TRAFFIC VOLUME STUDY 2010

INTRODUCTION:

Traffic Volume is the number of vehicles crossing a section of road per unit time at any selected period. Traffic volume is used as a quantity measure of flow, the commonly used units are vehicles per day and vehicles per hour.

OBJECTIVES & NEED OF STUDY:

One of the fundamental measures of traffic on a road is the volume of traffic using the road in a given interval of time. It is also termed as flow and it is expressed in vehicles per hour or vehicle per day. When the traffic is composed of a number of vehicles, it is the normal practice to convert the flow into equivalent Passenger-Car Unit (PCU), by using certain equivalency factors. The flow is then expressed as PCUs per hour or PCUs per day.

Knowing the flow characteristics one can easily determine whether a particular section of the road is handling traffic much above or below its capacity. If a traffic is heavy, the road suffers from congestion with consequent loss in journey speeds. lower the speeds causes ecomonicloss to the community due to time lost by the occupants of the vehicles and the higer operational cost of vehicles.Congesion also lead to traffic hazards. There for traffic volume data are require to draw up schemes for improvement of road network and also to allocate the scare economic resources most advantageously.

If a traffic flow data are available over the past number of years, the rate at which

traffic flow has increased in the past can be easily determined. Extrapolating the past trend into the future ,a reasonable indication of the future rate of growth of traffic is made possible.

If a average annual flow and the length of the highway are known, the annual vehicle kms of travel can easily be computed. Road pavement design pertaining to numbers of commercial vehicles using a road. The maintenance needs of a highway is often based on the traffic using the road.

Traffic regulatory and control systems are designed on the basis of accurate vehicle floe data. The design signal and road junction are possible only if, among other things, the vehicle flow data are available.

METHODS FOR COUNTING TRAFFIC VOLUME:(1) Mechanical counters(2) Manual counts

(1) Mechanical counters:These may be either fixed (permanent) type or portable type. The mechanical counter can automatically record the total number of vehicles crossing a section of the road in a desired period. The working may be by the effect of impulses or stimuli caused by traffic movement on a pneumatic hose placed across the roadway or by using any other of sensor.

TRAFFIC VOLUME STUDY 2010

Traffic count is recorded by electrically operated counters and recorders capable of recording the impulses. The impulses caused by vehicles of light weight may not be enough in some cases to actuate. The main advantages of mechanical counter is that it can work throughout the day and night for the desired period, recording the total hourly volume, which may not be practicable in manual counting. The main drawback of the mechanical counter is that it is not possible to get the traffic volumes of various classes of traffic in the steram and the details of turning movements.

(2)Manual counts:This method employs a field team to record traffic volume on the prescribed record sheets. By this method it is possible to obtain data which can not be collected by mechanical counters, such as vehicle classification, turning movements and counts where the loading condition or number of occupants are required. But it is not practicable to have manual count for all the 24 hours of the day .Hence it is necessary to resort to statically sampling techniques in order to cut down the manual hours involved in talking complete counts, First the fluctuation of traffic volume during the hours of day and the daily variations are observed. Then by selecting typical short count period, the traffic volume study is made by manual counting. Then by statistical analysis the peak hourly traffic volumes as well as the average daily traffic volumes are calculated. This method is very commonly adopted due to the specific advantages over other methods.

PRESENTATION OF TRAFFIC VOLUME DATA:

The data collected during the traffic volume studies are sorted out and are presented in any of the following forms depending upon the requirements.(a) Annual average daily traffic (AADT or ADT) of the total traffic as well as classified

traffic are calculated. This helps in deciding the relative importance of a route and in phasing the road development programme. In order to convert the different vehicle classes to one class such as passenger car, conversion factors known as passenger Car units(PCU) are used.

(b) Trend charts showing volume trends over period of years are prepared. These data are useful for planning future expansion, design and regulation.

(c) Variation charts showing hourly, daily and seasonal variations are also prepared .These help in deciding the facilities and regulation needed during peak traffic periods.

(d) Traffic flow maps along the routes,(the thickness of the lines representing the traffic volume to any desired scales),are drawn. These helps to find the traffic volume distribution at a glance.

(e) Volume flow diagram at intersection at either drawn to a certain scale or indicating traffic volume . Thus showing the detais of crossing and turning traffic.These data are needed for intersection design.

(f) Thirties highest hourly volume or the design hourly volume is found from the plot between hourly volume and the number of hours in an year that the traffic volume is exceeded.The 30th highest hourly volume is the hourly volume that will be exceeded only 29 times in a year and all other hourly volumes of the year will be lessthan this volume.the annual average hourly volume (AAHV) FOUND FROM aadt will not be

TRAFFIC VOLUME STUDY 2010

sufficient during considerable perioad of an year.The high facilities designed with capacity for 30th highest hourly traffic volume in the assumed year is found to be satisfactory from both facility and economic considerations.There will be congestion only during 29 hours in the year.thus the thirtieth highest hourly volume is generally taken as the hourly volume for design.Thus the thirtieth highest houly volume is generally taken as the houly volume for design.The design hourly volume thus arrived at need not necessarily be the thirtieth highest hourly volume in all cases.