck 5 3711 18555 908 4540 2555 12775H. Rigid 8 2389 19112 825 6600 1235 9880H. Articu 8 5315 42520 3345 26760 5380 43040Bus 4 3919 15676 287 1148 1232 4928Tractor 8 836 6688 292 2336 88 704Total 171976 60445 93474 11%pcu

18917

6,649

10282

For design purposes, PCUs are taken on the hour basis and is referred to as Design Hour Volume (DHV). However, peak hour volumes are always avoided as they rarely occur during the determination of AADT. This is always the case so as to avoid overdesigning the facility.In the event the hourly traffic cannot be obtained, as is the case, the studies have established that, the

DHV is always between 10-11.5% of AADT. In our case, due to the urban influence on the project road,

we have taken the 11%.

According to the HCM (Highway Capacity Manual) criteria for section capacity the following

assumptions are considered:


TABLE 5.3: EXAMPLE SERVICE VOLUMES FOR MULTILANE

HIGHWAYS

(SEE FOOTNOTE FOR ASSUMED VALUES)

FFS

(km/h)

Number of Lanes Terrain Service Volumes (veh/h)

A B C D E

100 2 Level 1200 188

0

2700 3450 4060

Rolling 1140 180

0

2570 3290 3870

Mountainous 1040 164

0

2350 3010 3540

3 Level 1800 283

0

4050 5180

Rolling 1710 270

0

3860 4940 5810


0

3530 4520 5320

80 2 Level 960 151

0

2190 2920 3520

Rolling 910 144

0

2090 2790 3360

Mountainous 830 131

0

1910 2550 3070

3 Level 1440 226

0

3290 4390 5290


Rolling 1370 216

0

3140 4180 5040


0

2870 3830 4610

Notes:

Assumptions: highway with 100 km/h FFS has 5 access points/km; highway with 80 km/h

FFS has 15 access points/km; lane width 3.6 m; shoulder width 1.8 m; divided highway; PHF

0.88; 5 percent trucks; and regular commuters.

Based on the above, the following Chainages represent location of Access Culverts on the road:

TABLE 5.4 ACCESS CULVERT LOCATIONS

(A) CHANGAMWE-MAGONGO( A109A)Item Chainage Item Chainage

1 0+050 RHS 11 1+870 LHS

2 0+250 RHS 12 2+010 LHS & RHS

3 0+750 LHS 13 2+070 RHS4 0+990 LHS 14 2+220 RHS5 1+160 RHS 15 2+340 RHS6 1+260 LHS 16 2+480 RHS7 1+650 LHS 17 2+550 RHS8 1+770 RHS 18 2+580 LHS9 1+800 LHS 19 2+600RHS10 1+830 RHS 20 3+650 RHS


The Access culverts will also be of similar construction. The locations have been decided by examining

the existing drainage structures and the proposed alignment profile. The pre-cast concrete pipes proposed

will have complete concrete surround. The amount of fill allowed for is a minimum of 0.6m above the

culvert surround. The inlet and outlet structures will comprise reinforced concrete headwalls. A summary

of the culverts is as per table 6.1. Table 5.5 below shows the Ministry of Roads cross section design

guideline based on pcus.

Table 5.5: Geometric Cross section Types by pcu

AADT or DHV in Year 10Cross section Type

(pcu)

AADT< 150 V,VI,VII,VIII (I)

150<AADT<500 IV,V,VII (II)

500< AADT < 2000 III,VI (III)

2000 < AADT < 4000

II,III (III)Or

250< DHV < 500

4000 < AADT < 8000

IIOr

DHV>500

AADT>8000 Not specified (Dual)

Source RDM, Part 1

Based on the above pcus, segment I and III will be dual carriageway since they have pcus > 8,000

as recommended in the Road design manual, with the cross section being type I.

5.2 Vertical Alignment Design

The main design criterion for vertical curves is ensuring the fulfilment of the requirement for the minimum stopping sight distance as stipulated in the Road Design Manual Part 1. The other design considerations include drainage, aesthetics and comfort for vehicle occupants.

The new vertical alignment was designed to follow the existing terrain as closely as possible to minimize earthworks. However, minimal cut and fill were allowed where necessary.


A summary of the vertical alignment standards adopted for the project road is presented in the Table 5.4 below:

Table 5.4: Vertical Alignment Standards

Design Elements Design Speed

50Kph 60Kph 80KphMax. gradients, flat terrain

Max. gradients, rolling terrain

Max. gradient, mountainous terrain

Min. gradients (in cuts)

Minimum stopping sight distance

Min. crests curve radii (stopping sight dist.)

Min. crests curve radii (passing sight dist.)

Min. sag curve radii (stopping sight dist.)

-

7.0%

9.0%

0.5%

65 m

430 m

900 m

1,200 m

-

6.0%

8.0%

0.5%

85m

800m

1,750m

1800m

4%

5%

-

0.5%

130 m

1,750 m

3,750 m

3,000 m

Source RDM, Part 1

The vertical curves were checked for compliance to the design criteria as stipulated in the Road Design Manual Part I. The curves were found to meet the requirements for minimum stopping sight distances.

5.3 The Road Reserve

The road reserve is 40m throughout the project road. Land shall be acquired where realignments have affected the road reserve.

5.4 Drainage There are no streams crossings along the project road. The side ditches are designed to carry storm water

run-off originating from the carriageway and any run off from beyond the road width. As a normal

standard requirement a cross culvert has been allowed for at the locations where there are existing

culverts and every 250m along the road as necessary and are designed to carry storm from side ditches to

the outfall drains. Additional culverts will be provided during construction if necessity arises. The

formation of contours established during survey Drainage capacity analysis gives a general indication of

possible locations of cross culverts.

The capacities of drainage structures have been calculated using the following formulae that assume full flow in the respective structures:

For pipe culverts:


Q = 2.8 rH3/2

Where:

Q = discharge in m³/s;

r = the radius of the pipe in metres;

H = depth of water upstream.

For box culverts and bridges:

Q = 1.7LH3/2

Where:

Q = discharge in m³/s;

L = width in metres;

H = depth of water upstream.

For side ditches:

The side ditches are designed to carry the storm water run-off originating from the carriageway drain and cut slope. The expected flow, or run-off has been estimated using the rational formula;

Q=0.278C.I.A

Where;-

Q is the expected flow (m3/s)

C is the run-off coefficient (suggested value 0.9 for pavement, drain and cut slope)

I is the intensity of rainfall (mm/h) for a 10 minute storm with a return period of 5year

A is the area drained (km2)

The capacity of side ditch has been estimated using the Manning-Strikler formula i.e.

Q=KAR2/3S1/2=A.V

Or V=KR2/3S1/2

Where:-

Q is the capacity (m3/s)

A is the cross-sectional area of water (m2)

V is the velocity of flow (m/s)

R is the hydraulic radius, A/P where P is the wetted perimeter

K is the roughness coefficient

S is the longitudinal slope (m/m)

5.4.1 Sizing of Culverts and Side Ditches

The typical result of the calculated hydraulic capacity using the formulae above is included in appendix 3A of the report


.

Chapter 6

6. RECOMMENDED DESIGN PARAMETERS 6.1 Geometric design 6.1.1 Cross-Section

Appropriate cross-section for the project road was chosen based on road function, projected traffic

volume and design speed. Cross-section type I (7m dual carriageway) is recommended. Width varies

along the road (reducing to a 7m single carriageway) with slip roads and Interchanges of 4m lanes one

way direction.

6.1.2 Horizontal Alignment


The design speed has been taken as 50 km/h for the entire length of the project road. The interchanges

have a design speed of 30 km/h. Desirable road reserve was taken as 40m.

The areas whose horizontal alignment standards did not meet the minimum design requirements as

stipulated in the RDM Part 1 were realigned mainly to achieve the required clearances and to provide

adequate sight distances. Land acquisition must also be carried out in these areas.

6.1.3 Vertical Alignment

The main design criterion for vertical curves is ensuring the fulfilment of the requirement for minimum

stopping sight distance as stipulated in the Road Design Manual Part 1. The other design considerations

include drainage, aesthetics and comfort for vehicle occupants.

The new vertical alignment followed the existing terrain, except where ground conditions dictated

otherwise. In some sections, it was necessary to design for cuttings to improve road safety, improve road

drainage and achieve adequate clearances. The cut material will be used as fill in areas where the

proposed finished road level is higher than the existing ground level.

6.2 NMT Facilities Since Pedestrians and Cyclists traffic was majorly those to and from Changamwe shopping center as well

as to the shops and businesses along the road, an overpass must be provided between the Changamwe

interchange and the Airport Roundabout. This increases mobility and safety of the Pedestrians and the

cyclists as they move across or along the road. A representation of an overpass is shown below:

Fig. 6.1 Example of An overpass.


6.3 Bus Bays Bus bays of 40 m width should be provided near the Airport Junction and Refinery Junction on both

sides. They should be tapered gradually towards the carriageway at each end so that buses can leave or

rejoin the traffic stream smoothly and safely. They should be staggered tail-to-tail at between 500 – 800

m apart.

6.4 Detailed Structural Design 6.4.1 Sizing of Drainage Structures

The size of drainage structures has been determined using design flood calculations as carried out. Pipe

culverts of opening less than 5m2 to pass 5year flood.

Velocity of stream flow estimated using Manning’s formula.

Area obtained checked using inlet control table for culverts.

The drainage structures mainly consist of pipe culverts, mitre drains, scour checks, and catch water drains and outfall drains. The proposed new structures are presented in Table 6.1 below.

Table 6.10: Proposed structures

Item Chainage Existing Structure Proposed Drainage Structure

(A) CHANGAMWE-KWA JOMVU( A109A)

1 4+500 4x 900 PC Retain existing culverts

2 4+400 1 x 900 PC Retain existing culvert

3 4+200 1x 900 PC Retain Existing culvert





8 0+560 2 x 600 PC Replace with 2x900PCC

9 0+000 - 0+750 LHS 1200 PC New underground drainage system

10 0+050 - 0+4800 LHS 1200 PC New underground drainage system

11 4+700 - 4+900 RHS & LHS 1200 PC New underground drainage system

12 5+000 - 5+100 RHS & LHS 1200 PC New underground drainage system

(B) CHANGAMWE-MIRITINI( A109) - AT KWA JOMVU INTERCHANGE


1 0+450 - 0+665 1200 PC New underground drainage system

2 0+560 - 0+900 1200 PC New underground drainage system

6.4.2 Bridges

There are several bridges designed on both roads A109 and A109A mostly due to the interchanges at

grade separations and crossings at the railway line. These include:

a) Changamwe Interchange Bridge along A109

b) 2 Bridges along A109A

c) Kwa Jomvu Interchange Bridges;

One across A109

One across A109A

2 Railway bridges

The proposed new bridges are reinforced concrete structures supported at abutment and piers. The overall

clearance is 5.5m whereas for bridges over the railway have a clearance of 7.2.

The global geometry of the bridges is dictated by the following parameters:

Nature of the grade separation at the interchanges

Approach road profile at the bridge location

Vertical profile of the approach road

The bridges are provided with longitudinal gradient, which matches the approach road levels on either

side of the bridge. Cross drainage is proposed with a transverse gradient to ensure rapid drainage of the

deck. Galvanised deck drains have been provided at 3m interval and will discharge the water on the deck

to the side drains depending on the nature of the interchange. Edge drips have been provided on either

side of the cantilevered portion of the deck to ensure the water on the face of the kerbs drips without

staining the beams.

The global geometry of the pipe culverts is dictated by the following parameters:

Channel top level estimated based on hydrological flood calculations.

Channel profile at the pipe culvert location.

Vertical profile of the approach road.


Chapter 7

7. CONCLUSION AND RECOMMENDATIONS This chapter gives possible recommendations of measures which can be applied to the designed road

to ensure maximum safety and efficiency.

7.1 Installation of Bollards It is proposed that bollards be provided on the edges of the entire length of the road for the safety

of the pedestrians. It would be ideal to do this on the entire road provided there is adequate

funding. An alternative would be to install triangular blocks of stone which have been dug into the

ground.


7.2 Introduction of speed humps Speed bumps should also be provided in various sections of the road so as to eliminate excessive

speeds where through traffic would represent accident risks. The dimensions of the speed bumps

should be as follows:

Height – 5 to 8 cm. Length – 1.5 to 5m for slowing down and 1.5 to 2.5m for complete stopping. Radius - 100-200mm. Intervals – 50 to 70m in busy areas

Road signs should be erected to warn motorists of bump ahead and the bumps should be painted white and if possible the paint should be reflective.

7.3 Traffic Signs and Road Marking Erection of traffic signs will contribute to improvement of safety of the pedestrians crossing the

road. Stop and Give Way signs can be placed at the minor roads to indicate to drivers that the

motorists on the major road have priority. These two signs are regulatory signs and they appear as

follows;

Fig 8.2: Examples of traffic signs

Some signs such as those warning drivers who are especially new in the area of presence of children crossing should be put up. This would ensure improved safety for children crossing the road. These signs should be put up at all the approaches as children may be crossing from any point other than those provided. Other Road Signs include:


Figure 8.3 Example of Various Road signs in Kenya

Provision for centerline and edge markings should be made for the entire road network. The pavement surface should also be marked to demarcate traffic lanes, to guide vehicles at intersections and to show the position of bus stops.

7.4 Street Lighting Street lamps should be installed for the amenity and safety of road users and residents. Since the road

activity in the area is minimal at night, it will be economical to make use of incandescent lamps to

improve visibility.

References 1. DESIGN MANUAL for ROADS and BRIDGES, AASHTO. (2001)

2. Two-Lane Rural Highway Safety Public Roads,Vol.48 (pp. 48-53) by Brinkman, (1984).

3. Traffic planning and Engineering by Hobbs (1979)

4. Curvilinear Alignment: An Important Issue for a More Consistent and Safer Road Characteristic pp. (12-21), by Lamm, R. a. (1994)

5. DESIGN MANUAL FOR ROADS & BRIDGES by MINISTRY OF ROADS Nairobi (2009 (Draft Manual)).

6. Highway Engineering by Rogers, M. (2003). Blackwell Publishing Ltd.


7. Roads in Urban Areas in Scotland, (1973).

8. Traffic engineering design by Slinn, M, Guest, P, & Mathews.

9. Traffic and Highway Engineering (Fourth Edition) by Hoel, N. J. (2009).

10. Kenya Road Board Web site: (http://www.krb.go.ke/classification), (2014, November 24)

11. Ministry of Roads Traffic Census Points, from Ministry of Roads (1988-2001).

12. INTRODUCTION TO GEOMETRIC DESIGN by Rao, T. V. (2006) from India.

13. TRAFFIC SURVEY REPORT FOR PRELIMINARY AND DETAILED ENGINEERING DESIGN FOR CHANGAMWE-MAGONGO-MIRITINI from SAMU Engineering Consultants Ltd. (2012), Nairobi.

14. Geometric Design Guideline by the South African National Road Agency in Cape Town. (2000)

15. TRRL Laboratory Report by UK: Transport and Road Research Laboratory, Department of Environment. (1976)


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