Traffic Engineering Management (BEG469TE) (Elective II) L T P Theory Practical Theory Practical

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Traffic Engineering and Management /[email protected]

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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. Traffic management 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 Characteristics 3 hrs.

3.1 Basic traffic characteristics - Speed, volume and concentration. 3.2Relationship between Flow, Speed and Concentration

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4. Traffic Measureme nt 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 Level 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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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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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 Traffic Engineers (USA): ―Traffic Engineering is that phase of engineering 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 characteristics—vehicles and road users

 Traffic study and analysis—speed, volume, capacity, traffic pattern, OD,

 Traffic flow characteristics, parking and accident studies

 Traffic operation, control and regulation—laws and traffic regulatory

 Measures, installation of traffic control devices—signs, signals and islands

 Planning and analysis—separate phase for expressways, arterial roads,

 Mass transit facilities, parking facilities etc.

 Designs—geometric design, parking facilities, intersections, terminals, lighting

 Traffic administration and management—engineering, 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 journey times

 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 Traffic planning and 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 and easiness, 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 uncontrolled parking 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 Transportation network and their characteristics

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 the roads. 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 II –to 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 responsibility 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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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 productive and 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 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

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 day’s 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 day’s count into a full day’s 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 periods—the 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) from traffic 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 1.50 1.31 0.92 0.80 0.83 1.07 1.13 1.25 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 165 8:45-9:00 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 tha t day, Lane factor for FR 0.6.

Result of Classified Manual Vehicle Count

Start Date: Location: Pepsikola ,

Road Link: Pepsikola – Manohara 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

Date Start Time (Hrs) Volume of Vehicles Truck Bus Car Motor Cycle Utility Vehicle Tractor Three Wheeler

Rickshaw Four Wheel Drive/Jeep,Van

Power Tiller

Total Heavy Light Mini Micro

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16 CHAPTER THREE: TRAFFIC CHARACTERISTICS

3.1 Basic traffic 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 longitudinal distribution 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 n vehicles traveling a segment of length L, the average travel speed is:

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17

Example 3.1: 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 ―spot” speeds.

n

v

n i i t





1

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

Volume (q)

Volume and rate of flow are two different measures. Volume is 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,:

k

v

q



*

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

v = average travel speed, m/sec k = average density (veh/km)

3.2Relationship between Flow, Speed and Concentration

q = rate of flow veh. /hr

v = average travel speed, m/sec k = average density (veh/km)

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18

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:

Bk

A

v





Where, v is the mean speed of the vehicle.

k is the average density of vehicles veh/km. A and B are empirically determined parameters We know,

B

v

B

A

B

v

A

v

kv

q

Bk

Ak

kv

q

2 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 M e a n s p e e d , k m /h Density, veh/km F lo w , v e h /h Flow, veh/h M e a n s p e e d , k m /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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19

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

...(ii) ... ... } { or, ) ( or, ) ( Then, ) ...(i ... ) ( Q Then, or, * Q that know We ion concentrat ion concentrat jamming conditions flow free for speed mean space speed mean space ) ( 2 2 s sf j j s s j s sf sf s j sf sf s j sf sf s s j sf s j sf sf s v v K K v Q v K v v Qv v Q K v v v K K v K v v Q K K v K K v v K K v v v                

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

i) ...(ii ... ... 2 Then, 0 2 j K K j K k sf v sf v dK dQ    

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

...(iv)

...

2 or,

0

2 sf

v

s

v

sf

v

s

v

j

K

j

K

s

dv

dQ







(v)

...

4

2 *

2 max

K

*

Q

maximum

for

)

(max

:

Therefore

j

K

sf

v

j

K

sf

v

imumQ

for

s

v

imum

Q



Relation between time mean speed and space mean speed:

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

….qc and speeds v1, v2, v3, ……vc.









c i i

q

Q

1 c 3 2 1

...

q

For the subsidiary stream with flow q1 and speed v1:

Average time headway = 1/q1

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20

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:

c

t

v

q

k

i i i



,



1 ,

2 ,

3 ...

The total concentration: 



c

i

k

i

K

1

The time mean speed s defined as:

   c i i i t Q v q v 1

The space mean speed is defined as: __

 c i i i s K v k v 1

Relationship between space mean speed and time mean speed

s s s t

v

2







Example 3.2: Assuming a linear speed-density relationship, the mean free speed is observed to be 85 km/h near 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-q and q-k diagrams 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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21 CHAPTER FOUR: TRAFFIC MEASUREMENT AND ANALYSIS

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 and expansion.

 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, and pedestrian signals.



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

.

Types of traffic 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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22

 To determine annual traffic growth rate

 Very commonly used in developed countries at selected sections. Methods of traffic 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 classification: 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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23

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 directly downloaded 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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24

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 the n 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 Mechanism:

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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25

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.

H o u rl y T ra ff ic V o lu m e , % o f A D T 0 20 40 60 80 100 Numbers of hours in one year

with traffic volume exceeding that shown

3 0 th h ig h e s t h o u r

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 highe st 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 hourly design 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

T

ot

al

n

u

m

b

e

r

of

t

raf

fi

c

fl

ow

Number of 15 min duration

15 minutes total traffic flow

Traffic flow map

Figure 11Graphical Representation of Traffic data

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26 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 capacity etc.

 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 i i s

t

dn

V

1

6 .

3

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

for the i th vehicle to travel d m.

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

n

i

t





1

Vt is time mean speed (km/h); Vi observed instantaneous speed

of the i th vehicle kmph; n no of vehicles observed.

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27

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 starts and 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 last reference point (with stopwatch).

Figure 12 Stopwatch spot speed study layout