transport engineering 333

7/27/2019 Transport Engineering 333

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FCE 346 - TRANSPORTATION ENGINEERING I (45 HRS).

a) Principles and objectives of transportation.

b) Modes of transportation.

c) Role of transportation in society, economic, social, political and environmental.

d) Introduction to traffic Engineering.

e) Traffic regulations.

f) Traffic survey procedures and data collection.

g) Traffic volume, speed and concentration.

h) Vehicles, driver and pedestrian characteristics.

i) Road safety. Road user psychological traits.

j) Highway capacity and level of service.

k) Introduction to urban and regional planning.

Practical works - Traffic volume and speed surveys.

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REPORT TITLE CONTENTS

Chapter Description Page

1 THE TRANSPORTATION SYSTEM 8

1.1 Definition and Scope 8

1.1.1 Fixed Facilities 8

1.1.2 Flow Entities and Technology 8

1.1.3 Control System 8

1.1.4 Transportation Demand 9

1.2 Transportation System Classification 9

1.2.1 Classification Schemes 9


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1.2.2 Major Transportation Subsystems 9

1.2.3 Private and Public Transportation 10

1.2.4 Urban Transportation Systems 10

1.3 The Nature of Transportation Engineering 11

1.4 The Systems Approach in Transportation Engineering 12

1.5 Transportation Policymaking 13

1.6 Movement and Transportation 14

2 CHARACTERISTICS OF TRANSPORTATION SYSTEMS 16

2.1 Elements of Transportation Systems 16

2.2 The Role of Government 19

2.2.1 Governmental Participation 19

2.2.2 Instruments of Governmental Involvement 19

2.3 Tools and Applications 20

2.4 The Role of Transport in Society 20

2.5 Introducing Comprehensive Transport Planning 21

2.5.1 Redefining the Objective 21

2.5.2 The 'Carrot' and the 'Stick' 21

2.5.3 Comprehensive Planning 22

2.5.4 The Transportation Study 23

2.6 Transportation Systems, Hierarchies, and Classification 24

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2.6.1 Traffic Classification Systems 24

2.6.2 Road Classification Systems 26

(a) Rural road systems 26

(b) Urban road systems 29


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3 TRAFFIC ENGINEERING 33

3.1 Definition 33

3.2 Growth of the Subject of Traffic Engineering 33

3.3 Functions Traffic Engineer 33

4 SPEED, JOURNEY TIME AND DELAY SURVEYS 35

4.1 Definitions 35

4.2 Use of Speed, Journey Time and Delay Studies 35

4.2.1 Methods of Measuring Spot Speeds 36

4.2.2 Direct-Timing Procedure for Spot Speed Determination 36

4.2.3 Radar Speed Meters 36

4.2.4 Photographic Method and Video Camera Method 36

4.2.5 Methods for Measurement of Running Speed and Journey Speed37

(a) Moving Observer Method 37

(b) Registration Number Method 37

(c) Elevated Observer Method 37

5 VEHICLE VOLUME COUNTS, CLASSIFICATION AND OCCUPANCY 38

5.1 Need for Vehicle Volume, Classification and Occupation Counts38

5.2 Vehicle Classification Error! Bookmark not defined.

5.3 Types of Counts 38

5.3.1 Short term and long term counts 39

5.3.2 Method Available for Traffic Counts 39

5.3.3 Vehicle Occupancy Surveys 40

5.4 Origin-Destination Survey 40

5.4.1 Survey Methods 41

5.4.2 Checking the Accuracy of O-D Survey Data 41


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5.4.3 Presentation of Results 41

6 TRAFFIC REGULATION 43

6.1 Basic Principles of Regulation 43

6.1.1 Need for regulation of traffic 43

6.1.2 Scope of traffic regulations 43

6.1.3 Traffic laws 43

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6.2 Regulation of Speed 44

6.2.1 Need for regulation of speed 44

6.2.2 General principles governing application of speed limits 44

6.2.3 Speed limits in urban areas 45

6.2.4 Speed limits in rural areas 46

6.2.5 Problem of Small Villages along Rural Highways 46

6.2.6 Speed limits for different types of vehicles 46

6.2.7 Speed limits at nights 47

6.2.8 Criteria for application of speed limits of 50, 65, 80 and 100 kph 47

6.2.9 Enforcement methods and instruments for detection of speed violators 50

6.2.10 Speed zoning 50

(a) Speed zoning at horizontal curves 50

(b) 17-2-10-3. Safe speeds at intersections 51

6.2.11 Speed laws 54

6.2.12 General effect of speed limits 54

6.3 Regulation of Vehicles 55

6.3.1 Vehicle Registration 55

6.3.2 Construction and equipment of vehicles 55


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6.3.3 Control of Transport Vehicles 56

6.3.4 Insurance 56

6.4 Regulations Concerning the Driver 56

6.4.1 Licensing of the Driver 56

6.4.2 Physical Fitness 56

6.4.3 Age of Drivers 57

6.4.4 Disqualification and endorsement of Licence 57

6.4.5 Offences and Penalties 57

6.5 Regulations Concerning Traffic 57

6.5.1 Cycles 57

6.5.2 Motor Cycles and Scooters 58

6.5.3 Rules for Pedestrian Traffic 58

6.5.4 Rules for animal vehicles 58

6.5.5 Rules for animal on streets 58

6.6 General Rules Concerning Traffic 59

6.6.1 "Keep to the left" rule 59

6.6.2 Overtaking rules 59

6.6.3 Turning rules 59

6.6.4 Priority rules at intersection 60

6.6.5 Hand signals 60

6.6.6 Rules intended to promote pedestrian movement on footways 60

6.7 Parking Regulations 61

6.7.1 Need for parking regulations 61

6.7.2 Types of regulations that are normally imposed. 61

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6.7.3 Restrictions on loading and unloading of commercial vehicles. 61

6.7.4 Exclusive parking spaces for taxis 61

6.7.5 Reservation of curb space for bus stops 61

6.7.6 Restrictions on parking near intersections 61

6.7.7 Limitations on curb parkingdesignation of parking places along the curb 62

6.7.8 Peak hour parking prohibitions 62

6.7.9 Parking control by fees 62

6.8 Enforcement of Regulations 62

6.8.1 Importance of enforcement and punishment 62

6.8.2 Goals and objectives 62

6.8.3 Machinery for enforcement 62

6.8.4 The police 63

6.8.5 The courts 63

7 ROAD USER AND VEHICLE CHARACTERISTICS 65

7.1 Human Factors Governing Road User Behaviour 65

7.1.1 Human body as a complex system 65

7.1.2 Vision 65

7.1.3 Hearing 65

7.1.4 Perception, intellection, emotion and volition 65

7.2 Pedestrian Characteristics 66

7.3 Vehicle Characteristics 66

8 ROAD SAFETY 67

8.1 Introduction 67

8.2 Elements of Road Safety 67

8.3 A Simplified Framework 69


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8.4 Collection of Accident Data 72

8.4.1 Introduction 72

8.4.2 Requirements of accident records 72

8.4.3 Standard definitions 72

8.4.4 Standard accidents reporting forms 73

8.4.5 Collision diagrams and collision diagram 73

8.5 Statistical Methods for Analysis of Accident Data 74

8.6 Road and its Effect on Accidents 74

8.7 The Vehicle 76

i. fewer in number, 76

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ii. less serious to other road user 76

iii. less severe to vehicle occupants 76

8.7.1 Braking system 76

8.7.2 Vehicle lighting system 76

8.7.3 Vehicle body-its features 76

i. the shape and dimensions of the driver's seat 76

ii. arrangement of dials on the dash board 77

iii. positioning of controls in relation to the driver's seat 77

iv. visibility of the driver from the seat 77

v. noise levels in the vehicle 77

vi. concentration of carbon monoxide inside the vehicle. 77

8.7.4 Tyres 77

8.7.5 Vehicle inspection and maintenance 77

8.8 The Driver 77


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8.8.1 Drivel-judgment, skill and emotional make-up 77

8.8.2 Age of drivers 78

8.8.3 Sex of the drivers 78

8.8.4 Martial status 78

8.8.5 Training of drivers 78

8.8.6 Alcohol and drugs and the driver 79

8.8.7 Fatigue 79

8.8.8 Use of crash helmets 79

8.8.9 Use of safety belts 80

8.9 Skidding 80

8.10 Speed in Relation to Safety 80

i. The distance needed to bring a vehicle to a stop increases as the speed increases. 80

8.11 Weather and its Effect on Accidents 81

8.12 Pedestrian Safety 81

8.12.1 Seriousness of the pedestrian safety problem 81

8.12.2 Trends in pedestrian accident pattern 81

8.12.3 The road and its influence on the pedestrian accidents 82

8.12.4 Pedestrian footways 83

8.12.5 Time and its influence on pedestrian accidents 83

i. Dark period of heavy traffic usually cause frequent pedestrian accidents. This normally corresponds to

the evening rush hour traffic in winter. 83

ii. Pedestrian accident rates are high during weekdays when the traffic flow is heavy. 83

iii. Special rush days such as Christmas have large number of accidents. 83

8.13 Cyclists 84

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8.14 Motorcycle and Scooter Riders 85


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8.15 Parking and its Influence on Accidents 86

8.16 Traffic Management Measures and Their Influence in Accident Prevention 86

8.17 Legislation, Enforcement, Education and Propaganda 86

8.17.1 Legislative measures that are possible 86

8.17.2 Enforcement 87

8.17.3 Education 87

8.17.4 Propaganda 88

8.18 Cost of Road Accidents 88

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1 THE TRANSPORTATION SYSTEM

1.1 Definition and Scope

A transportation system consists of fixed facilities, flow entities, and the control system that permit

people and goods to overcome the friction of geographical space efficiently in order to participate in a

timely manner in some desired activity. This definition helps to focus on the breadth of transportation

engineering and to delineate the purpose and scope of this introductory text. It identifies the functional

components of a transportation system (the fixed facilities, the flow entities, and the control system)

and encapsulates the fact that transportation provides the connectivity that facilitates other societal

interactions.

1.1.1 Fixed Facilities

Fixed facilities are the physical components of the system that are fixed in space and constitute the

network of Links (e.g., roadway segments, railway track, pipes) and nodes (e.g., intersections,

interchanges, transit terminals, harbours, and airports) of the transportation system. Their design, which

has traditionally been within the realm of civil engineering, includes soil and foundation engineering,

structural design, the design of drainage systems, and geometric design, which is concerned with the

physical proportioning of the elements of fixed facilities. Although related, geometric design is different

from other aspects of design (e.g., structural design, which is concerned with the strength of structures

to withstand efficiently the expected forces or loads).

1.1.2 Flow Entities and Technology

Flow entities are the units that traverse the fixed facilities. They include vehicles, container units,

railroad cars, etc. In the case of the highway system, the fixed facilities are expected to accommodate a

wide variety of vehicle types ranging from bicycles to large tractor-trailer combinations.


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1.1.3 Control System

The control system consists of vehicular control and flow control.

Vehicular control refers to the technological way in which individual vehicles are guided on the fixed

facilities. Such control can be manual or automated. Proper geometric design of the fixed facilities must

incorporate characteristics of the vehicle and vehicular control system. These include driver

characteristics (e.g. time a driver takes to perceive and react to various stimuli) for highway facilities

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where the "vehicles are manually controlled. Similar but more precisely definable response times exist

in the case of automated systems. The flow control system consists of the means that permit the

efficient and smooth operation of streams of vehicles and the reduction of conflicts between vehicles.

This system includes various types of signing, marking, and signal systems and the concomitant rules of

operation.

1.1.4 Transportation Demand

Transportation systems are constructed to serve people in undertaking their economic, social, and

cultural activities. Transportation demand is derived, or indirect, meaning that people normally travel in

order to accomplish something else, for example, to go to school, to work, to shop, or to visit with

friends. By the same token, workers get into the morning and evening rush hours because their work

schedules require it. Transportation engineers are concerned with accommodating these societal

activities by providing efficient ways to satisfy the population's needs for mobility. The word efficient

stands for the balancing a variety of often conflicting requirements, including cost considerations,

convenience, protection of environmental quality, and protection of individual rights. Transportation

engineers often cooperate with other professionals, including economists, planners, and social

scientists.

1.2 Transportation System Classification

1.2.1 Classification Schemes

Transportation .systems can be categorized in several ways. E.g. according to technology, function or

type of service, ownership or responsibility for implementation and operation, etc.

1.2.2 Major Transportation Subsystems

The transportation system is further categorized into four major subsystems according to the medium

on which the flow elements are supported commonly referred to as modes. The term mode is also used

to make finer distinctions between the various means of travel, e.g. driving alone and forming car pools

are sometimes considered to be different modes. The four major subsystems are 1. Land transportation:

a. Highway; b. Rail

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2. Air transportation: a. Domestic; b. International 3. Water transportation: a. inland; b. Coastal; c.

Ocean 4. Pipelines: a. Oil; b. Gas; c. Other Pipelines differ from the other three subsystems in that they

are suited only for freight transportation and they do not employ vehicles. The water transportation

subsystem consists of inland, coastal, and ocean transportation. The air transportation system uses

aircraft that are supported by stationary or rotary air foils. This subsystem may be conveniently divided

into domestic and international services. It is predominantly used for passenger transportation and

carries only a miniscule amount of freight, usually confined to specialized items such as mail and

valuable commodities. The land transportation subsystem is further subdivided into its highway and

railway components because of their fundamental technological differences and their networks are

spatially separated.

1.2.3 Private and Public Transportation

Transportation services are also classified as either/or hire (public) or not-for-hire (private) services.

These terms refer to their availability to the general public and to private parties, and not to their

ownership. E.g. a city bus system may be owned either privately or publicly. In either case, the service

provided is public transportation because the system is available for use by the general public. For-hire

systems are further classified into contract carriers and common carriers. Contract carriers stand ready

to provide service to the public under individual contractual arrangements. Common carriers, on the

other hand, generally offer scheduled service and are open to all members of the public willing to pay

the posted fare. The terms mass transportation or mass transit usually refer to the common carriage of

passengers. Taxis, car rentals, and certain other individually arranged services belong to the category of

contract public transportation.

1.2.4 Urban Transportation Systems

The intercity or urban distribution of freight is predominantly accomplished by the highway subsystemusing vans and trucks of various sizes. The major movements within urban areas are related to the travel

undertaken by people. Water-based urban transportation is found in only a few cities, and air

transportation is unsuited for urban travel.

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Thus the means of travel available for urban passenger transportation are in the main land-based and

include private transportation (walking and private motor vehicles) and various public transportation

services, of which some are highway-based (i.e., regular city buses), others are not (e.g., urban rail

transit systems). Rapid transit refers to all exclusive right-of-way systems. To clarify other technological

differences, modifiers such as heavy rail, light rail, fixed guide way, further discussion of specific

technologies that belong to these overlapping categories may be found in the technical literature.

1.3 The Nature of Transportation Engineering

Transportation engineering is a multidisciplinary area of study. The profession carries a distinct societal

responsibility. Concepts drawn from the fields of economics, geography, operations research, regional


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planning, sociology, psychology, probability, and statistics, together with the customary analytical tools

of engineering, are all used in training transportation engineers and planners. Figure 1-3 illustrates, in a

general way, the interdisciplinary breadth and the depth of involvement of transportation engineering.

Figure 1-3 Conceptual Outline of Interdisciplinary Training for Engineering Students (Khisty, 1981;

Wegman and Beimborn, 1973). The upper-left part of this figure traditionally represents the "soft" side

of transportation engineering, and the lower-right side, representing pavement design, bridge

engineering, and drainage, may be looked on as the "hard" side of transportation. However, there is no

definite demarcation between the two.

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1.4 The Systems Approach in Transportation Engineering

The systems approach represents a broad-based and systemic approach to problem-solving that

involves a system. It is a problem-solving philosophy used particularly to solve complex problems. A

system is a set of interrelated parts, called components, that perform a number of functions in order to

achieve common goals. System analysis is the application of the scientific method to the solution of

complex problems. Goals are desired end states. Operational statements of goals are called objectives;

these should be measurable and attainable. Feedback and control are essential to the effective

performance of a system. The development of objectives may in itself involve an iterative process.

Objectives will generally suggest their own appropriate measures of effectiveness (MOEs). An MOE is a

measurement of the degree to which each alternative action satisfies the objective. Measures of the

benefits forgone or the opportunities lost for each of the alternatives are called measures of costs

(MOCs). MOCs are the consequences of decisions. A criterion relates the MOE to the MOC by stating a

decision rule for selecting among several alternative actions whose costs and effectiveness have been

determined. One particular type of criterion, a standard, is a fixed objective: the lowest (or highest) level

of performance acceptable. In other words, a standard represents a cut off point beyond which

performance is rejected (Cornell, 1980). With reference to communities, we often find a set of

irreducible concepts that form the basic desires and drives that govern our behaviour. To these desires,

the term values is assigned. Values form the basis for human perception and behavior. Because values

are shared by groups of people with similar ties, it is possible to speak of societal or cultural values.

Fundamental values of society include the desire to survive, the need lo belong, the need for order, and

the need for security. A policy is a guiding principle or course of action that is adopted to progress

toward an objective. Evaluating the current state of a system and choosing directions lor change may be

considered as policymaking. Steps in System Analysis

1. Recognize community problems and values.

2. Establish goals.

3. Define objectives.

4. Establish criteria. '^^IIIJIIPP^


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5. Design alternative actions to achieve steps 2 and 3.

6. Evaluate the alternative actions in terms of effectiveness and costs.

7. Question the objectives and all assumptions.

8. Examine new alternatives or modifications of step 5.

9. Establish new objectives or modifications of step 3.

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10. Repeat the cycle until a satisfactory solution is reached, in keeping with criteria, standards, and

values set.

A simplified system analysis process is shown in Figure 1-4. Figure 1-4 The System Analysis Process.

1.5 Transportation Policymaking

Engineers and planners also recognize that most transportation issues can be characterized by great

size, breadth, complexity, diversity, cost, and uncertainty. An example of a transportation system model

is shown in Figure 1-5. It consists of inputs, such as land, labor, and capital, fed into three subsystems:

(1) the physical subsystem, (2) the activity subsystem, and (3) the human subsystem.

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Figure 1-5 Transportation System Model: Transportation Processor (NHI, 1980). The physical subsystem

consists of vehicles, pavements, tracks, rights-of-way, terminals, and other manufactured or natural

objects. The activity subsystem includes riding, driving, traffic control, and so on. These activities

interface with the human subsystemindividuals and groups of people who are involved with the

physical and activity subsystems. Outputs from the system include the movement of people and goods

and improvement or deterioration of the physical environment.

1.6 Movement and Transportation

The reason that people and goods move from one place to another can be ex-plained by the following

three conditions:

(1) complementarity, the relative attractiveness between two or more destinations;

(2) the desire to overcome distance, referred to as transferability, measured in terms of time and money

needed to overcome this distance and the best technology available to achieve this; and

(3) intervening opportunities to competition among several locations to satisfy demand and supply.

How people and goods move from an origin to a destination is a matter of mode choice (a person might

choose to take the bus downtown rather than use her car), depending on such attributes as time, speed,


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Ubiquity

Mobility

Efficiency

Mode

Passenger Service

Freight Service

Highways

Very high: land owners have direct access to a road or street. Direct routing limited by terrain and land

use.

Speeds are limited by human factors and speed limits. Capacity per vehicle is low, but many vehicles are

available.

Not high as regards safety, energy, and some costs.

Truck

Negligible

Intercity, local, farm to processing and market centers. Small shipments; containers

Bus

Intercity and local

Packages (intercity)

Automobile

Intercity and local

Personal items only

Bicycle

Local: recreational

Negligible

Rail transport

Limited by large investment in route structure. Also constrained by terrain.


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Speed and capacity can be higher than for highway modes.

Generally high, but labor costs may result in low cost efficiency.

Railroads

Mostly < 300 miles and suburban commuters

Intercity. Mostly bulk and oversized shipments; containers

Rail transit

Regional, intracity

None

Air transporlt

Airport costs reduce accessibility. Excellent opportunity for direct routing.

Speeds are highest, but capacity per vehicle is limited.

Fairly low as regards energy and operating costs.

Air carriers

Mostly > 300 miles and across bodies of water

High-value freight (no bulk) on long hauls; containers

General aviation

Intercity; business, recreation

Minor

Water transport

Direct routing and accessibility limited by availability of navigable waterways and

Low speed. Very high capacity per vehicle.

Very high: low cost, low energy use. Safety varies.

Ships

Cruise traffic. Ferry service

Bulk cargos, especially petroleum; containers


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2.2.1 Governmental Participation

A characteristic of human social organizations is the establishment of a "government," which - in an

impartial sense - may be deemed as consisting of the rules of conduct, the collective decision-making

processes, and the means of enforcing the rules that attempt to impart social and economic order and

to maintain the cohesiveness of a society. The specific actions that a government takes at any given timeas well as the method by which it chooses to implement those actions reflect the contemporary value

system of the society it represents. Conceptually, there exist* a continuum of governmental forms

ranging from anarchy (i.e., complete lack of governmental intervention in the affairs of people) to

totalitarianism (i.e., complete control by government). Actual governmental structures lie somewhere

between the two extremes.

2.2.2 Instruments of Governmental Involvement

In rough outline, the typical ways by which the government intervenes in the market place to

accomplish objectives that, in its representational role, it finds to be in the public interest include

Soft promotion refers to attempts by the government to encourage or to discourage certain situations

without legally requiring them. (An advertising campaign favouring car-pooling aimed at reducing rush-

hour congestion and obviating the need for costly highway construction or as a strategy to reduce

energy consumption is an example of soft promotion.) Regulation refers to those government actions

that place legal requirements on individuals and firms to satisfy the public interest. (Transportation-related examples of regulation include the establishment of automobile bumper standards to reduce

fatalities, automobile air-pollution-emission standards to improve environmental quality, and engine-

efficiency standards to conserve energy. Other examples include the regulation of airline route

structures to ensure the availability of service to all and the regulation of the rates that trucking

companies can charge their customers.)

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Investment involves me financial support, public financing, or even public ownership of various systems

or services. (Subsidies to privately owned bus companies to ensure service to mobility-disadvantaged

groups, public ownership of highways lo maintain a comprehensive level of accessibility, and

participation in the construction of airports and harbours are but a few examples of investment actions)

2.3 Tools and Applications

The typical program of study in transportation engineering includes the basic sciences, mathematics,

and computer programming. The subject matter of those courses of study stresses the basic tools


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needed for work in the field of engineering. Transportation engineers employ models to study and

analyze the systems of concern. A model may be defined as the representation of a part of reality. Static

models represent the structure of a system, whereas dynamic models also incorporate a representation

of the system's process, that is, the way in which it changes over lime.

2.4 The Role of Transport in Society

Transport plays a very important role in general development of the country, especially economic

development. In a developing country, the goal of industrial development can only be achieved through

an efficient transportation system of wide and varied nature. Social, cultural and political institutions as

well as the life of the people can be enriched through an efficient transportation system. Transportation

aids in the exploitation of natural resources like minerals, water, resources, forest and agricultural

resources. The transportation systems in common use around the world comprise distinct services such

as railways, roads, shipping, inland water transport, airlines, ropeways and pipe lines. Advance

transportation planning is necessary in order to achieve proper coordination between the modes of

transportation; special emphasis has to be laid on

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2.5 Introducing Comprehensive Transport Planning

Every year the number of vehicles using the roads increases, yet the road network is not keeping pace

with the growth of traffic leading to increased congestion. At the same time, there is increasing public

opposition to the construction of new roads - which in most cases, almost inevitably, are

environmentally undesirable. This apparent impasse is to some extent due to a misconception of the

real objective. The need is not for the provision of bigger and better roads to cope with more and 'more

vehicles.

2.5.1 Redefining the Objective

The real objective is the movement of people and goods - not necessarily the movement of vehicles.

Having redefined the objective the problem changes too. People can be moved by car or by public

transport - they could even walk, but this is increasingly unlikely for other than short distances! For

some movements the car is ideal, for others the bus or other mass transit mode is preferable.

Comprehensive transport planning is about the optimization of the balance between the uses of these

modes. For inter-urban travel the flexibility of the car is a major advantage. For leisure trips in urban

areas too, this flexibility is importantand the destinations of leisure, and other non-work, trips are

often widely spread in both space and time, reducing their impact on congested streets. It is for thejourney to work that public transport is most appropriate. The journey from home to work occurs in a

short peak period each morning and is, of course, largely repeated in reverse each evening. Many trips

terminate in relatively few locations - the town centre, the industrial area, etc. As car occupancies

average around 4 persons and buses can carry at least ten times more people per length of road lane, a

partial remedy is clear. Some trips from home to work must be attracted, or diverted, to public

transport.


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2.5.2 The 'Carrot' and the 'Stick'

Bus travel, however, is not popular with commuters, because services are too often unreliable, slow,

and uncomfortable and crowded, whereas a car is at least thought to be convenient and reliable. The

change of mode must therefore be induced. This requires the use of both 'the carrot' and 'the slick'.

First, 'the carrot' - bus services must be improved, in reliability, in frequency and in convenience. Buspriority measures of one form or another can usually do a lot to meet these requirements.

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But the carrot alone is nor enough, the car will still be preferred, so 'the stick' - restraint measures -

must be applied. This means making the use of the car less attractive, by providing fewer parking spaces

at higher cost, by closing streets to cars, or just by allowing congestion to take effect. Perhaps even, at

some later date differential road-use pricing or supplementary licensing could be applied, although

there are operational problems in both cases. The movement of goods in urban areas however is not

something which can readily be transferred to other transport modes. The lorry is here to stay. But the

'juggernauts' engender much of the emotional outcry in many areas, most notably in residential streets

in towns and small villages on through-routes. Here, palliate measures may be appropriate - directing

large lorries onto certain preferred routes, providing lorry parks in non-residential areas, or even

perhaps, providing 'trans-shipment' depots outside town areas. However, no matter what is done to

induce people to change their travel mode, or goods vehicles to change their routes, there will

eventually still be congestion on many roads. Before new roads are built, it is plain that the existing road

system should be used as fully as possible. And this means, among other things, using roads for

movement instead of for parking. Other typical traffic-management measures to improve on the use of

existing roads, to move people rather than vehicles, might include some or all of the following:

-area roads

- bus-only lanes etc.

-way systems

-turn bans

-hour urban clearways.

After consideration of all of these however, and the application of appropriate measures - which formthe basis of the relatively short-term management aspects of urban planning - there will still be a need

for some new roads. And these have to be planned.

2.5.3 Comprehensive Planning

Transport planning for a county - not Just town or rural area in isolation, but both together - must be

comprehensive, and based on financial realism (there is NEVER enough money). The roles of public


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transport, private car restraint, traffic management measures, and new road construction need to be

fully integrated to derive the best use of the inevitably limited resources. A transport plan is developed

as a complete package of projects and policies, conceived as a unified whole. It should be implemented

comprehensively in across-the-board stages in accordance with a carefully conceived, financially

realistic, annual programme, derived in turn from a longer programme.

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Outside the urban areas, less important inter-urban and other rural roads are often planned on the basis

of simple growth factors.

2.5.4 The Transportation Study

In larger urban areas, the medium-term planning of future transport systems is usually based on a

transportation study - sometimes called a land-use transportation study because of its fundamental

reliance on the relationships between land use and travel demand. A transportation study is basically a

computer-dependent mathematical process, founded on present-day observation, whereby futuretravel patterns can be predicted. In essence, the transportation study process consists of:

a) Surveying the present-day travel habits of people living and/or working in the specified area,

b) Developing mathematical formulae which, given details of household structure, income, car

ownership, etc. in the study area, can reproduce present-day travel patterns as surveyed. The formulae

(or 'models') in their simplest form are basically:

i) trip-end prediction - determining how many trips leave a zone e.g. a group of households,

ii) Trip distribution - determining the destination of these trips,

iii) Modal split - determining the mode of travel - car or bus,

iv) Assignment - determining the actual roads used,

c) Using these formulae, together with predicted values for future population, incomes, etc. to predict

future travel patterns,

d) Comparing the merits of alternative transport systems to accommodate the predicted movements.

SUMMARY a) The objective of comprehensive transport planning is the optimum movement of people

and goods. b) Particularly for the journey to work, public transport could be more efficient than theprivate car - but is less attractive. c) To induce greater use of public transport the system needs to be

improved and restraint applied to the use of the private car.

24

d) County transport planning should be done on a comprehensive basis, developing integrated packages

of public transport, private car restraint, and the optimum use of both existing and new roads. e) In


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larger urban areas, transport planning is usually based on a transportation study - a means of predicting

future travel movements. f) The preferred strategy, which is not just a collection of unrelated schemes,

is best developed by optimization from a range of integrated possible packages. g) The final choice of

strategy is a political matter.

2.6 Transportation Systems, Hierarchies, and Classification

The classification of transportation modes into different operational systems or functional classes is

useful in understanding the complexity of the total transportation system. The classification system

adopted for transportation covers

These help to distinguish both the functional and hierarchical characteristics of the elements of the road

transportation systems.

2.6.1 Traffic Classification Systems

Two classification systems are used for road traffic as follows:

a) Functional classification systems

b) Loading classification systems

The Functional Classification Systems classifies traffic according to its major functions. Traffic is further

sub-divided into Motorised Transport (MT) and Non-motorised Transport (NMT) traffic. MT traffic

includes vehicles which derive their motive power from a motor (engine) and include all categories ofmotor vehicles/cycles. On the contrary, NMT traffic derives its power from either human or animal

effort and include pedestrians, pedal cycles and carts. Functional classification of traffic includes (but not

limited to) the categories listed in the table below.

25

Categories

Description

A. Motorised Traffic

Passenger vehicles

Motor cycle/Scooter Car (sedan, special wagon) Jeep/4-wheel Drive Taxi/minibus Large bus

Goods vehicles


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Pick-up Light goods (3.5t unladen weight) Medium goods (2-axle, >3.5t) Heavy goods (3, 4-axle)

Articulated/draw-bar trucks

B. Non-motorised Traffic

Pedestrian Pedal cycle Cart (Human/animal drawn)

Loading classification systems are concerned with the characteristic design loading as derived from the

projected traffic demand for commercial vehicles. This is normally expresses in expected repetitions of

equivalent standard axles (ESA) over the selected design period. A standard axle weighs 8160kg and the

value for ESA is computed against this loading as follows: Where L = measured axle load N = exponential

factor, varies with axle load. Kenya adopted 4.5 Typical load classification systems are tabulated below:

Kenya RDM-III Materials and Pavement Design for New Roads

UK Road Note 13 (Pavement Design for Roads in Tropical and Sub-tropical Countries)

Class

ESA x 106

Class

ESA x 106

T1

2560

T1


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T4

13

T4

1.53.0

T5

0.25 - 1

T5

3.06.0

T6

6.010

T7

1017

T8

17 - 30

26

2.6.2 Road Classification Systems

Roads are generally classified from their functional aspects. They have two basic traffic service functions

which, from a design standpoint, are incompatible. These are:

a) to provide traffic mobility between centres and areas

b) to provide access to land and properties adjoining the roads

Roads are grouped into Urban and Rural road systems Over the course of time many roads have become

multi-functional, i.e. they now act as (a) Carriageways for through vehicular traffic, (b) Access ways to

frontage properties, (c) Routes for public transport; (d) Parking spaces for vehicles, (e) Passageways forpedestrians and cyclists, and (f) Corridors for the location of water/sewerage/gas/electrical services.

(a) Rural road systems

A major feature of the car-oriented transport plans of the 1950s in the United States was their

clarification and prioritization of die transport functions served by various types of road. In essence they

divided roads into three main functional groups: 1. Arterial roads which are primarily for longer-distance


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high-speed through-vehicle movements and, hence, provide minimal access to adjacent frontages 2.

Local roads and streets whose main function is to provide for frontage access and, thus, whose design

and traffic management is intended to discourage through traffic 3. Collector roads, i.e. the 'middle'

group, which are intended to provide for both shorter through-vehicle movements and frontage access.

Arterial roads are subdivided according to whether they are limited access (e.g. freeways) with no direct

frontage access whatsoever, major arterials (e.g. expressways) which have small amounts of frontage

access, and minor arterials which have more frontage access. Local streets are generally subclassified

according to the land use that they serve, e.g. residential, commercial, and industrial streets. Collector

roads are described as major or minor, depending upon their relative amounts of through and access

service. An illustration of a functionally classified rural highway network is shown in Figure 1-9.

27

Figure 1-9 Schematic Illustration of a Functionally Classified Rural Highway Network (AASHTO,2001).

Figure 1-10 shows a functionally classified suburban street network Figure 1-10 Schematic Illustration of

a Portion of a Suburban Street Network (AASHTO,2001).

28

In Britain non-urban roads are described according to function as being either primary routes or

secondary roads. Primary route, distinguished by direction signs with a green background, are mainly

trunk roads (which include most motorways) and some local authority roads. In Kenya, roads are

grouped into 5 main classes according to the major function in the network. A sixth category of special

purpose roads is also in use based mainly on the source of funding and responsibility for maintenance.

The Kenya road classification system is as follows:

Main Class

Description/Function

(I) Primary Roads

Class A : International Trunk Roads

Linking international centres and crossing international boundaries or terminating at international ports

Class B: National Trunk Roads

Linking nationally important centres (Principal towns and urban centres)

Class C: Primary Roads

Linking provincial centres to each other or to higher class roads (urban and rural centres)

(II) Secondary/Rural Access Roads

Class D: Secondary Roads


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Roads linking locally important centres to each other, to more important centres or to higher class roads

(rural/market centres)

Class E: Minor Roads

Any road link to a minor centre (market/local centres)

Special purpose roads

R (Government access roads)

Roads providing access to government facilities

T (Tea) roads

Roads in tea growing zones and maintained with funds from tea cess

C (Coffee) roads

Roads in coffee growing zones and maintained with funds from tea cess

W (wheat) roads

Roads in wheat growing zones and maintained with funds from tea cess

L (adjudication/Settlement) roads

Roads in settlement areas

Classes A and B mainly provide mobility. Class E and below mainly provide access. C and D (for all

practical purposes) have to provide both mobility and access, with emphasis on mobility for class C and

access for class D. These roads are the most difficult to design as far as traffic safety and operation are

concerned.

29

(b) Urban road systems

A series of distinct travel movements are recognizable in most trips. On a highway system, for example,

these movements are a main movement along a freeway, a transition to an arterial via a freeway off-

ramp, then further movement along an arterial where traffic is distributed and later collected via a

collector, finally accessing a terminal (a garage or on-street parking lot). Further movement of the

passenger may be as a pedestrian on a sidewalk of a local street, and finally to his or her destination.

Figure 1-8 shows this hierarchy of movement. The inadequacy of parts of the hierarchy to accommodate

each trip movement is one of the reasons that systems fail or become obsolete. Figure 1-8 Hierarchy of

Movement (AASHTO, 2001). Urban roads are designated ias


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1. Primary distributors which are intended to serve a town as a whole by linking its business, industrial,

and residential districts,

2. District distributors which feed traffic from the primary network to environmental districts (e.g. town

centres or industrial estates, or large residential districts) but do not traverse them, and

3. Local distributors which allow traffic from the major distributors to penetrate environmental districts

and.

4. access streets which provide access to homes, businesses, factories, etc

Table 1.5 summarises the various functions and features of these urban roads; also included in this table

are details regarding a class of street which has come to prominence in more recent years - the

pedestrian street

30

31

Table 6.5 Hierarchical classification system for urban roads based on function

Pedestrian streets

Access roads

Local distributors

District distributors

Primary distributors

Predominant activities

Walking; meeting; trading

Walking; vehicle access; delivery of goods and servicing of premises; slow-moving vehicles

Vehicle movements near beginning or end of all journeys; bus stops.

Medium distance traffic to Primary Network; public transport services; all through traffic with respect to

environmental areas

Fast-moving long-distance traffic; no pedestrians or frontage access

Pedestrian movement

Complete freedom; predominant activity

Considerable freedom with crossing at random


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Controlled with channelised (e.g. zebra) crossings

Minimum pedestrian activity with positive measures for their safety

Nil; vertical segregation between vehicles and pedestrians

Stationary vehicles

Nil, except for servicing and emergency

Some, depending on safety considerations

Considerable, if off-road facilities not provided

Some, depending on traffic flow conditions

Nil

Heavy goods vehicle activity

Essential servicing and frontage deliveries only

Residential-related activities only; other areas - delivery of goods and services

Minimum through trips

Minimum through trips

Suitable for all HGV movements, especially through trips

Vehicle access to individual properties

Nil, except for emergency vehicles and limited access for servicing

Predominant activity

Some, to more significant activity centres

Nil, apart from major centres, i.e. equivalent to local distributor level of vehicle flow

Nil, apart from sites of national traffic importance

Local traffic movements

Nil, but may include public transport

Nil

Predominant activity


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Some - only a few localities may be severed, and junction spacing is important

Very littlejunction spacing will preclude local movements

Through traffic movements

Nil

Nil

Nil

Predominant role for medium-distance traffic

Predominant role for long-distance traffic

Vehicle operating

Less than 5 km/h;

Less than 32km/h

Subject to 48 km/h

Subject to 48 or 64

More than 64 km/h

32

speeds/speed limits

vehicles enter on sufferance

(20 mile/h) with speed control devices

(30 mile/h) limit but layout should discourage speed

km/h (30 or 40 mile/h) limit within the built-up area

(40 mile/h) depending on geometric constraints

33

3 TRAFFIC ENGINEERING

3.1 Definition

The Institute of Traffic Engineers defines traffic engineering as: "that phase of engineering which deals

with planning, geometric design and traffic operations of roads and streets and highways, their


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networks, terminals, abutting lands, relationships with other modes of transportation for the

achievement of safe, efficient and convenient movement of persons and goods." The definition

contained in the Glossary on Traffic Engineering Terms of the PIARC is: "That phase of engineering which

deals with the planning and geometric design of streets, highways and abutting lands, and with traffic

operation thereon, as their use is related to the safe, convenient and economic transportation of

persons and goods." The above definitions adequately illustrate the scope of the subject.

3.2 Growth of the Subject of Traffic Engineering

Traffic engineering is a branch of engineering that has grown with the increase in traffic in recent years.

As vehicular traffic began to increase, the congestion on the streets began to hamper the safe and

efficient movement of traffic. Accidents, parking problems and environmental pollution began to be felt.

It became necessary to give more attention to the operational characteristics of highway transportation

and study the need for better geometric design, capacity, intersections, traffic regulations, signals,

traffic signs, and roadway markings, parking facilities, design of bus stands and truck terminals and

street lighting. The Traffic Engineer is expected to deal with the above specialised needs The profession

of Traffic Engineering evolved mainly in America which experienced the high growths in automobiles.

The now familiar three-colour light signals made their appearance in 1918. The Institute of Traffic

Engineers was founded in 1931 and with this the profession was officially established and defined.

Highway Engineering and Traffic Engineering are related subjects, and the latter can be deemed to be an

offshoot of the former. Traffic Engineering is now recognized as a specialised branch.

3.3 Functions Traffic Engineer

The functions of a Traffic Engineer include the following:

1. Collection, analysis and interpretation of data pertaining to traffic. [ Organise and implement varioussurveys and studies to collect data on traffic characteristics,] including (i) origin and destination survey,

(ii) volume counts, (iii) speed, travel time and delay measurements, (iv) accident statistics, (v) parking

characteristics, (vi)

34

pedestrian behaviour and use of streets, (vii) capacity studies and (viii) economic analysis for traffic

facilities.

2. Traffic and transportation planning. [Preparation of traffic and transportation plans to ensure a safe,

orderly and fully integrated transportation system]. This phase is concerned with the land use-transportation relationship and travel characteristics.

3. Traffic design. [Geometric design of highways and streets], includes inter-section design, schemes for

grade separated inter-changes, design of off-street and on-street parking facilities and design of

terminal facilities for trucks and buses. In geometric design, the functions of the highway engineer and

the traffic engineer overlap.


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4. Measures for operation of traffic. [For efficient and safe operation of traffic], the traffic engineer has

to take recourse to a number of measures such as:

(i) Legislation and enforcement - for regulation of the driver, vehicle and road. (ii) Management

measurese.g. one-way streets, prohibited turnings at junctions and tidal flow arrangements, exclusive

bus lanes etc. to maximise use out the available street facilities. (iii) Measures for regulation of parkingof vehicles. (iv) Traffic control devices, e.g. traffic signs, traffic signals, pavement markings and

channelization techniques, for safe and efficient flow of traffic.

5. Administration. [Organise and administer various programmes to secure safe and efficient traffic in

towns and cities]. Close association with legal and administrative framework of the citys department

dealing with education, legislation and enforcement measures.

1-4. Organisation of the Traffic Engineering Department With the growth of the vehicular traffic on the

roads, it is increasingly realised that the organizational set-up designed to deal with the attendant

problems of growing traffic has to be a separate unit under competent traffic engineers. The need for

such a unit exists at the National and city levels.

35

4 SPEED, JOURNEY TIME AND DELAY SURVEYS

4.1 Definitions

Speed is the rate of movement of traffic or of specified components of traffic and is expressed in metric

units in kilometres per hour (KPH).

1. Spot speed is the instantaneous speed of a vehicle at a specified location

2. Running speed is the average speed maintained by a vehicle over a given course while the vehicle is in

motion.

i.e. Running speed = Distance / Running time = Distance / (Journey timedelay)

3. Journey speed (or overall travel speed) is the effective speed of a vehicle between two points. Thus:

Journey speed = Distance / Total journey time (including delays)

4. Time-mean speed is the average of the speed measurements at one point in space over a period of

the time. It is the average of a number of spot speed measurements.

5. Space-mean speed is the average of the speed measurements at an instant of time over a space.

4.2 Use of Speed, Journey Time and Delay Studies

Spot speed measurements are required for:


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ic elements such as horizontal

curvature, vertical profile, sight distances and super-elevation.

peed and accidents

-and-after studies of road improvement schemes

Journey speeds and delays are required:

ate congestion, capacity, level of services in a network

36

of traffic control devices

4.2.1 Methods of Measuring Spot Speeds

The methods available for measuring spot speeds can be grouped into:

(a) Those that require observation of the time taken by a vehicle to cover a known distance. These are

further classified into long base and short base.

The long base methods commonly used are: (i) Direct timing, (ii) Enoscope and (iii) Pressure contact

tubes. Short-base method uses vehicle detectors over a short distance.

(b) Radar speed meter which automatically records the instantaneous speed

(c) Photographic method

Factors to be considered while selecting the site for the survey are:

1. The purpose for which the data are required. E.g. in accident pattern studies

2. Minimize the influence of the study team and equipment on the vehicle speeds.

3. Generally straight, level and open sections of highways

4.2.2 Direct-Timing Procedure for Spot Speed Determination


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Two reference points are marked on the pavement at a suitable distance apart and an observer starts

and stops and accurate stop-watch as a vehicle crosses these two marks. From the known distance and

the measured time intervals speeds are calculated. Large errors are likely due to parallax.

4.2.3 Radar Speed Meters

These meters work on the Doppler principle. The instrument is set up near the edge of the carriage way

at a height of about 1m, above the ground level. The speeds of vehicles in both directions can be

observed by this method. The device has been extensively used for traffic engineering studies as well as

for enforcement by traffic police.

4.2.4 Photographic Method and Video Camera Method

Time-lapse camera photography can be used to determine the speeds of vehicles in crowded streets.

Photographs are taken at fixed intervals.

37

Images by video cameras can also be used.

4.2.5 Methods for Measurement of Running Speed and Journey Speed

The methods commonly used for measuring running speed and journey speed are: (i) Moving observer

method (ii) Registration number method (iii) Elevated observer method. These methods are described in

detail in the following sections.

(a) Moving Observer Method

The speed and flow can be obtained by travelling in a car against and with the flow, and noting downthe journey time, the number of vehicles met with from the opposite direction, and number of vehicles

overtaking the test vehicle. Preferably even two cars are required, each carrying a driver and three

observers. One observer in the car counts opposing traffic, another carries a journey log prepared in

advance. The log records the traffic counts and times at predetermined points en-route, together with

stopping and starting at intersections. Advantages of the method

journey time. Hence it is

economical in manpower.

ons, delays, parked vehicles etc.

(b) Registration Number Method


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Observers are stationed at the ends of a measuring section, about 0.51.0 km long. The time and

registration number of the vehicles entering and leaving the section are noted using synchronized

watches.

(c) Elevated Observer Method

Observers stationed on top of an elevated building

38

5 VEHICLE VOLUME COUNTS, CLASSIFICATION AND OCCUPANCY

5.1 Need for Vehicle Volume, Classification and Occupation Counts

The volume of traffic using a road system, also termed as flow, is expressed in vehicles per hour or

vehicles per day. When the traffic is composed of a number of types of vehicles, it is the normal practice

to convert the flow into equivalent passenger car unit (PCUs), by using equivalency factors. The flow is

then expressed as PCUs per hour or PCUs per day. It is important to know the vehicular volume using a

road network in order to compute the current efficiency of the system and the quality of service offered

to the road users. Traffic forecasting is an important step in the transportation planning process if traffic

flow data are available over the past number of years, the rate at which traffic flow has increased in the

past can be easily determined. A reasonable indication of the future traffic growth rate is obtained by

extrapolating the past trends into the future. The annual vehicle-kilometres of travel for a road section,

as used accident studies, can be computed using data on the average annual flow and the length of the

highway. The structural design of the road pavement requires data on the number of commercial

vehicles using the road. Though more accurate analysis demands data pertaining to the axle load

spectrum and repetitions, the number of commercial vehicles using the road will itself be a good guide

in pavement design. The programming of the maintenance needs of a highway is often based on the

traffic using the road. Traffic regulatory and control systems are designed on the basis of accurate

vehicle flow data. The design of signals and road junctions are possible only if, among other things, the

vehicle flow data are available. The ultimate aim of travel is to transport people and goods.

5.2 Types of Counts

The three common levels of measurement of vehicle flow are: (i) Average annual flow, expressed in

vehicles per year. (ii) Annual Average Daily Traffic (AADT), expressed in vehicles per day. (iii) Hourly flow,

expressed in vehicles per hour. The average annual flow measurement is useful for estimating the total

travel on a road system and for determining the gross annual revenues from road users. In accidentstatistics the total annual vehicle-kilometres forms the usual basis for comparison. The A.A.D.T., which is

1/365th of the total annual flow, is a common measure of flow utilized in geometric standards for

highways, improvement of existing facilities and standards for pavement design and maintenance. If the

flow is not measured for all the 365 days, but only for a few days the average flow is known by the term

ADT, Average Daily Traffic.

39


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Short term variations occurring in the course of a day and especially the peaking situations in the

morning and evening rush hours are needed for design of traffic control systems and complicated

intersections.

5.2.1 Short term and long term counts

The duration of the counts depends upon the purpose for which the data are needed and the financial

and man-power resources at the command of the traffic engineer. Sometimes it is only necessary to

measure the flow for a short term, say an hour; at other times the flow may be measured for an

intermediate period such as a full day of twenty-four hours; in some situations, the count may extend

for a duration of a full week; and lastly, the count may be a continuous and regular affair.

5.2.2 Method Available for Traffic Counts

The methods available for traffic counts are listed below:

(a) Manual methods

(b) Combination of manual and mechanical methods

(c) Automatic devices.

(d) Moving observer method.

(e) Photographic methods.

Manual Methods The advantages of manual methods and situations where these are to be preferred

are:

a) Details such as vehicle classification and number of occupants can be easily obtained.

b) The data can be collected giving the breakdown of traffic in each direction of travel.

c) Specific vehicular movements at a junction can be noted and recorded.

d) Manual methods enable any unusual conditions obtaining at the time of the count to be recorded.

e) In developing countries, sophisticated automatic devices are not indigenously produced.

f) Pilferage and vandalism often prevent the use of costly equipment in remote rural areas, and in such

cases manual methods are the only solution.

g) Even if automatic devices are used, it is often necessary to check the accuracy of these devices

periodically and manual methods serve this purpose.

h) Data accumulated by manual methods are easy to analyse.

i) Manual methods are suitable for short-term and non-continuous counts.


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The advantages of automatic devices and situations dictating their use are:

a) Where a continuous and regular record of traffic flow is needed, the only alternative is to install

automatic counters.

b) Their use has been very wide-spread in the developed countries, where traffic engineering and

transportation planning have attained a high degree of perfection.

c) If counts of remote areas are needed, automatic devices are useful.

d) Automatic devices usually yield data which are amenable to easy analysis by computers.

The number of observers needed to count the vehicles in manual methods depends upon the number of

lanes in the highway on which the count is to be taken and the

40

type of information desired. The equipment required includes a watch; Pencils, eraser and pencilsharpener; Supply of blank field datasheets; and Clip board. Combination of Manual and Mechanical

Method An example of a combination of manual and mechanical methods is the multiple pen recorder.

A chart moves continuously at the speed of a clock. Different pens record the occurrence of different

events on the chart. Automatic Devices The automatic devices essentially consist of equipment for

detecting the passage or presence of a vehicle (called detector or sensor) and another for recording the

count. The sensor usually transmits some form of electric impulse which activates the accumulating

register or recording chart. They are:

i) Pneumatic tube (road tube)

ii) Electric contact.

iii) Co-axial cable.

iv) Photo-electric.

v) Radar.

As regards whether the counting programme should be continuous or only for a short duration, here

again the prime consideration is cost. At least a 7-day count once or twice a year would be all that one

could think of in the developing countries. The Kenyan / U.K. practice is to measure the 7-day average

flow for 16 hours (6 am-l0pm) in the month of August, in which month average travel demands havebeen found consistently to be at their highest. For observations taken during any other months, average

adjustment factors are applied to convert them to their August equivalent. 50-Point traffic census in

Kenya: One of the examples of organised planning and programming for regular traffic census in any

country can be had in the 50-Point Traffic Census in Kenya.

5.2.3 Vehicle Occupancy Surveys


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Vehicle occupancy surveys are easy to conduct for cars and motorised two-wheelers. The observers can

note the number of occupants of every one of such vehicles by standing by the roadside. For buses, the

occupancy can be determined by examining the ticket sales. An Indian Study, covering 640 buses for

nearly two years, has concluded that the average occupancy of buses is 43 passengers, in addition to the

driver and the conductor.

5.3 Origin-Destination Survey

In a transportation study, it is often necessary to know the exact origin and destination of the trips and

the number of trips made. Other information yielded by the O-D survey includes land-use of the zones

of origin and destination, household characteristics of the trip-making family, time of the day when the

journeys are made, trip purpose and mode of travel.

41

Origin is defined as the place where the trip begins and destination is defined as the place where the trip

ends. Uses of O-D survey data are: (i) To determine the amount of by-passable traffic that enters a town(ii) To develop trip generation and trip distribution models in transport planning process. (iii) To

determine the adequacy of a highway system and to plan for new facilities. (iv) To assess the adequacy

of parking facilities and to plan for future. In the study of transportation problems of towns, big or small,

it is usually necessary to define external cordon lines, which are imaginary lines at the boundary of the

study area. In big towns, it may also be necessary to select some internal cordon lines, which may be

concentric rings. For checking the accuracy of survey data, it may be necessary to have screen-lines,

which are imaginary lines dividing the area into parts.

5.3.1 Survey Methods

Some of the methods available for conducting an O-D survey: (a) Home interview survey (b) Road-side

interview survey (c) Post-card questionnaire survey (d) Registration number plate survey (e) Tags on

vehicles.

5.3.2 Checking the Accuracy of O-D Survey Data

The data obtained from the home-interview survey is usually cross-checked with the data obtained from

screen-line and cordon counts.

5.3.3 Presentation of Results

O-D surveys yield a vast amount of data. To understand them it is necessary to present them inconvenient tabular or pictorial form. The most convenient form is an 0-D matrix, in which the origin

zones and destination zones are represented. The horizontal axis of the matrix represents the

destination zones and the vertical axis of the matrix represents the origin zones. The zones may be

further classified into internal and external zones if the survey covers both the internal and external

zones. The number of trips is entered in the cells of the matrix. The matrix is represented below.


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DESTINATION ZONES

INTERNAL

EXTERNAL

1

2

3

72

73

74

ORIGIN ZONES

INTERNAL

1

2-

3

42

EXTERNAL

72

73

74

In the above matrix T2-3 represents the number of trips originating in zone 2 and terminating in zone 3.

The most popular pictorial representation is by means of a desire line chart. In this chart, the trips

between any pair of zones are represented by a straight line connecting the centroids of the two zones

and having a band width drawn to a suitable scale to represent the actual volume of trips.

43

6 TRAFFIC REGULATION

6.1 Basic Principles of Regulation

6.1.1 Need for regulation of traffic


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The motor vehicle is a machine in the charge of a human being and this makes it necessary for the

formulation of suitable regulations for safe operation of traffic and enforcement of these regulations.

The regulations should have the following attributes:

so as to achieve safe and efficient movement of traffic and pedestrians, without undulyinfringing upon the individual rights of the road users.

nd times.

The traffic engineer should be conversant with the principles of regulation. The design of streets and

facilities and the safe operation of traffic are vitally connected with the Traffic Regulations.

6.1.2 Scope of traffic regulations

Traffic regulations cover matters dealing with the control of vehicles, drivers and road users. The control

of vehicles deals with the registration, weight, size, design, construction and maintenance. Driver

regulations deal with the licensing and other aspects of operation of vehicles by drivers. Regulation of

other road users deals with the rules regarding pedestrians, cyclists and motorcyclists. In Kenya, traffic is

mixed in character, and this brings in the need to regulate the movement of animal drawn vehicles,

bi/tricycles and hand carts.

6.1.3 Traffic laws

Most of the countries have uniform traffic laws operating in all parts of the country so that the laws are

understood consistently everywhere and are obeyed. In U.S.A., the Uniform Motor Vehicle Code serves

as a pattern for the States to evolve their own system of traffic laws. Many States have laws in

conformity with the Motor Vehicle Code, and some others have rules similar to those contained therein.

The Uniform Vehicle Code has the following five Acts: Act I. Uniform Motor Vehicle Administration,

Registration Certificate of Title and Anti-theft Act. Act II. Uniform Motor Vehicle Operator's and

Chauffeurs Licence Act. Act III. Uniform Motor Vehicle Civil Liability Act.

44

Act IV. Uniform Motor Vehicle Safety Responsibility Act. Act V. Uniform Act regulating Traffic onHighways. In U.K., the Road Traffic Act 1972 provides the framework for rules regarding the traffic

regulations. It is divided into the following parts: Part I. Principal Road Safety Provisions. Part II.

Construction and Use of Vehicles and Equipment. Part III. Licensing of drivers of vehicles. Part PV.

Licensing of drivers of heavy goods vehicles. Part V. Driving Instruction. Part VI. Third Party Liabilities.

Part VII. Miscellaneous and General. In Kenya, The Traffic Act. 1993, provides the basis for regulating

vehicles, drivers, other road users and traffic. It contains the following Chapters: Part l Preliminary. Part


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II Registration of Vehicles Part III Licensing of Vehicles. Part IV Driving Licences . Part V Driving and Other

Offences Related to the Use of Motor Vehicles. Part VI Regulation of Traffic Part VIA Designated Parking

Places Part VIB Parking Elsewhere than Designated Parking Places Part VII Accidents Part VIII Suspension,

Cancellation and Endorsement of Driving Licences Part IX Offences by Drivers of Vehicles Other than

Motor Vehicles and Other Road Users Part X Miscellaneous Provisions as to Roads Part XI Public Service

Vehicles Part XII General The act is applicable throughout Kenya.

6.2 Regulation of Speed

6.2.1 Need for regulation of speed

High speeds are always associated with accidents. Regulation of speed is one of the means of ensuring

safer travel.

6.2.2 General principles governing application of speed limits

Speed limits selected should be 'realistic' so that they are not disregarded by the drivers. Hence they

should be appropriate to conditions at site. Limits should be reviewed periodically based on

accumulated experience and future needs. The limits should be related to the volume and character of

traffic, the presence of pedestrians, the general features of the road and safety built into it and the

development that has taken place along the road.

45

6.2.3 Speed limits in urban areas

Speed limits in urban areas are governed by the type and volume of traffic. Chances of accidents are

increased urban areas due to mixed traffic conditions, with NMT traffic (Pedestrians and cyclists)

competing for space with MT traffic. Parking is also frequent along the streets, presenting another

source of accidents. The need for speed limit under these conditions is clear. In UK, the principal urban

limit is 30mph, though in some areas a limit of 40mph has been introduced. The definition of the urban

area in UK is accepted as any area provided by street lighting. In the USA, the Uniform Vehicle Code

prescribes an absolute speed limit of 30mph in any urban district. Many States observe speed limits of

25 to 30mph in residential districts and 20 to 25mph in business districts. In Kenya the traffic is mixed in

character. The street pattern in many towns is characterised by narrow and winding access alleys with

buildings abutting the carriageway. Pedestrian traffic is often heavy. The need for regulation of speed is

paramount. The speed limits on urban traffic vary with the nature of congestion and the type of streets.

Table 171 gives some general guidelines from a developing country

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Table 171 Speed limits for different types of vehicles under mixed traffic condition

Different categories of road and streets

Speed limits in kilometres per hour


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Group I

Group II

Light and Medium vehicle

Heavy vehicles

Major Roads of Arterial/Sub-arterial character mostly in open and thinly built-up areas

50

40

Roads with moderate traffic situated in semi-built-up areas.

40

30

Congested roads in built-up Areas.

30

20

6.2.4 Speed limits in rural areas

On rural highways, the speed limits normally imposed are 80kph, 100kph and 110kph. The US Uniform

Vehicle Code recommends a speed limit of 60mph for locations other than urban areas during the day

time. In UK, certain rural sections of motorways used to have an upper speed limit of 70mph, till

recently when the energy crisis forced the Government to reduce this. Single carriageway rural roads in

U.K. operate on speed limits of 50mph or 60mph.

6.2.5 Problem of Small Villages along Rural Highways

Small villages located along rural highways have peculiar safety problems. Since people may live on

either side of the road, frequent crossing of the road by pedestrians is unavoidable. Speeding vehicles

can cause hazardous conditions for these pedestrians. In such situations, the speed limits will have to be

set based on accidents records and the extent of local traffic. Note: It may be preferable in the long run

to re-route the road to bypass the villages as they grow into small towns.

6.2.6 Speed limits for different types of vehicles

Limits for speed of different classes of vehicles are also important. In UK, on all purpose roads, vehicles

which carry goods are subjected to a speed limit of 40mph and buses and coaches to 50mph. If trailers

are towed, the speed limit is 10mph lower. On motorways, as a rule, no speed limits for vehicle classes


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apply. A typical schedule of speed limits for different types of vehicles is given in Table 17-2. Table 17-2

Speed limits generally followed in Kenya/India for rural highways

Classes of Vehicles

Maximum

47

Speed k.p.h.

1.

Vehicles without trailers

(() Light motor vehicle or a motor cycle

No limit

(ii) Medium or heavy passenger motor vehicle

60

(in) Medium or heavy goods motor vehicle

60

2.

Articulated heavy motor vehicle

50

3.

Vehicle drawing not more than one trailer

(i) Vehicle being a light motor vehicle, and trailer being two-wheeled having a laden weight not more

than 800 kg

60

(ii) Vehicle being a light motor vehicle, and trailer having more than two-wheels or a laden weight more

than 800 kg

50

(iii) Vehicle being a medium motor vehicle

50


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Casualty rate (6)

30

85th percentile speed of cars not greater than 37 M.P.H.

(i) Built-up area on both sides (ii) Direct access from development on sides (iii) Presence of schools,

recreational grounds and playing fields

(i) High proportion of 2-wheeled vehicles (ii) Large number of pedestrians

(i) Frequent junctions with visibility inadequate for speeds greater than 30 M.P.H. (ii) Pedestrian cross-

ings (iii) Development close to footways

Above 5 per million veh. Miles (average of last years for fatal, serious and slight injuries).

40

85th percentile speed of cars not greater than 47 M.P.H.

(i) Built-up area as above (ii) Partially built-up, transition between built-up and rural (iii) Little or no

frontage development

(t) As above, but with more severe parking restrictions (ii) 2 - wheeled vehicles and pedestrians more

numerous

(t) Important radial or ring roads with well designed footpaths on both sides (ii) Footways provided

roads of adequate capacity and well designed. (iii) Roads such as urban motorways where geometric

design is based on 40 M.P.H. speed.

(i) Above 3 per million veh. Miles for all types of injury. (ii) Above 1 per million veh. Miles for fatal injury.

(iii) Above 1 per million veh miles for pedestrians and drivers two-wheeled vehicles.

50

85th percentile speed of cars not less than 40 M.P.H. and not greater than 57 M.P.H.

(i) Rural roads less de-veloped than 40

(ii) But having above average casualty rates.

(i) Application to single carriageway roads of two or three traffic lanes, not

Fatal and serious casualty rate per million vehicle miles normally

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Appropriate Speed (M.P.H.) (1)


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limits for speed zoning are (Ref. 9): (i) Complete engineering investigations. (ii) Study of accident

frequency, (iii) Number of business establishments on street. (iv) Volume study (v) Speed study. (vi)

Observation by police department. (vii) Width of street (viii) Pedestrian traffic volume.

(a) Speed zoning at horizontal curves

The safe speed at which a vehicle can negotiate a curve is dependent upon the radius of the curve, the

value of the superelevation and the permissible value of the coefficient of friction. The following formula

relates these factors: V2 = 127 R(e+f) ...(171) Where V= Speed in kilometres per hour R= Radius in

metres e = Value of superelevation, expressed as a fraction f = Coefficient of friction. The values

of/"recommended by AASTHO (Ref. 10) are given in Table 17-4. Table 17-4 Coefficient of lateral friction

recommended by AASTHO

Design speed K.P.H.

50

65

80

100

120

130

Maximum lateral friction

016

015

014

013

012

0-11

The Kenya/Indian Road Congress recommends a constant value of 0-15 (Ref. 11).

51

It is also possible to arrive at the speed on curve which drivers consider as a reasonable maximum. If

speed data of vehicles are collected at the curve, the 85th percentile speed could be used as the safe

speed for posting on the curve.


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(b) 17-2-10-3. Safe speeds at intersections

The safe speeds at intersections are governed by factors such as the sight distance available and the

type of traffic sign that is provided (STOP or GIVE WAY sign). The most common methods available for

determining the safe speeds prescribed by some of the U.S. bodies are: (i) National Safety Council

Method. (ii) American Automobile Association Method. (iii) American Association of State HighwayOfficials Method. (i)National Safety Council Method. The following figure represents the basis of the

method: Fig. 17-1. Basis of National Safety Council Method of Speed Zoning. A and B are two vehicles, A

travelling on the major or preferential street and B travelling on the side street. The view at the

intersection is restricted due to the presence of an obstruction. Point C represents the potential collision

point and CBA represents the visibility triangle. Since triangles CBA and DAE are similar, Da is taken as

equal to the safe stopping distance of vehicle A travelling at a speed V K.P.H. plus a clearance of 5 m The

braking distance is given by: Where d = braking distance in metres i; = speed in metres per second g =

acceleration due to gravity, m/sec2 f = coefficient of friction V = speed in K.P.H. If f is assumed as 0-53,

The safe stopping distance S is the braking distance plus the distance travelled in the perception

reaction time, t seconds.

52

The values of t for various values of V are given in Table 17-4. Table 17-4 Perception-reaction time for

different speeds

V (K.P.H.)

0

20

40

60

80

100

t (seconds)

0-76

0-80

0-95

115

1-55


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20 Where Va = Speed in K.P.H. of vehicle A. Assuming the vehicle length to be 7-3 m, the time required

for vehicle A to clear the collision point, The same time is needed for vehicle B to travel a distance of

Db5, since this vehicle should not get closer to the collision point than the clearance distance of 5 m.

Equating both, The above method is applicable to streets intersecting at any angle, provided the

measurements a and b are taken parallel to the paths of vehicles A and B respectively. (ii) American

Automobile Association Method. The same principles as above are applied here, with the change that f

is taken 0.50, the clearance distance is taken as 4-5 m and the perception reaction time uniformly taken

10 second. This gives: Assuming that Va is the legal speed limit, the speed of vehicle B can be calculated

on the premise that the distance from B to the collision point should be equal to the safe stopping

distance plus a clearance of 4-5 m. The above quadratic equation can be solved for Vb. (Hi) AASHO

method (Ref. 13): In third method the coefficient of friction is taken as 0-4 and the perception reaction

time is taken as 20 seconds. This gives:

53

Vb can be calculated from this quadratic equation. The use of the above methods can be illustrated by

the following example. Problem 17-1. Assume Va = 60 K.P.H., a = 15 m, b = 20 m. Calculate the speed

limit on minor street. Solution. By NSC Method,

54

6.2.11 Speed laws

Speed laws vary from country to country and even in a country they vary from State to State. In U.S.A.,

for example, the following categories of law exist: (i) Those which require that the driver should drive at

a speed which is safe and reasonable according to the existing conditions of the road, and the potential

hazards that may be present on the road. The rule under these laws is called the Basic Speed Rule. (ii)Those which prescribe that the driver should drive at a safe and reasonable speed, but in addition

provide that any vehicle speed in excess of a designated limit is deemed to be a violation of the basic

speed rule. If any question is raised, the burden of proof falls upon the driver to prove that he was not

travelling at an unsafe speed. The designated limit is called the prima facie speed limit. (iii) Those which

prescribe an absolute limit above which it is always illegal to drive and below which it is always legal to

drive irrespective of the conditions. (iv) Those which prescribe special speed limits in given zones,

indicated by signs.

6.2.12 General effect of speed limits

Though a large number of drivers disregard the speed limits, yet it cannot be denied that speed limitshave an overall salutory effect (Ref. 15). They reduce the accident rate and bring down the number of

those who drive at higher speeds. Special beneficiaries are the motor cyclists and pedal cyclists (Ref. 6).

Speed limit is, therefore, a powerful tool in traffic regulation.

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6.3 Regulation of Vehicles


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The regulation of vehicles broadly covers the aspects indicated below: (i) Vehicle Registration (ii)

Construction and equipment of vehicles. (Hi) Size, weight and loads of vehicles (iv) Lighting of vehicles.

(v) Inspection of vehicles. (vi) Control of transport vehicles. (vii) Insurance.

6.3.1 Vehicle Registration

Vehicle registration is a basic requirement and the data accumulated prov

transport engineering 333

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