traffic engineering management
TRANSCRIPT
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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
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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.
5.1Methods of conducting speed studies;
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.
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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.
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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
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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
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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.
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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.
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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
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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
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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,
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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
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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.
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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.
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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
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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.
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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)
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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
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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
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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?
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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
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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
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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
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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
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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
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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.
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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.
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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
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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
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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.
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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
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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.
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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.
4.3Methods of conducting speed studies;
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
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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
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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 .
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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
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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
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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
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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
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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).
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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
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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