Traffic Engineering Management

7/23/2019 Traffic Engineering Management

1/119


2/119

Traffic Engineering andManagement /[email protected]

i

Traffic Engineering Management

(BEG469TE)

(Elective II)

Year: 4 Semester

Teaching Schedule Hours/week

Examination Scheme Total marks Remarks

Final Internal Assessment

L T P Theory Practical Theory Practical

3 2 0 80 - 20 - 100

Course objectives :

The main objective of the course "Traffic Engineering Management" is to impart knowledge about

traffic management systematically and scientifically with the use of concept of engineering. Trafficmanagement as a burning issue and is of high importance for the developing cities, it should be

followed by the future traffic load analysis. Key topics of the course attempt to impart knowledge in

the following contemporary concepts:

Conceptual knowledge in traffic management system;

Issues, relative importance and methods of Transport Management;

This course may be good platform for the Graduate (Masters' degree) course in Traffic Engineering and

Management.

Course Contents:

1. Introduction 2 hrs.

1.1 Scope and significance of Traffic Engineering Management

1.2 Traffic planning and modeling using prototype

1.3 Traffic related problems in major cities

1.4 Transportation network and their characteristics

2. Urban Traffic Planning 3 hrs.

2.1 Introduction to urban traffic planning

2.2 Calculation of traffic volume

2.3 Travel demand forecasting

3 .Traffic Characte ristics 3 hrs.

3.1 Basic traffic characteristics - Speed, volume and concentration.

3.2Relationship between Flow, Speed and Concentration


3/119


ii

4. Traffic Me asurement And Analysis: 5 hrs.

4.1Volume Studies - Objectives, Methods;

4.2 Speed studies - Objectives: Definition of Spot Speed, time mean speed and space mean

speed;

4.3Methods of conducting speed studies;

5. Speed Studies: 5 hrs.


5.2Presentation of speed study data;

5.3Head ways and Gaps;

5.4Critical Gap;

5.5 Gap acceptance studies.

6. Highway Capacity And Leve l Of Service: 5 hrs.

6.1Basic definitions related to capacity

6.2 Level of service concept

6.3 Factors affecting capacity and level of service

6.4 Computation of capacity and level of service for two lane highways Multilane

highways and free ways.

7. Parking Studies And Analysis : 5 hrs.

7.1Types of parking facilities - on street parking and off street Parking facilities;7.2Parking studies and analysis.

8 Traffic Safety: 7 hrs.

8.1Accident studies and analysis;

8.2Causes of accidents - The Road, The vehicle, The road user and the Environment;

8.3Engineering, Enforcement and Education measures for the prevention of accidents.

9 Traffic Control And Regulation: 5 hrs.

9.1Traffic Signals - Design of Isolated Traffic Signal by Webster method,

9.2Warrants for signalisation, Signal Co-ordination methods, Simultaneous, Alternate,

Simple progressic and Flexible progression Systems.

10. Traffic And Environment: 3 hrs.

10.1 Detrimental effects of Traffic on Environment;

10.2 Air pollution; Noise Pollution;

10.3 Measures to curtail environmental degradation due to traffic.


4/119


iii

11. Traffic Management in Nepal 2 hrs.

11.1 Overview of existing system and future trend

11.2 National Transport Policy, Five Year Plans

11.3 Existing planning process

Tutorials:

1. A case study on traffic measurement and analysis

References

1. Traffic Engineering and Transportation Planning - L.R. Kadiyali, Khanna Publishers.

2. Traffic Engineering - Theory & Practice - Louis J. Pignataro, Prentice Hall Publication.

3. Principles of Highways Engineering and Traffic Analysis - Fred Mannering & Walter

P. Kilareski, John Wiley & 50ns Publication.

4. Transportation Engineering - An introduction - C. Jotin Khistry, Prentice Hall

Publication.

5. Fundamentals of Transportation Engineering - C.S.Papacostas, Prentice Hall India.

Question Pattern:

Chapter Marks allocated Remarks

1 4

2 4

3 4

4 10

5 10

6 10

7 10

8 10

9 10

10 4

11 4

Total 80

***Above mentioned marks can be with minor variations.


5/119


iv

Contents

CHAPTER ONE: INTRODUCTION ........ ........ ......... ....... ........ ........ ......... ....... ........ ........ ......... ....... ... 1

1.1Scope and significance of Traffic Engineering and Management .................................................. 1

1.2 Traffic planning and modeling using prototype............ ........ ........ ........ ........ ........ ......... ....... ........ 2

1.3 Traffic related problems in major cities ........ ........ ......... ....... ........ ........ ......... ....... ........ ........ ....... 3

1.4 Transportation network and their characteristics ..... ......... ........ ......... ...... ......... ........ ......... ...... ..... 6

CHAPTER TWO: URBAN TRAFFIC PLANNING ......... ........ ........ ....... ......... ........ ......... ...... ......... .... 8

2.1 Introduction to urban traffic planning........... ......... ........ ....... ........ ........ ......... ....... ........ ......... ...... 8

2.2 Calculation of traffic volume.................................................................................................... 10

CHAPTER THREE: TRAFFIC CHARACTERISTICS ......... ........ ........ ....... ......... ........ ........ ....... ....... 16

3.1 Basic traffic characteristics - Speed, volume and concentration................................................... 16

3.2Relationship between Flow, Speed and Concentration ................................................................ 17

CHAPTER FOUR: TRAFFIC MEASUREMENT AND ANALYSIS .................................................. 21

4.1 Volume Studies ....................................................................................................................... 21

4.2 Speed studies .......................................................................................................................... 26

4.3Methods of conducting speed studies; ........ ......... ........ ....... ........ ......... ........ ....... ........ ......... ....... 27

CHAPTER FIVE: SPEED STUDIES................................................................................................. 32

5.1Head ways and Gaps ................................................................................................................ 32

5.2 Uncontrolled Intersection ........ ........ ......... ....... ........ ........ ......... ....... ........ ........ ......... ....... ........ . 33

5.3 Gap acceptance studies ............................................................................................................ 37

CHAPTER SIX: HIGHWAY CAPACITY AND LEVEL OF SERVICE ...................................... .... .... 45

6.1Basic definitions related to capacity...... ........ ......... ........ ....... ........ ........ ......... ....... ........ ......... .... 45

6.2 Factors affecting capacity and LOS ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ .. 47

6.3 Level of Service concept .......................................................................................................... 49

6.3 Computation of capacity and level of service for two lane highways, multilane highways and

freeways....................................................................................................................................... 50

CHAPTER SEVEN: PARKING STUDIES AND ANALYSIS ............................................................ 70

7.1Types of parking facilities - on street parking and off street Parking facilities .... ........................... 70

7.2Parking studies and analysis ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ........ ...... 73

CHAPTER EIGHT: TRAFFIC SAFETY ......... ........ ........ ....... ......... ........ ........ ....... ......... ........ ........ .. 78


6/119


v

8.1Accident studies and analysis ........ ........ ......... ....... ........ ......... ........ ....... ........ ......... ........ ....... .... 78

8.2Causes of accidents - The Road, The vehicle, the road user and the Environment .... .... .... .... ......... 80

8.3 Accident studies, records and analysis ......... ........ ......... ....... ........ ........ ......... ...... ......... ........ ..... 81

8.3Engineering, Enforcement and Education measures for the prevention of accidents. ..................... 86

CHAPTER NINE: TRAFFIC CONTROL AND REGULATION......................................................... 90

9.1Warrants for traffic control signal system...... ........ ......... ........ ....... ........ ......... ........ ....... ........ ..... 90

9.2 Design Principles of Traffic Signal ................ ........ ........ ......... ........ ........ ....... ......... ........ ........ .. 90

9.3 Signal Co-ordination methods, Simultaneous, Alternate, Simple progression and Flexible

progression Systems...... .... .... ..................... .... ............................ .... ............................ .... ............... 99

CHAPTER TEN: TRAFFIC AND ENVIRONMENT ........ ........ ......... ....... ........ ........ ......... ....... ........106

10.1 Detrimental effects of Traffic on Environment.... ........ ........ ......... ....... ........ ........ ......... ....... ....106

10.2 Air pollution; Noise Pollution........... ........ ........ ....... ......... ........ ........ ....... ......... ........ ........ .....109

10.3 Measures to curtail environmental degradation due to traffic ...................................................112

REFERENCES................................................................................................................................113


7/119


1

CHAPTER ONE: INTRODUCTION

1.1 Scope and significance of Traffic Engineering and Management

Traffic engineering is one of the specialized areas of transportation engineering which is itself a branch of

civil engineering. It deals with traffic studies, analysis and engineering application for the improvement of

traffic performance on road.Institute of Traff ic Engineers (USA): Traffic Engineering is that phase ofengineering which deals with planning, geometric design and traffic operations of streets and highways,

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

achievement of safe, efficient and convenient movement of persons and goods.

Necessity:

It is relatively new branch of civil engineering.

It became necessary with the increase in traffic (number of vehicles).

Traffic congestion, parking problem, environmental degradation, traffic accidents, has created the

attention to the performance characteristics of highway transportation and continuous study and

developments for better geometric design, capacity, intersections, traffic regulations, signals,

signs, roadway marking, terminals, street lighting etc.

Has been recognized as an essential tool in the improvement of traffic operation

Objective of the Traffic Engineering

Basic objective is to achieve efficient, free, and rapid flow of traffic with minimum number of traffic

accidents. Traffic engineering includes a variety of engineering and management skills and the followings

are the main aspects:

Traffic characteristicsvehicles and road users

Traffic study and analysisspeed, volume, capacity, traffic pattern, OD,

Traffic flow characteristics, parking and accident studies

Traffic operation, control and regulationlaws and traffic regulatory

Measures, installation of traffic control devicessigns, signals and islands

Planning and analysisseparate phase for expressways, arterial roads,

Mass transit facilities, parking facilities etc. Designsgeometric design, parking facilities, intersections, terminals, lighting

Traffic administration and managementengineering, education and enforcement

Continual research

ROAD TRAFFIC MANAGEMENT: As urban populations expand and city roads become increasingly

congested, policy makers and planners need to review urban development and transport policies in order

to address future needs taking into account anticipated social and demographic changes.


8/119


2

Effective policy must meet multiple objectives:

Strike a balance between different modes of transport: pedestrians, bicycles, motorcycles, cars

and public transport

Provide security, safety and optimum service for transport system users

Maintain the mobility that drives economic development

Reduce urban pollution and congestion caused by motor vehicles

Alongside longer-term solutions such as upgrading public transport systems and introducing city center,

road toll systems, high-performance traffic management systems can be crucial to the success of a city

planning and transportation policy

Traffic Management Solutions include:

Improved road user safety:better traffic control for improved road safety and shorter response

times by emergency services

Quicker travel times in urban areas: smoother traffic flows and shorter public transport journeytimes

Less pollution: lower fuel consumption and less environmental impact

Widespread availability of road user information: accurate, reliable user information to

improve the travel experience

1.2 Tra ffic planning a nd modeling using prototype

As the number of traffic is increasing exponentially, traffic related problems has born. For the smooth and

effective traffic flow with minimizing traffic accidents and travel cost and maximizing the comfort andeasiness, traffic planning among the city has become inevitable. For the traffic planning, modeling using

prototype study is the best solution for the selection of best among the best alternatives.

Model concept

A model can be defined as a simplified representation of a part of real world-the system of interest-which

concentrates on certain elements considered for its analysis from a particular point of view. For the

analysis, any model made should be calibrated and validated to ascertain the realistic resemblance and the

same validated model is used for the further analysis.

Model calibration is the process by which the numerical values of the parameters of an assumed model

are determined. It is accomplished through the use of Statistical methods and based on experimental

knowledge that is observations, of the dependent and independent variables. These observations are

employed to estimate the numerical values of the model parameters that render the postulated model

capable of reproducing the experimental data. Several statistical goodness-of-fit tests, the one that best

describes the experimental data can then be selected. In this manner it is ensured that the selected model is

realistic. The term calibration refers to procedures that are used to adjust the values of a model's

parameters to make them consistent with observations.


9/119


3

Model validation refers to the testing of a calibrated model using empirical data than those used to

estimate the model in the first place. It means to predict a situation from the past and to compare this with

the actual situation in the present (back casting). This is how scientific theories are tested, modified, or

replaced.

Figure 1Methodological steps of model building process

1.3 Traffic related problems in major cities

Exponential growing of number of traffic within the limited fixed facilities like highway, interchange,

bridge etc is itself a great traffic related problem in the major city like Kathmandu. Followings are the

major traffic related problems:

Road space and Traffic Congestion:According to reports there are 180,000 (most of them being two

and three wheelers) vehicles registered at The Bagmati Transport Office at present. Considering the

narrow roads and the small area that the city is built in, these vehicles are too many for a city like

Kathmandu. The prevailing high degree of congestion, despite relatively low number of vehicles (private

car ownership rate is relatively low though there is relatively high number of vehicles registered, the most

of them being the two and three wheelers) is often attributed to the small proportion of urban space

devoted to roads. It is also revealed that the annoying causes of traffic jams in the streets of the city are

due to large number of motorbike riders. Traffic congestion is already an important constraint to urban

productivity and the vehicular air pollution is increasing and posing a serious health threat to urban

population.

Accidents: There has been an unprecedented trend in traffic accident in Kathmandu valley. While the

vehicles are increasing in geometric proportion, the roads are being constructed at a snail's pace.

Accidents are increasing in number and severity. Accidents occur more during working days when the

traffic is heavy. According to a report by the Traffic Engineering and Safety Unit at the Departments of

Roads, the frequency of accidents is at the peak at 4 pm followed by 8 am. Pedestrians are the ones who


10/119


4

are most at risk, followed by motorcycle riders. Accidents also occur when holidays are near and mostly

youngsters tend to drive under the influence of alcohol. Most accidents in the valley happen at

intersections. The places in Kathmandu that witness accidents frequently include Teenkune, Koteshwor,

Harihar Bhawan, Putali Sadak, Ring road and many other intersections, while nocturnal mishaps are more

frequent on the Ring Road, Kantipath and Naya Baneshwor because of over speeding.

The traffic condition: There is no doubt that the wide variety of traffic sharing the limited right of way is

a serious factor in congestion. Most road sections in Kathmandu city are not channelized for motor

vehicles, bicycles and pedestrians. The greater the pressure on road space, the more speeds of the slowest

moving vehicles tend to be reduced, and the potential of faster public, commercial and private vehicles are

wasted. Often pedestrians, market and parking activities intrude even the road space of major arteries. The

greater number of traffic accidents and lower overall average speed of the vehicles in the streets are

attributed to the large number of motorbikes and tempos.

Parking: It is one of the city's chronic problems, particularly in the Business Districts and other sites

where jobs and retail activities are concentrated. The limited road space is further reduced due to

encroachment of the road space by street shops, vehicles and bicycle parking. In particular, parking on the

sidewalks of the streets causes danger to pedestrians. In many cases, construction materials can be seen

placed at footpath and sometimes even on the roads thus forcing the pedestrians to walk on the roadway

which is primarily meant for the motor vehicles. This may cause a great deal of danger for the safety of

the pedestrians. Many buses have to be parked on the streets. Bus terminals have not been well planned

and cause a lot of transfer difficulties for the passengers.

Public transport: Public transport in Kathmandu city can be seen in general as a well-connected but

inadequate capacity is reflected in extreme overcrowding during long periods of peak hour traffic and it

takes a long time in reaching their destination. The development of public transport is often hindered by a

lack of capacity, low operating speed, and outdated equipment and management practices. As there is no

single bus terminus, finding the different places from where buses leave can sometimes be an experience

because there is a lack of information at public places. Also the seating arrangements in most of these

buses are such that you would hardly get to see the scene outside as you journey.

Pedestrians and cyclists: There is problem of movement by pedestrians and cyclists. Pedestrians (and

particularly the safety of pedestrians) are generally not accorded adequate priority by the city officials

responsible for planning and managing roads, as footpaths are inadequate and badly maintained.

Pedestrian crossings are placed in a long walking distance and many people simply don't cross the roads

using the overhead bridge. There are no any rules and regulations regarding punishment for those who

cross the road randomly. As a result walking and crossing streets in many places have become highly

dangerous. Conditions for cyclists are even worse than for pedestrians. Bicycle riding is increasingly


11/119


5

hazardous. As a result, this cheap and potentially very important mode of transport tends to be grossly

underutilized.

Road maintenance: Roads are inadequately maintained. Visual inspection and evaluation of road

network conditions show failures of the road pavement. A key factor contributing to this situation is the

lack of funding for the maintenance by the government. The situation is exacerbated by the absence of

computer based asset inventory and maintenance management systems. The available scarce resources are

allocated to meet the most pressing demands. In addition to managing existing roads more efficiently

additional capacity is needed by the construction of new roads.

Urban patterns: Physical patterns of cities also compound the difficulties. Central business districts are

typically not so clearly demarcated as in the developed world. The main activities centers are however

often concentrated in narrow streets prone to the intense congestion. High densities of intersections,

winding configurations and changing road widths reduce capacity further.

Road user education: It has not been very efficient and had lacked proper methodology and facilities.

The striking feature of the city traffic is the poor driving behavior. Driving standards are generally low. It

may be amazing to know that many of the drivers have no idea about the traffic signs and rules, which

indicates that our license issuing system is also extremely unscientific and impractical, and it is helping in

adding traffic accidents indirectly. It is reported that in Kathmandu valley the number of accidents are

higher than in the rest parts of Nepal and it can be said that the root cause of increasing traffic accidents is

the lack of traffic awareness among drivers and also pedestrians.

Traffic control measures: Effective road capacity of the city is further reduced by extensive uncontrolledparking of vehicles of all kinds and by ineffective signaling and other traffic control measures. Manual

control of junctions at peak hours is often required-land traffic signal timings are not appropriate. None of

all the existing traffic signals in the urban area are coordinated, most of them operating under two phase

fixed time control. Although there have been some successful experiments with junction channelization

recently in the city, the majority of the junctions have not been channelized and sometimes traffic island

itself is creating the traffic problem due to its inappropriate placement and bad design. Traffic signs and

markings are too much insufficient. Although some innovative pedestrian crossing facilities have been

implemented in the city, there is still a striking need for better provision of pedestrian crossing facilities to

give pedestrians safer ways to cross the road.

Remedial measures:

As mentioned earlier, with the very rapid growth in demand for transport, Kathmandu is facing serious

traffic problems. The immediate concern in the city is to maintain the existing levels of service of the road

system and personal mobility, whilst reducing the potential for road accidents. For this, traffic

management measures are to be utilized which typically will include junction improvements, one way

streets, segregation of two wheel vehicles with motor vehicle, channelization, markings, signaling,


12/119


6

selective road widening and provision of pedestrian facilities, continuous traffic awareness program

through the involvement of all the sectors of the society. But traffic management is the concern of the

number of policy and executive agencies. As a result there is pressing need for close coordination,

effective decision making machinery and enforcement, and clearly defined responsibilities because the

success or failure of traffic management measures largely depend on the institutional arrangements.

1.4 Tra nsportation network a nd their characteri stics

The transport system is represented by a network comprising of nodes and links that connect the nodes.

The network model is a simplified reproduction of the real network. The network is used to calculate the

travel times between points of origin and points of destination.The links of the network represent theroads. The nodes of the network are the intersections. Nodes in the model network are also used to mark

changes in road types and the sites, for example of bridge and other specific infra structure facilities.

The link may be:

Freeways:These roads provide largely uninterrupted

travel, often using partial or full access control, and

are designed for high speeds. Often freeways are

included in the next category, arterials. Arterials:

Arterials are major through roads that are expected

to carry large volumes of traffic. Arterials are often

divided into major and minor arterials, and rural and

urban arterials.

Collectors: Collectors (not to be confused with collector/distributor roads, which reduce weaving on

freeways), collect traffic from local roads, and distribute it to arterials. Traffic using a collector is usually

going to or coming from somewhere nearby.

Local roads: These roads have the lowest speed limit, and carry low volumes of traffic. In some areas,

these roads may be unpaved.

Link properties

Length

Travel speed

Capacity of link

Additional information about the link may be given

Type of road

Road width

Presence of bus lane, prohibition for certain vehicle etc

Banned turns

Type of junction Storage capacity for queues

Figure 2 Road Networks


13/119


7

Approximate equivalence with road classification in other countries is as follows: class I roads correspond

to expressways, class IIto arterial roads, class III-to collector roads and class IV-to local roads.

In Nepal the overall management of National Highways and Feeder Roads comes within the respons ibility of the

Department of Roads (DOR). These roads are collectively called Strategic Roads Network (SRN) roads. District

Roads and Urban Roads are managed by Department of Local Infrastructure Development and Agricultural Roads

(DOLIDAR). These roads are collectively called Local Roads Network (LRN) roads.


14/119


8

CHAPTER TWO: URBAN TRAFFIC PLANNING

2.1 Introduction to urban traffic planning

As the traffic on the existing road system in cities grows, congestion becomes a serious. Medium and long

term solution like widening roads, providing elevated fly-overs and constructing bypasses and urban

expressways are costly. Simple and inexpensive solutions can tide over the crisis for some time. Planning

and managing the urban traffic could be a package of short term measures to make the most productiveand cost-effective use of existing transportation facilities, services.

The fundamental approach in traffic management measures is to retain as much as possible existing

pattern of streets but to alter the pattern of traffic movement on these, so that the most efficient use is

made of the system. In doing so, minor alternations to traffic lanes, islands, curbs etc. are inevitable, and

are part of the management measures. The general aim is to reorient the traffic pattern on the existing

streets so that the conflict between vehicles and pedestrians is reduced.

Some of the well-known traffic management measures are:

Restrictions on turning movements

One-way streets Tidal-flow operations

Exclusive Bus-lanes

Closing side-streets.

Restrictions on turning movements

At a junction, the turning traffic includes left-turners and right-turners. Left-turning traffic does not

usually obstruct traffic flows through the junctions, but right-turning traffic can cause serious loss of

capacity. At times, right-turning traffic can lock the flow and bring the entire flow to a halt. One way of

dealing with heavy right-turning traffic is to incorporate a separate right-turning phase in the signal

scheme which result in a long signal cycle. Another solution is to ban the turning movement altogether.

Prohibition of right-turning movement can be established only if the existing street system is capable of

accommodating an alternative routing.

One-way Streets

As the name itself implies, one-way streets are those where traffic movement is permitted in only one

direction. As a traffic management measures intended to improve traffic flow, increase the capacity and

reduce the delays, one-way streets are known to yield beneficial results. They afford the most immediate

and the least expensive method of alleviating the traffic conditions in a busy area. In combination with

other methods such as banned turning movements, installation of signals and restrictions on loading and

waiting, the one-way street system is able to achieve great improvement in traffic conditions of congested

areas.

Whenever a system of one-way streets is introduced, it is imperative that proper signs should be put up to

foster safe and efficient traffic. 'No entry' signs are needed at all terminal points of the one-way streets. At

the entrances and exits of all intersections within the scheme, 'one-way' and/or 'two-way' traffic signs

should be displayed. It may be necessary to put up 'No left turn' and 'No right turn' signs at some

junctions.


15/119


9

Advantages

Reduction in the points of

conflict

Increase capacity

Increase speed

Facilitating the operation

of a progressive signal

system

Improve in parking system

Elimination of dazzle and

head on collision

Tidal-flow operations

One of the familiar characteristics of traffic flow on any street leading to the city center is the imbalance

in directional distribution of traffic during the peak hours. For instance, the morning peak results in a

heavy preponderance of flow towards the city center, whereas the evening peak brings in heavier flow

away from the city center. In either case, the street space provided for the opposing traffic will be found to

be in excess. This phenomenon is commonly termed as "tidal flow". One method of dealing with this

problem is to allot more than half the lanes for one direction during the peak hours. This system is known

as "tidal flow operation", or "reverse flow operation".

Closing Side-streets

Figure 3Four legged intersection and conflict points

Figure 4 Tidal flow operation


16/119


10

A main street may have a number of side-streets where the traffic may be very light. In such situations, it

may be possible to close some of these side-streets without affecting adversely the traffic, and yet reap a

number of benefits.

Exclusive Bus Lanes

A recent innovation in traffic management practice in some of the Cities is to reserve a lane of the

carriageway exclusively for but traffic. This is possibly only in situations where the carriageway is of

adequate width and a lane can be easily spared for the buses. This implies that there should be at least 3

lanes in each direction. For reasons of convenience of alighting and embarking passengers at the curb, the

exclusive lane has to be adjacent to the curb.

2.2 Calculation of traffic volume

Traffic volume is the number of the vehicles crossing a section of road per unit time at any selected

period. Traffic volume is used as a quantity measure of traffic flow. A complete traffic volume study

includes the classified volume study by recording the volume of various movements and the distribution

on different lanes per unit time.The volume of different type is usually converted into Passenger Car Unit

(PCU).

NRS 2070

Table 1PUC factors (Source: NRS 2070)

SN Vehicle type Equivalency factor

1 Bicycle, motorcycle 0.5

2 Car, auto rickshaw, SUV, light van andpick up

1.0

3 Light (mini), truck, tractor, rickshaw 1.5

4 Truck, bus, minibus, tractor with trailer 3.0

5 Non-motorized carts 6.0

The objectives and uses of traffic volume studies are:

Traffic volume study is generally accepted as true measure of the relative importance of roads and

in deciding the priority for improvement and expansion.

Traffic volume study is used in planning, traffic operation and control of existing facilities and

also for planning and designing the new facilities.

Traffic volume study is used in the analysis of traffic patterns and trends

Classified traffic volume study is useful in structural design of pavements, in geometric design

and in computing roadway capacity. Volume distribution study is used in planning one way

streets and other regulatory measures.

Turning movement study is used in the design of intersections, in planning signal timings,

channelization and other control devices.


17/119


11

Pedestrian traffic volume study is used for planning sidewalks, cross walks, subways and

pedestrian signals.

Types of Traffic Volume:

Average annual traffic flow: expressed in vehicle per year.

Annual Average Daily Traffic (AADT):expressed in vehicles per day. It is (1/365) th of the

total annual traffic flow. Total number of vehicles passing the site in a year is divided by 365

days. All vehicles are converted into passenger car unit.

Average Daily traffic (ADT): If the flow is not measured for all the 365 days, but only for few

days (less than one year) the average flow is known as Average Daily Traffic (ADT).

Average Annual Weekday Traffic (AAWT): is the average 24 hour traffic volume occurring on

weekdays over a full year. Average weekday traffic: is an average 24 hour traffic volume occurring on weekdays for some

period less than one year, such as one month or one season.

Hourly flow: vehicle/hour, peak hour volume.

Variation in traffic flow and accuracy of counts

Traffic counts carried out over a very short time period can produce large errors because traffic flows

often have large hourly, daily, weekly, monthly and seasonal variations. These variations are described in

the following sections.

Hourly variations

An example of hourly traffic variation throughout one day is shown below. In this example major traffic

flow occurs between 05 and 21 hours. In practice traffic counts will usually be carried out for 12, 16 or 24

hour time periods. Typically, in tropical countries, a 12 hour traffic count (example from 6:00 to 18:00)

will measure approximately 80 % of the days traffic whereas a 16 hour count (example from 6: 00 to

22:00) will measure over 90 percent.

In order to obtain estimates of 24 hour flows from counts of less than 24 hours duration, it is necessary to

scale up the counts of shorter duration according to the ratio of flow obtained in 24 hours and the flows

measured in the shorter counting period.

Scale factor (converting a partial days count into a full days traffic count)


18/119


12

Figure 5 Hourly Variation

For reasons of statistical analysis, HCM (1997) suggests using 15 minutes for most operational and design

analyses. The relationship between hourly volume and the maximum rate of flow within the hour is

defined as the peak hour factor.

For 15 minutes periodsthe maximum value of the PHF 1.0 which occurs when the volume in each 15

minutes period is equal, the minimum value is 0.25 which occurs when the entirely hourly volume occurs

in one 15 minute interval.

Daily and weekly variation

The day to day traffic flows tend to vary more than the week to week flows over the year. Hence large

errors can be associated with estimating average daily traffic flows (and hence annual traffic flows) fromtraffic counts of only a few days duration, or which exclude the weekends. Thus there is a rapid increase

in the accuracy of the survey as the duration of the counting period increases up to one week. For counts

longer than one week, the increase in accuracy is less pronounced.

Figure 6 Daily Variation

Monthly and seasonal variation

Traffic flows will rarely be the same throughout the year and will usually vary from month to month and

from season to season. The seasonal variation can be quite large and is caused by many factors. For

0

200

400

600

800

1000

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

Hourly variation of traffic flow

0

2000

4000

6000

8000

SAT SUN MON TUES WED THURS FRI

Daily variation of traffic volume

Series1


19/119


13

example, an increased traffic flow usually occurs at a harvest time, and a reduced traffic flow is likely to

occur in a wet season.

To reduce error in the estimated annual traffic data caused by seasonal traffic variations, it is desirable to

repeat the classified traffic count at different times of the year. A series of weekly traffic counts repeated

at intervals throughout the year will provide a much better estimate of the annual traffic volume than a

continuous traffic count of the same duration.

An example of seasonal variation is shown below. For one week traffic count carried out each month. A

seasonal factor (SF) of unity indicates average flow. A seasonal factor greater than unity, indicates a

higher proportion of traffic than the average. It can be seen that the traffic is lower than average in

December, January, February, July and August. The variation in flow for different classes of vehicle may

not be the same and this will be revealed in the classified traffic survey.

Figure 7Seasonal variation

Problem 2.2: The following counts were taken on an intersection

approach during the morning peak hour. Determine (a.) the hourly

volume, (b) the peak rate of flow within the hour and (c) the peak hour

factor.

Example 2.3: The following traffic count data were taken from a

permanent detector location.

Month

2 .No. of weekdays in

Month(days)

3.Total days in

Month(days)

4.Total Monthly

volume(vehs)

5.Total weekday

volume(vehs)

Jan 22 31 200000 170000

Feb 20 28 210000 171000

Mar 22 31 215000 185000

Apr 22 30 205000 180000

May 21 31 195000 172000

0

500

1000

1500

Jan Feb March Apr May Jun Jul Aug Sep Oct Nov Dec

Seasonal variation of traffic flow

Series1

1.501.31

0.920.80 0.83

1.07 1.131.25

0.96

0.71

0.84

1.31

0.00

0.50

1.00

1.50

2.00

Jan Feb March Apr May Jun Jul Aug Sep Oct Nov Dec

seasonal factors

Time Period Volume

8:00-8:15 AM 150

8:15-8:30 AM 155

8:30-8:45 AM 1658:45-9:00 AM 160


20/119


14

Jun 22 30 193000 168000

Jul 23 31 180000 160000

Aug 21 31 175000 150000

Sep 22 30 189000 175000

Oct 22 31 198000 178000

Nov 21 30 205000 182000

Dec 22 31 200000 176000

From this data, determine (a) the AADT, (b) the ADT for each month, (c) the AAWT, and (d) the AWT

for each month, from this information, what can be discerned about the character of the facility and the

demand it serves?


21/119

Traffic Engineering andManagement /[email protected] 15

Example 2.1: Following table shows the classified manual vehicle count of a 14th

February 2015 for three hour at Pepsikola - Manohara - Thimi - Hanumante - Sallaghari

Road. Determine the AADT in term of PCU with given data: the three hour traffic figures out about 20% of the total traffic at that day, Lane factor for FR 0.6.

Result of Classified Manual Vehicle Count

Start Date: Location: Peps ikola ,

Road Link: Peps ikolaManohara Note:Direction a: Pepsikola - Manohara Station:

Name of Road: Pepsikola - Manohara - Thimi - Hanumante - Sallaghari Road Direction b:Manohara-Pepsikola Station No.:

Seasonal Variation Factor for the Month of Feburary: 1.31 Surveyed By:

Date: 14th Feburary

2015

DateStart Time

(Hrs)

Volume of Vehicles

Truck BusCar

Motor

Cycle

Utility

VehicleTractor

Three

WheelerRickshaw

Four Wheel

Drive/Jeep,Van

Power

TillerTotal

Heavy Light Mini Micro

A b a b a b a b a b a b a b a b a b a b a b a b a b

14th Feburary,

2015

12:30-1:30 2 9 13 13 12 17 23 194 203 8 7 1 6 7 247 268 515

1:30-2:30 6 2 14 6 10 12 1 32 30 183 188 9 9 1 1 1 1 9 10 1 1 266 261 527

2:30-3:30 4 5 37 52 41 57 98


22/119

Traffic Engineering andManagement /snlkhyaju@gmail .com 16

CHAPTER THREE: TRAFFIC CHARACTERISTICS

3.1 Basic traffi c characteristics - Speed volume and concentration.

Traffic flow is very complex. It requires more than causal observation while driving on a freeway to discover

that as traffic flow increases, there is generally a corresponding decrease in speed. Speed also decreases, when

vehicles tend to bunch together for one reason or another. Such analysis includes transverse and longitudinaldistribution of vehicles, distribution over time. Thus the provision of the theoretical consistent quantitative

technique by which relevant dimensions of vehicular traffic can be modeled, forms the basis of traffic

analysis.

Traffic flow is a stochastic process, with random variations in vehicles and driver characteristics and their

interactions. The theory of traffic flow can be defined as a mathematical study of the movement of vehicles

over road network. The subject is a mathematical approach to define, characterize and describe different

aspects of vehicular traffic. The development of the topics has taken inspiration from the various field of

knowledge such as, statistics, applied mathematics, psychology and operation research etc.

Approaches to understanding traffic flow:Three main approaches to the understanding and quantification

of traffic flow. The first being the macroscopic based on the analogies as fluid flow. This approach is most

appropriate for studying steady state of flow and hence best describes efficiency of the system. The second is

microscopic approach that consider the response of each individual vehicle in a disaggregate manner. In this

case, individual driver-vehicle combination is examined, and therefore is extensively used in highway safety

work. The third is the human-factor approach, which basically tries to define the mechanism by which an

individual driver and the vehicle locate oneself with reference to another vehicle and the highway guidance

system.

Vehicle flow on transportation facilities may be classified into two categories:

Uninterrupted flow:it occurs on the facilities that have no fixed elements, such as traffic signals, external to

traffic stream , that cause interruption to traffic flow.

Interrupted flow:it occurs on transportation facilities that have fixed elements causing periodic interruptions

to traffic flow. Such elements are traffic signals, stop signs, and other types of controls. These devices cause

traffic to stop periodically.

It should be noted that uninterrupted and interrupted traffic flow are terms to describe the facility and not the

quality of flow.

Speed (v)

It is defined as the rate of motion, as distance per unit time, generally km/h. or m/sec. There is a wide

distribution of individual speed in a traffic stream, an average speed is considered. If travel time t1, t2, t3.

tn, are observed from nvehicles traveling a segment of length L , the average travel speed is:

n

i

i

n

i

i

s

t

nL

nt

Lv

11


23/119


Example3.1: Three vehicles are traversing a 1.5 km segment of a highway and following observation is made:

What is the average travel speed of the vehicle?

Vehicle A: 1.2 min. (72 sec.)

Vehicle B: 1.5 min. (90 sec.)

Vehicle C: 1.7 min. (102 sec.)

The average travel speed calculated is referred as the space mean speed (vs). It is called space mean speed

because the use of average travel time essentially weights the average according to length of time each vehicle

spends in space.

Another way of defining average speed of traffic stream is by finding the time mean speed (vt). This is the

arithmetic mean of the measured speeds of all vehicles passing, say, a fixed roadside point during a given

interval of time, in which case, the individual speeds are known as spotspeeds.

n

v

v

n

i

i

t

1

Where,vi,is the spot speed, and nis the number of vehicles observed.

Volume (q)

Volume and rate of flow are two different measures. Volumeis the actual number of vehicles observed or

predicted to be passing a point during a given time interval. The rate of flow represents the number of vehicles

passing a point during a time interval less than one hour, but expressed as an equivalent hourly rate.

Density or concentration

It is defined as the number of vehicles occupying a given length of lane or roadway, averaged over time

usually expressed as vehicles per km. direct measurement of density can be obtained through aerial

photography, but more commonly it is calculated from the equation if speed and rate of flow are known,:

kvq * Where, q= rate of flow veh. /hr)

v = average travel speed, m/sec

k = average density (veh/km)

3.2Rel ationship between Flow Speed and Concentration

q= rate of flow veh. /hr

v = average travel speed, m/sec

k = average density (veh/km)

Then, =

Now Density, k = Hence q=k*v


24/119


Analysis of Speed, Flow, and Density Relationship

It has been assumed that a linear relationship exists between the speed of traffic on an uninterrupted traffic

lane and the traffic density, as shown in figure below. Mathematically it is represented by:

BkAv

Where,vis the mean speed of the vehicle.

kis the average density of vehicles veh/km.

Aand Bare empirically determined parameters

We know,

B

vv

B

A

B

vAvkvq

BkAkkvq2

2

)(

At almost zero density, the free mean speed equals to A, and at almost zero speed, the jam density equals A/B.

The maximum flow occurs at about half the mean free speed and is equal to A2/4B.

The theoretical relationship between flow and density on a highway lane, represented by a parabola. The flow

increases from zero to its maximum value, the corresponding density of this flow is optimum density (ko).

From this point onward to the right, the flow decreases as the density increases. At the jam density ( kj), the

flow is almost zero.

Density, veh/km

Meanspeed,

km/h

Density, veh/km

Flow,veh/h

Flow, veh/h

Meanspeed,

km/h

A

A/B

A2

/4B

V=A-Bk

A/2B

A/B

A

A/2

a) b) c)

Speed -Flow-Density curves

A2/4B

Figure 8Speed-Flow-Density curves


25/119


Greenshields Model:in 1935, Greenshields developed a model based on empirical studies.

.....(ii)....................}{or,

)(or,)(Then,

)........(i..........)(QThen,

or,*QthatknowWe

ionconcentrat

ionconcentratjamming

conditionsflowfreeforspeedmeanspace

speedmeanspace

)(

2

2

s

sf

j

js

sjssfsf

sj

sf

sfs

j

sf

sf

s

s

j

sf

s

j

sf

sfs

vv

KKvQ

vKvvQvv

Q

K

vvv

KK

vKv

v

QKKv

K

K

v

v

KK

vvv

Differentiating the equation (i) with respect to concentration, we can get the value of concentration

corresponding to the maximum flow.

i).......(ii....................2Then,

02

jK

K

jK

ksfvsfv

dK

dQ

To obtain the speed corresponding to the maximum flow, the equation (ii) is differentiated with respect to vs.

......(iv)....................2

or,

02

sfvsv

sfv

svjKjK

sdv

dQ

(v)....................42

*2

maxK*Qmaximumfor)(max:Therefore

jKsfvjKsfv

imumQforsvimumQ

Relation between time mean spee d and space mean speed:

Considering a stream of traffic with a total flow of Q, consisting of subsidiary stream with flows q1, q2, q3

.qcand speeds v1, v2, v3, vc.

c

i

iqqqqQ1

c321 q..........................

For the subsidiary stream with flow q1and speed v1:

Average time headway = 1/q1


26/119


Distance traveled in that time = v1/q1

The density of the stream in space (the number of vehicles per unit length at any instant is given by:

ctv

qk

i

ii ......3,2,1,

The total concentration:

c

i ikK1

The time mean speed s defined as:

c

i

iit

Q

vqv

1

The space mean speed is defined as:

c

i

iis

K

vkv

1

Relationship between space mean speed and time mean speed

s

sst

vvv

2

Example 3.2: Assuming a linear speed-density relationship, the mean free speed is observed to be 85 km/hnear zero density, and at the corresponding jam density is 140veh/km. Assume that, the average length of

vehicles is 6m.

Write down the speed-density and flow-density equations.

Draw the v-k, v-qand q-kdiagrams indicating critical values.

Compute speed and density corresponding to flow of 1000 veh/h.

Example 3.3: Speed observations from a radar speed meter have been taken, giving the speeds of the

subsidiary streams composing the flow along with the volume of traffic of each subsidiary stream. The

readings are as under.

Speed range 2-5 6-9 10-13 14-17 18-21 22-25 26-29 30-33 34-37 38-41 42-45 46-49 50-53 54-57 58-61

Volume (qi) 1 4 0 7 20 44 80 82 79 49 36 26 9 10 3

Calculate: a) time mean speed b) space mean speed c) variance about space mean speed

Example 3.4:The speed density relationship of traffic on a section of a freeway lane was estimated to be

Vs= 18.2 ln(220/k)

a) What is the maximum flow, speed, and density at this flow?

b) What is the jam density?

Example 3.5: Determine the maximum flow for the free flow speed of 80 kmph. The aerial photograph shows

that average center to center spacing of two vehicle during jam (i.e. velocity is zero) is found to be 6.5 m.


27/119


CHAPTER FOUR: TRAFFIC MEASUREMENT AND ANALYS IS

4.1 Volume Studies

Definition

Traffic volume is the number of the vehicles crossing a section of road per unit time at any selected period.

Traffic volume is used as a quantity measure of traffic flow. Unit used for this is vehicle/day; vehicle/hour etc.A complete traffic volume may include the classified volume study by recording the volume of various types

of vehicle, distribution by direction and lane and turning movements.

The volume of different type is usually converted into Passenger Car Unit (PCU).

NRS 2070

SN Vehicle type Equivalency factor

1 Bicycle, motorcycle 0.5

2 Car, auto rickshaw, SUV, light van and

pick up

1.0

3 Light (mini), truck, tractor, rickshaw 1.5

4 Truck, bus, minibus, tractor with trailer 3.0

5 Non-motorized carts 6.0

Objectives:

It is the true measure of relative importance of roads, which is important for improvement andexpansion.

Traffic volume is used in planning, traffic operation/control of existing facilities and for planning new

facilities. Classified volume is used for structural design of pavements.

It is used to analyze traffic pattern and trends.

It is used for design intersections, signal timings, canalizations, and other control devices. For the determination of one-way street or other regulatory measures.

Pedestrian traffic volume is uses for planning and design of sidewalks, cross walks, subways, andpedestrian signals.

Hourly traffic volume varies considerably during a day. Peak hour is much higher than average hourlyvolume. Daily traffic varies in a week and also with season.

Types of traf f ic counts:

Short term counts:

For determining traffic flow in peak hours.

To measure saturation flow at signalized intersection

Count for full day

To determine hourly fluctuation of flow

Used intersection counts

Count for full week:

To determine hourly and daily fluctuation of flow

For traffic survey in urban highways.

Continuous count:

To determine fluctuation daily, weekly, seasonal and yearly flow.


28/119


To determine annual traffic growth rate

Very commonly used in developed countries at selected sections.

Methods of traf f ic counts:

Manual count

Combined Manual and mechanical counter

Automatic devices

Photographic Method.

Moving observer method

Manual Count:

The prescribed record sheet is provided for manual count. Vehicles are counted by the method of five-dash

system.

Date: Road class ification: Klometrage /mileage

Direction:

Vehicle type

Hour

Car, Jeep,

Van

Bus Micro

bus

Truck Three-

wheeler

Motor

bike

Cycle

8-9

9-11

11-12

It is more desirable to record traffic in each direction of travel separately. The data can be summarized for

each hour

of day.

Advantages of manual method:

Vehicle classification, type and occupants

Record of turning and straight going vehicle

Directional breakdown

Check of automatic count Data easy to analyze

Suitable for short and non-continuous count. Pedestrian count can also be done.

Enable to record unusual conditions

Figure 9Manual Traffic count


29/119


Disadvantages:

Costly

Continuous counting is not feasible.

Number of team member depends on the number of lane, total volume, complexity of area .

Equipment and tools:

Watch, pencils, erasers, blank field data sheets and a clipboard

Mechanical tally counters and electronic count boards can also be used which can be directlydownloaded to computers.

Manual count at intersections:

Field data sheet can be modified to suit the particular requirements of any intersection. Traffic enumerators

needed to be posted on each arm of the intersection. The count of traffic on each arm should be broken down

into three categories- left turning, right turning and straight ahead traffic.

Combined Manual and Mechanical Method

An example of a combination of manual and mechanical method is the multiple pen recorders. The chart

moves continuously at the speed of a clock. Different pens record the occurrence of different events on the

chart. Particular pen may record specific type of vehicle. Advantage of this type is:

Classification and count is done simultaneously

Time headway can be determined

Automatic device

The automatic devices consist of equipment for detecting the passage or presence of and another for recording

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

record chart.

Sensors (detectors):

1) Pneumatic tube (road tube): flexible tube with one end sealed is clamped to the road surface at right angles

to the pavement. Other end of the tube is connected to a diaphragm actuated switch. When an axle of the

vehicle crosses the tube a volume of air gets displaced thus creating a pressure which instantaneously closes

the electric contact through the switch. Two such contacts result in one count for the two axle vehicle. They

are cheap but it is difficult to fix on gravel surface and they are likely to be damaged by tractors and are easily

pilfered by vandals. They cannot detect vehicles by lane.

Figure 10 Combined Mechanical and Manual Method


30/119


2) Electric contact: A pair of steel strip is contained in a rubber pad which is buried beneath the road surface.

By the load of the vehicle, steel strips come into contact with each other and cause the electric current to flow.

3) Co-axial cable: A co-axial cable is clamped across the road surface, with the capability of generating

signals with the passage of axles. These signals actuate a transistorized counter. They are more reliable then

above-mentioned devices.

4) Photo-electric: A source of light is installed on the one side of the road, which emits a beam of light across

the road. At the other end a photo-cell which can distinguish the light beam and its absence, is fixed. By the

passage of vehicle, photo-cell records the obstruction to the light beam. There may be error due to passage of

vehicle at the same time in different lane.

5) Radar: A Radar (Doppler Effect) may detect the vehicle moving at a speed. When a moving object

approaches or recedes from the sources of signals, the frequency of the signal received back from the moving

object will be different from the frequency of the signal emitted by the source. This difference in two

frequencies causes the detection of the moving object. The initial cost is high but it is reliable and accurate.

6) Infra-red: Infrared sensors can detect the heat radiated from a vehicle or can react to the reflection from the

vehicle of infra-red radiation emitted by the sensors.

7) Magnetic: the disturbance caused by the passage of vehicle to the magnetic field, is taken as the basis of

sensing. Magnetic field is provided by a wire coil, which is buried beneath the road surface.

Recording Me chanism:

The signals generated by the automatic sensors can be recorded by the various methods:

1) Counting register: it is simply an accumulating counter, which indicates the number of the vehicle.

Readings must be taken before and after the counting period.

2) Printed output: this device prints the accumulated totals at regular interval of time on a roll of paper.

3) Electronic system: they are modern system, which can record data directly on floppies or other magnetic

disk.

Video Photographic method:

It gives the permanent record of volume counts. Its analysis can be done at office by replaying the cassette.

Presentation and analysis of traffic volume data

Data collected during the traffic volume study are sorted out and are presented in any of the following forms

depending upon requirements:

Average Annual Daily Traffic (AADT):it is 1/365th

of the total annual traffic flow. It is expressed in terms

of PCU and used for determining importance and future development of the road.

Trend Chart:it shows the volume trends over the period of years. By extrapolating the trend we can estimate

the future volume prediction.

Variation Chart:for the presentation of hourly, daily, weekly, seasonal variations such charts are prepared.

They are useful to determine facilities and regulations for the peak hour requirements.

Traffic flow at intersection shown by thick lines:for the intersection design and control measures.


31/119


Traffic Flow Maps:along the routes of the road

network, are useful for the graphical presentation

for the volume study. Traffic volume distribution on

the road network can easily be noticed.

HourlyTrafficVolume,

%o

fADT

0 20 40 60 80 100

Numbers of hours in one year

with traffic volume

exceeding that shown

30thh

ighesthour

30th

Highest Hourly Volume (design hourly

volume): It is the hourly volume that will be

exceeded only 29 times in a year and all other

hourly volumes of the year will be less than this

value. For the economic point of view, the highest

hourly volume is not accepted for designing of the

facilities. And the annual average hourly volume

will not be sufficient during considerable period of

year. So for designing traffic facilities, the

congestion only 29 hours in the year is permissible.

Thus the 30th

highest hourly volume is generally

taken as the hourl desi n volume.

1050

450

600

100

700

300

Traffic flow at intersection

0

500

1000

1500

2000

2500

3000

3500

4000

0 4 8 12 16 20 24 28 32 36 40 44 48 52 56 60 64 68 72 76 80 84 88 92 96

Totalnumberoftrafficflow

Number of 15 min duration

15 minutes total traffic flow

Traffic flow map

Figure 11Graphical Representation of Traffic data


32/119


4.2 Speed studies

Definition of terms

Speed is a factor influencing traffic flow on existing roads. Speed studies are essential for:

Traffic operation like sign location and timings, establishing speed zones etc.

Geometric design of elements like curvatures, super elevation, stopping sight distance etc.

Spot speed:it is an instantaneous speed of a vehicle at a specific location.

Running speed: It is the average speed of vehicles along a given section of road excluding delays at

controlled intersection.

Running speed = length of course/running time = length/ (journey time- delay time)

It is useful for assessing traffic capacity of roads.

Journey speed: it is average speed of vehicles along a route including all delays, but excluding all voluntary

stoppages. It is useful in urban areas for measuring time adequacy an existing road network, for assessing the

efficiency of the improvement measures.

Journey speed = length of route/ total journey time including delays

Average speed:average spot speed of several vehicles passing a specific section is termed as average speed.

Application:

For the traffic control and regulation, in geometric design, accident studies, studying traffic capacityetc.

Effect of traffic flow constraints like bridge and intersection

Spot speed is affected by physical of road like pavement width, curve, sight distance and grade.

There are two types of average speed: Space mean speed and time mean speed.

Space mean speed:Average speed of vehicles over a certain length of road at a given time. This is obtained

from the observed time of the vehicles over a relatively long stretch of the road.

Space mean speed (kmph),

n

ii

s

t

dnV

1

6.3

n=Number of individual vehicle observation; d- Length of the road section. ti- observed travel time in sec

for the ith vehicle to travel dm.

Time mean speed: it represents speed distribution of vehicles at a point on the roadway and it is the average

of instantaneous speed of observed vehicles at the spot.

n

V

V

n

ii

t

1

Vtis time mean speed (km/h); Viobserved instantaneous speed

of the ith vehicle kmph; nno of vehicles observed.


33/119


Spot Speed study:

Uses:

Geometric design of roads;

Regulation and control of traffic operation; Anglicizing the causes of accidents;

Before and after study of improvement projects;

Determining the problems of congestion in the road section;

Capacity study.


Methods of Spot speed measurement:

Methods available for the measuring spot speed can be grouped as follows:

Those who require observation of time taken be the vehicle to cover a known distance;

Direct timing procedure;

Enoscope

Pressure contact tube

Radar speed-meter which automatically records the instantaneous speed;

Photographic method

General consideration for the site selection foe spot speed measurement:

Location selection should be according to the specific purpose;

Minimum influence to the traffic flow and their speed by the survey team and equipment;

Generally straight, level and open section should be selected.

Recommended base length:

Average speed of traffic stream, km/h Base length

Less than 40 27

40-65 54

Greater than 65 81

a) Direct timing procedure for the spot speed determination:

Simple method

Two reference points are marked on the pavement at a suitable distance apart and an observer startsand stops an accurate stopwatch as a vehicle crosses these two marks.

From the known distance and measured time intervals spot speed is calculated;

Large effects may occur due to the parallax effect; Reaction of individual observer may affect the result.

One observer stands at the first reference point and gives signal to the observer standing at lastreference point (with stopwatch).

Figure 12 Stopwatch spot speed study layout


34/119


b) Enoscope

It is a simple device consisting of L-shaped mirror box, open at both ends. It has a mirror set fixed at 45

degree to the arms of the instrument as in figure.

50 m

Light for night

Figure 13: Enoscope method

c) Pressure contact tubes

In this method detectors are used to indicate the time of entering and leaving the base length by the vehicle.

d) Inductive loop detector

Two wire loops are inserted in the pavement at known distance apart and radio frequency at 85-115 kHz is fed

to the circuit tuned to avoid electric interferences. When the vehicle passes over the loop it causes shift of

phase in frequency thus recording the vehicle presence.

e) Radar speed meter:This automatic device works on the Doppler principle that the speed of a moving

body is proportional to the change in frequency between the radio wave transmitted to the moving body and

the radio wave received back. It directly measures speed.

Figure 14Pressure contact tubes

Fi ure 15Tra ic Police usin Radar Gun Meter


35/119


f) Photographic and video camera method

Time-lapse camera photography has been used to determine the speed of the vehicles. In this method,

photographs are taken at fixed intervals of time on a special camera. By projecting the film on the screen, the

passage of any vehicle can be traced with reference to time.

Video camera also can be used to measure the speed of the vehicle.

Presentation and analysis of spot speed data

Spot speed depends on factors like volume and composition of traffic, geometric layout, and condition of the

road, environmental conditions, human and vehicle characteristics etc. Careful consideration is necessary

while presenting the data.

Tabular presentation: grouping of spot speeds into speed cases to facilitate esay computation.

Graphical presentation: (Histogram and cumulative frequency curves)

Modal speed:peak of the frequency curve. (mode of the distribution)

Median Speed:50th

percentile speed

98th

percentile speed: below this speed 98% of vehicles move, and it is taken as design speed for the

geometric design.

85th

percentile speed: 85% of the vehicles move below this speed. It is used to establish upper speed limit

for traffic management. It is taken as limit of safe speed in the road.

15th

percentile speed:15% of vehicles move below this speed. It is used for determining minimum speed

limit for major highways.

Arithmetic mean or average spot speed: Summation of all variable speed divided by the number of

observations.

Spot speed observation table (say the stretch of the road section L=50 m):

Observation

number1 2 3 4 5 ..

Observed time 3.52 3.45 2.85 3.25 2.65 .. .

Speed (km/h) 51.14 52.2 63.2 55.4 67.9 .

Grouping of data and presentation:

Large amount of data could be presented by arranging them in a frequency table . First data should be

grouped into suitable class interval. Size of class interval:

N

Rangei

10log22.31 Where, iis the class interval, Nis the number of observations.

Paramete rs of Distribution

The frequency table, histogram and the cumulative frequency curve give only the rough idea of the

distribution and their inherent characteristics. An accurate idea about distribution can be expressed from the

parameters of distributions .


36/119


Histogram: vertical axis: percentage

frequency; horizontal axis: class-limits.

The cumulative percentage frequency

diagram:

The Pace: Another Measure of Central

Tendency The pace is a traffic engineering

measure not commonly used for other

statistical analyses. It is defined as the 10

kmph increment in speed in which the

highest percentage of drivers is observed. It

is also found graphically using the

frequency distribution curve. The solution

recognizes that the area under the

frequency distribution curve between any

two speeds approximates the percentage of

vehicles traveling between those two

speeds, where the total area under the curve

is 100%.

The pace is found as follows: A 10 kmph

template is scaled from the axis. Keepingthis template horizontal, place an end on

the side of the curve a move slowly along

the curve. When the right side of the

template intersects the right side of the curve, the pace located. This procedure identifies the 10 kmph

increment that the peak of the curve; this contains the most area and, the highest percentage of vehicles.

Percent Vehicles within the Pace. The pace itself is a measure of the center of the distribution. The

percentage of vehicles traveling within the pace speeds is a measure of both central tendency and dispersion.

The smaller the percentage of vehicles traveling within the pace, the greater the degree of dispersion in the

distribution. The percent of vehicles within the pace is found graphically using both the frequency distribution

and cumulative frequency distribution curves. The pace speeds were determined previously from the

frequency distribution curves. Lines from these speeds are dropped vertically to the cumulative frequency

distribution curve. The percentage of vehicles traveling at or below each of these speeds can then be

determined from the vertical axis of the cumulative frequency distribution curve

Example 4.1: Three cars with speed 20kmph, 40kmph and 60kmph travelling length D. Determine the space

mean speed and time mean speed.

Example 4.2:Twenty five spot speed observations were taken and were as under (km/h):

50, 40, 60, 54, 45, 31, 72, 58, 43, 52, 46, 56, 43, 65, 33, 69, 34, 51, 47, 41, 62, 43, 55, 40, 49

Calculate: a) time mean speed, b) space mean speed, and c) verify the relation between them.

30.00 40.00 50.00 60.00

speed, km/h

0.00

5.00

10.00

15.00

20.00

%Frequency

LLR Smoother

Figure 16Presentation of Speed data


37/119


Example 4.3: Consider the following spot speed data, collected from a freeway site operating under free-flow

conditions:

a) Plot the frequency and cumulative frequency curves for these data.

b) Find and identify on the curves: medium speed, modal speed, pace, percent vehicles in pace.

c) Compute the mean and standard deviation of the speed distribution.

Speed Group (kmph) Number of vehicles observed (N)

15-20 0

20-25 3

25-30 6

30-35 1835-40 45

40-45 48

45-50 18

50-55 12

55-60 4

60-65 3

65-70 0


38/119


CHAPTER FIVE: SPEED STUDIES

5.1Head ways and Gaps

Spacing and headway are two additional characteristics of traffic streams. Spacing (s) is defined as the

distance between successive vehicles in a traffic stream as measured from front bumper to front bumper.

Headway (h)is the corresponding time between successive vehicles as they pass a point on a roadway. Bothspacing and headway are related to speed, flow rate and density.

hourvehh

q

v

msh

kmvehk

/;sec,)(headwayaverage

3600

sec,m/sec),(speedaverage

),(spacingaverage

/;m(s),spacingaverage

1000

Spacing of vehicles in a traffic lane can generally be observed from aerial photographs. Headway of the

vehicles can be measured using stopwatch observations as vehicles pass a point on a lane.

20 40 60 80

Speed, km/h

Minimumspacing,m

10

20

30

40

60

80

Figure: Variation of Min spacing and headway with speed

0

Minheadway,sec

100

0

1

2

3

Headway,Sec

Spacin

g,m

Spacing (m) or

headway (sec)

L, m

Clearance (m)

gap (sec)

Figure: Clearance-gap and Spacing-headway

Figure 17 Clearance-gap and Spacing- Headway


39/119


Lane occupancy (R): is a measure used in freeway surveillance. If one could measure the lengths of vehicles

on a given roadway section and compute the ratio.

D

LR

i

sectionwayroadoflength

vehiclesoflengthsofsum

Rcould be divided by the average length of a vehicle to give an estimate of density (k).

Lane occupancy (LO)can also be described as the ratio of the time that vehicles are present at a detection

station in a traffic lane compared to the time of sampling.

L

C

L= length of the vehicle

C= distance between the loops of detector

Loop detector

sv

CLt

T

tLO

0

0

n timeobservatiototal

occupiedisdetectorvehicletimetotal

Density can be calculated by the formula:

CL

LOk

1000*

Lane clearance (c) and Gap (g)are related to the spacing parameter and headway. These four measurements

are shown in figure below. The difference between spacing and clearance is obviously the average length of a

vehicle in m. Similarly the difference between headway and gap is the time equivalence of average length of a

vehicle (L/v):

5.2 Uncontrolled Intersection

An intersection is a road junction where two or more roads either meet or cross at grade. This intersection

includes the areas needed for all modes of travel: pedestrian, bicycle, motor vehicle, and transit. Thus, the

intersection includes not only the pavement area, but typically the adjacent sidewalks and pedestrian curb cut

Where, gis the gap, m;

L is the mean length of vehicle, m;

cis the mean clearance, m;

his the mean headway, sec;

vis the mean speed, m/sec


40/119


ramps. All the road junctions designated for the vehicles to turn to different directions to reach their desired

destinations. Traffic intersections are complex locations on any highway. This is because vehicles moving in

different direction want to occupy same space at the same time. In addition, the pedestrians also seek same

space for crossing. Drivers have to make split second decision at an intersection by considering his route,

intersection geometry, speed and direction of other vehicles etc. A small error in judgment can cause severe

accidents. It causes delay and it depends on type, geometry, and type of control. Overall traffic flow depends

on the performance of the intersections. It also affects the capacity of the road. Therefore, both from the

accident perspective and the capacity perspective, the study of intersections are very important by the traffic

engineers.

Categories of Intersection

Intersection design can vary widely in terms of size, shape, number of travel lanes, and number of turn lanes.

Basically, there are four types of intersections, determined by the number of road segments and priority usage.

Priority Intersection:Occur where one of the intersecting roads is given definite priority over the other. The

minor road will usually be controlled by some form of sign marking, such as stop or yield sign; thus ensuring

that priority vehicles travailing on the main street will incur virtually no delay.

Space sharing intersection:Are intended to permit fully equally priority and to permit continuous movement

for all intersecting vehicle flows; example would be rotaries and other weaving areas.

Time Sharing Intersection:Are those at which alternative flows are given the right of way at different point

in time. This type of intersection is controlled by traffic signal or by police officer.

Uncontrolled intersection:are the most common type of intersection usually occurs where the intersecting

roads are relatively equal importance and found in areas where there is not much traffic shown in figure. At

uncontrolled intersection the arrival rate and individuals drivers generally determine the manner of operation,while the resulting performance characteristics are derived from joint consideration of flow conditions and

driver judgment and behavior patterns. In simplest terms, an intersection, one flow of traffic seeks gaps in

the opposing flow of traffic.

At priority intersections, since one flow is given priority over the right of way it is clear that the secondary or

minor flow is usually the one seeking gaps. By contrast at uncontrolled intersection, each flow must seek

gaps in the other opposing flow. When flows are very light, which is the case on most urban and rural roads

large gaps exist in the flows and thus few situation arise when vehicles arrive at uncontrolled intersection less

than 10 second apart or at interval close enough to cause conflicts. However when vehicles arrive at

uncontrolled intersection only a few second apart potential conflicts exist and driver must judge their relative

time relationships and adjusts accordingly.

Generally one or both vehicles most adjust their speeds i.e. delayed somewhat with the closer vehicle most

often taking the right of way; in a sense, of course, the earlier arriving vehicle has priority and in this

instance when two vehicles arrive simultaneous, the rule of the road usually indicate priority for the driver

on the right. The possibility of judgmental in these, informal priority situation for uncontrolled intersection is

obvious. At an uncontrolled intersection, service discipline is typically controlled by signs (stop or yield signs)

using two rules two way stop controlled intersection (TWSC) and all way stop controlled intersection

(AWSC).


41/119


Two-Way Stop-Controlled Intersection

Researchers rely on many specific definitions to describe

the performance of traffic operation systems. The clear understanding of such terminology is an important

element is studying two-way stop-controlled (TWSC) traffic operation system characteristics; defined as: One

of the uncontrolled intersections with stop control on the minor street shown in Fig. 4.

Characteristics of TWSC Intersections

At TWSC intersections, the stop-controlled approaches are referred to as the minor street approaches; the

intersection approaches that are not controlled by stop signs are referred to as the major street approaches. A

three-leg intersection is considered to be a standard type of TWSC intersection if the single minor street

approach is controlled by a stop sign. Three-leg intersections where two of the three approaches are controlled

by stop signs are a special form of uncontrolled intersection control.

Figure 20Traffic flow stream in two way stop controlled intersection source

Figure 19Two way stop controlled intersection

Figure 18uncontrolled intersection


42/119


Flow at TWSC Intersections

TWSC intersections assign the right-of-way among conflicting traffic streams according to the following

hierarchy:

Rank 1 - The major street through and right-turning movements are the highest-priority movements at a

TWSC intersection. This movements shown Fig. 4 are 2, 3, 5, 6, 15 and 16.

Rank 2 - Vehicles turning left from the major street onto the minor street yield only to conflicting Major

Street through and right-turning vehicles. All other conflicting movements yield to these major street left-

turning movements. The movements on this rank are 1, 4, 13, 14, 9 and 12.

Rank 3 -Minor Street through vehicles yield to all conflicting major street through, right-turning, and left-

turning movements. The movements on this rank are 8 and 11.

Rank 4 -Minor Street left-turning vehicles yield to all conflicting major street through, right-turning, and left-

turning vehicles and to all conflicting Minor Street through and right-turning vehicles. The movements on this

rank are 7 and 10.

All-Way-Stop-Controlled Intersection (AWSC)

AWSC Intersection are mostly used approaching from all d

Date post:	14-Feb-2018
Category:	Documents
Upload:	-
View:	221 times
Download:	0 times

Traffic Engineering Management

Documents