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Traffic Volume Study

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Traffic Volume Study


List of Content

1. Introduction
2. Scope and Objectives
3. Methodology
4. Data collection
5. Data analysis
6. Conclusion



Introduction

1.1. Traffic Survey:
Traffic engineers and planners need information about traffic. They need information to design and manage road and traffic system. They use the information for planning and designing traffic facilities, selecting geometric standards, economic analysis and determination of priorities. They use this to justify warrant of traffic control devices such as signs, traffic signals, pavement markings, school and pedestrian crossings. The also use this information to study the effectiveness of introduced schemes, diagnosing given situations and finding appropriate solutions, forecasting the effects of projected strategies, calibrating and validating traffic models.
Transportation system is a dynamic system. Information about traffic must be regularly updated to keep pace with ever-changing transportation system. Data must be collected and analyzed systematically to get representative information.
Traffic surveys are the means of obtaining information about traffic. This is a systematic way of collecting data to be used for various traffic engineering purposes.

1.1.a. Main purposes of traffic survey:
The main purposes of traffic survey are: traffic monitoring, traffic control and management, traffic enforcement, traffic forecasting, model calibration and validating etc.

1.1.b. Parts of traffic studies:
Traffic studies include:
 Inventory of road traffic physical features
 Traffic stream characteristics- volume, speed, density, occupancy studies etc.
 Capacity studies of streets and intersections
 System usage studies- Travel time and delay, O-D survey
 Travel demand- home interview survey
 Road users cost- Value of travel time, vehicle operating cost
 Parking supply & demand studies
 Axle load survey
 Mass transit performance and usage studies
 Traffic accidents studies
 Environmental impact studies of transport
1.2. Traffic Volume Study:
Traffic data are needed in research, planning, designing and regulation phases of traffic engineering and are also used in established priorities and schedules of traffic improvements. The traffic engineer must acquire general knowledge of traffic volume characteristics in order to measure and understand the magnitude, composition, and time and route distribution of volume for each area under his jurisdiction.

1.3. Definitions:
1.3.a. Volume/flow: The total number of vehicles that pass over a given point or section of a lane or roadway during a given time interval. It is the actual number of vehicle observed or predicted to passing a point during a given interval.
1.3.b. Rate of flow: The equivalent hourly rate at which vehicles pass over a given point or section of a lane or roadway during a time interval less than 1hr. usually 15 min.
1.3.c. Average Daily Traffic (ADT): The volume during a given time period divided by the number of days in that time period and expressed in terms of vpd.
1.3.d. Average Annual Daily Traffic (AADT): It is the total yearly volume divided by the number of days in a year and expressed in terms of vpd.

Chapter Two
Scope and Objectives

2.1. Scope Of Traffic Volume Studies:
The traffic volume count study is carried out to get following useful information:
 Magnitudes, classifications and the time and directional split of vehicular flows. Magnitude is represented by volume of traffic. Vehicles are classified into some predefined classes based on vehicle size and capacity. In a two-way road, vehicles moving towards two directions are counted separately to get the proportion. Time and directional split is useful to identify tidal flow.
 Proportions of vehicles in traffic stream. Proportion of vehicles indicates whether public or private transport dominates the traffic system. It also indicates the choice of road users.
 Hourly, daily, yearly and seasonal variation of vehicular flows. These variations are needed to establish expansion factors for future use. Using expansion factors, AADT can be calculated from short count.
 Flow fluctuation on different approaches at a junction or different parts of a road network system.

2.2. Objectives:
The purposes of carrying out traffic volume count are designing, improving traffic system, planning, management etc.
2.2.a. Design purposes:
 Structural and geometric design of pavements, bridge, and other highway facilities. Structural design is based on repetition of wheel load on the pavement in entire design life. AADT is needed with traffic growth rate to compute design wheel repetition. Geometric design is based on peak hour volume to avoid congestion.
 Intersection design including minimum turning path, channelization, flaring, traffic control devices viz. traffic signs, markings, signals based on approach volume and turning proportions.
 Pedestrian volume study is useful for designing side walks, pedestrian crossing etc.
2.2.b. Improvement purposes:
 To allocate limited maintenance budget rationally, it is important to know the traffic volume carried by a particular roadway section in order to decide the importance of the road and fixing its relative priority.
 In order to improve the roadway operating condition, it is important to know the traffic volume.
 To examine the existing operating/service condition of a roadway section.
 To check the need (warrant) traffic control devices.
 To determine the type of improvement measure need to be taken.
 To measure the effectiveness of a traffic control measure
2.2.c. Planning Purposes:
 Accurate information on the amount of traffic on the roads is vital for the planning of both road maintenance and improvement policies
 Traffic volume network analysis helps in deciding/planning if there is need for
 Improvement
 Expansion in terms of construction missing links, by-pass, alternative road etc.
2.2.d. Dynamic Traffic Management Purposes:
 Up to date and continuous flow/congestion information is essential for optimizing
 Traffic signal design and thereby improving junction performance
 Network productivity by providing information to the road user
2.2.e. Other Purposes:
 Estimation of highway usage
 Measurement of current demand of a facility
 Estimation of trends
 Economic feasibility evaluation
 Computation of accident rates- accidents/100M vehicle-miles


Chapter Three
Methodology

3.1. Methods for volume survey:
There are two major methods of counting vehicle for volume survey. They are- i)Manual Counting Method and ii) Automatic counting method.
3.1.a. Manual Counting Method: In this method, vehicles are counted manually. There are two methods of manual counting: i)Direct Method and ii)Indirect Method.
 Direct Method: Data is counted by using hand tally and manual counters/enumerators.
 Advantages: By this method traffic volume as well as vehicle classification and turning proportions can be obtained. Data can be used immediately after collection.
 Disadvantages: This method is not practicable for long duration count and when flow is high. Error is common especially when volume is high. Count cannot be cross checked. Count cannot be done in bad weather.
 Indirect Method: In this method, data is collected using video camera. Video is captured for long time and data is collected later by rewinding.
 Advantages: Besides traffic volume, several traffic parameters can be obtained from recorded film. Data can be cross checked and quality can be ensured. This method is applicable when volume is high. It is suitable for non-lane based traffic operation.
 Disadvantages: A suitable elevated place is required for filming operation. Data cannot be used immediately after collection. Data must be manually transcripted of recorded film. This process is time consuming and tedious. Because of limitation of capacity of film, it is not suitable for long duration counts. Quality of video recorded on film is dependent on intensity of light and this method is not suitable in overcast days.

3.1.b. Automatic counting method:
In this method, vehicles are counted automatically without any human involvement. There are two techniques of automatic counting: a) Contact system based on pneumatic, mechanical, magnetic or piezo-electric method and b) Contactless system based on electrical/optical, ultrasound/infrared radar, micro wave, CCTV/video image processing method etc.
 Advantages: This method is suitable for long duration or continuous count. It is used as permanent counting station. It does not need manpower and is free from human error. Data is obtained in usable format. It is less expensive as manpower is not needed. Count is not affected by bad weather condition.
 Disadvantages: It requires strict lane discipline. Non motorized vehicles are hard to detect by this method. Detailed classification of vehicle is not possible. Accuracy is less than manual method. Installation cost is high.

3.2. Counting periods:
Vehicles can be counted for any duration. Duration of count depends on the objective of data collection. For traffic control and management or operational studies short duration count at peak period is conducted. For planning and design purpose, long duration count is conducted.

Chapter Four
Data Collection
4.1. Location:
Location of the spot for traffic volume survey was chosen to be Mirpur Road near Science Laboratory intersection. Vehicles towards Russel Square were counted.

4.2. Date:
Data for volume study was collected on July 19, 2007. It was Wednesday and it was a weekday.
4.3. Time:
Time of data collection for volume study: 9:25 am to 9:55 am.
4.4. Weather Condition:
It was a hot humid day. Sky was partly cloudy. At the time of data collection it was drizzling for a while.
4.5. Observation:
Classified Vehicle Counts.
4.6. Method:
Direct Manual Method.
4.7. Duration:
30 minutes (Short Count)
4.8. Equipment:
Hand counter, Tally sheet, Clip board etc.
4.9. Number of Enumerators:
Six.

Chapter Six
Data Analysis
6.1. Volume/Flow (30 minutes):
GROUP1 GROUP2 GROUP3 GROUP4 GROUP5 GROUP6 TOTAL
LIGHT VEHICLE 331 396 518 845 626 558 3274
BUS 105 100 113 142 128 116 704
AUTO RICKSHAW 96 118 185 292 211 136 1038
MOTOR CYCLE 67 34 70 88 79 65 403
TRUCK 1 1 4 0 0 0 6
SMALL PUBLIC TR. 0 3 0 0 0 0 3
PCE 706.8 764 995.5 1477.6 1154.3 989.3 6087.5

6.2. Rate of Flow:
GROUP1 GROUP2 GROUP3 GROUP4 GROUP5 GROUP6 TOTAL
09:00-10:00 10:00-11:00 11:00-12:00 12:00-13:00 13:00-14:00 14:00-15:00
LIGHT VEHICLE 662 792 1036 1690 1252 1116 6548
BUS 210 200 226 284 256 232 1408
AUTO RICKSHAW 192 236 370 584 422 272 2076
MOTOR CYCLE 134 68 140 176 158 130 806
TRUCK 2 2 8 0 0 0 12
SMALL PUBLIC TR. 0 6 0 0 0 0 6
PCE/hr 1413.6 1528 1991 2955.2 2308.6 1978.6 12175 Average=2029

6.3. Vehicle Composition:
6.3.a.

6.3.b.

6.3.c.

6.3.d.

6.3.e.

6.3.f.

6.3.g.



6.4. Directional Distribution:
Direction Flow-rate
PCU/hr Percent
Towards Russel Square (North-North-West) 1644.2 41%
Towards Science Lab(South-South-East) 2414.13333 59%






6.5. Flow fluctuation:

time 09:00-10:00 10:00-11:00 11:00-12:00 12:00-13:00 13:00-14:00 14:00-15:00 total
PCE/hr 1413.6 1528 1991 2955.2 2308.6 1978.6 12175 average=2029




6.6. Annual Average Daily Traffic (AADT):
GROUP1 GROUP2 GROUP3 GROUP4 GROUP5 GROUP6 TOTAL
09:00-10:00 10:00-11:00 11:00-12:00 12:00-13:00 13:00-14:00 14:00-15:00
Hourly Expansion Factors 18.8 17.11 18.52 18.71 16.71 14.84
Daily Expansion Factors 7.012 7.012 7.012 7.012 7.012 7.012
Monthly Expansion Factors 0.578 0.578 0.578 0.578 0.578 0.578
AADT 15387 15137 21349 32013 22335 17000 Average 20537

Chapter Seven
Conclusion
7.1. Discussion on vehicle composition:
Vehicle composition shows that sixty percent of total traffic was light vehicles. Only thirteen percent was buses. The reason for high proportion of light vehicle is the proximity of the location to residential area of high income group people. The light vehicles were not highly occupied. But buses were almost fully occupied. It can be assumed that, more people were travelling by bus.

7.2. Discussion on directional distribution:
59 percent of traffic flow was towards Science Lab which indicates tidal flow towards south-east. It was morning rush hour. So flow was higher towards the city center. Only 41 percent of traffic was flowing towards north-west. If another vehicle count was done in evening rush hour, opposite scenario might be seen.

7.3. Discussion on flow fluctuation:
To draw flow fluctuation curve, it was assumed that volume for six continuous hours were counted, although all vehicles were counted within one hour. Each group counted vehicles for 30 minutes. Flow rate was calculated from that short count data and plotted. The flow fluctuation curve shows a peak at 12:00-13:00 hrs.
7.4. Discussion on Annual Average Daily Traffic (AADT):
AADT was calculated using expansion factors. These expansion factors established based on data collected in the United States. These factors were not calibrated for Dhaka city. So, they will not give actual AADT. Weekdays and weekends are different in hour country. So, the actual daily expansion factors will be much different from what is used. Monthly expansion factors will also be different because of difference in seasons and climate in the same month. The weather condition was not considered in calculating AADT. But, in a city like Dhaka, where water logging is a common phenomenon during heavy downpour, traffic volume should be significantly reduced in an overcast day. So, a weather factor should be introduced in calculation of AADT.

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