Traffic Volume Study Essay Example

measure and understand the magnitude, composition, and time and route distribution of volume for each area under his jurisdiction.

Definitions

• 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.
• Rate of flow: The equivalent hourly rate at which ehicles pass over a given point or section of a lane or roadway during a time interval less than 1hr. usually 15 min.
• 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.
•  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 

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.

Objectives

The purposes of carrying out traffic volume count are designing, improving traffic system, planning, management etc.

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.

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.

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.
• 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.

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

Methodology

Methods for volume survey: There are two major methods of counting vehicle for volume survey. They are-

1. Manual Counting Method and
2. Automatic counting method.

Manual Counting Method

In this method, vehicles are counted manually. There are two methods of manual counting:

1. Direct Method and
2. 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:

1. Contact system based on pneumatic, mechanical, magnetic or piezo-electric method and
2. 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.

Data Collection

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.
2. Date: Data for volume study was collected on July 19, 2007. It was Wednesday and it was a weekday.
3. Time: Time of data collection for volume study: 9:25 am to 9:55 am.
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.
5. Observation: Classified Vehicle Counts.
6. Method: Direct Manual Method.
7. Duration: 0 minutes (Short Count)
8. Equipment: Hand counter, Tally sheet, Clip
   

board etc.

Conclusion

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.

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.

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.

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 the calculation of AADT.