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Monday 21 January 2013

Traffic volume count can be collected by the following methods:-
  1. Manual counting:- In this method, a field team of enumerators (traffic persons) is deputed to record traffic volume on the prescribed record sheets in a specified period. A sample of the field sheet which is used for traffic counts.
    The main advantage of this method  is that the field team can record the type and direction of vehicles. However, it is not practicable to do manual counting for all the 24 hours of the day and on all days round the year. But this period is commonly used due to its specific advantage over the method of automatic recorders.
  2. Automatic recorders :- In this method, the total number of vehicles crossing at a road intersection in the desired period is automatically recorded by a mechanical recorder. These recorders are either fixed type or portable type and may record the data by different methods discussed below.
  • Photo electric cell method :- In this method, the automatic recorder is actuated by the interruption of a light beam falling on a photo electric cell placed on the road side as a vehicle passes.
  • Electrical method :- In this method, the automatic recorder is actuated by closing of an electric circuit by the passage of a vehicle.
  • Pneumatic method :- In this method, the automatic recorder is actuated by an air switch attached to a flexible hose pipe stretched across the road over which the vehicle passes.
          The main advantage of the methods of automatic recorders is that they can work throughout the day                      and night for the desired period, recording total hourly volume of traffic. But the disadvantage of this method is that the automatic recorders cannot record the type and direction of vehicles. Moreover, the data is not as accurate as  in case of manual counting since two or more vehicles going abreast will be recorded as a single unit.

     3.  Moving car method :- In this method, the number of vehicles met, overtaken and the time taken to     travel are noted by the observer moving in a car once against the traffic and second time alongwith the traffic. Then the volume of traffic is calculated by the following relationship:-
                                   V= x+y
                                         -----
                                         ta +tw

Where, V= Vehicles per minute in one direction.
            X= Number of vehicles met when moving against the desired direction in  ta  minutes.
            Y= Number of vehicles overtaken while moving alongwith the traffic in the direction in  tw minutes.
The accuracy of this method depends upon the number of tests conducted.

1 comments:

  1. Which of the following is not the method of collecting traffic volume count

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