These studies are made to obtain information on the number, direction and variations in the volume of motor vehicles passing through an intersection or along a major route.
One MP can observe and record information on 1,000 vehicles per hour along a roadway. Two MPs can observe and record information on a normal two-way intersection. More MPs will be necessary if volume exceeds 1,500 vehicles per hour.
Equipment necessary to conduct this study are a wristwatch, field sheets, summary sheets and counting equipment.
Vehicle counts are usually made to cover 10-, 12-, or 24-hour periods, They should be made on weekdays to obtain a normal volume count. The count should begin a half hour prior to peak traffic periods and end a half hour after each peak period. If traffic volume is consistently high during the day and night, an 18-hour count should be made.
The study should be conducted in good weather.
MPs conducting the study should be positioned so they have an unobstructed view of the area. If the count is made at an intersection, MPs should be on diagonally opposite corners.
The field sheet (sample below) is used to record data on an intersection. The number and action of each vehicle entering the intersection is recorded as appropriate. A new sheet is used every one-half hour (every quarter-hour if volume is very heavy).
The summary sheet (sample below) is used to compile data recorded on the field sheets.
The graphic summary sheet (below) is used to indicate the number of vehicles counted and their directional movements during a desired time period.
The route volume graph below is another method of graphically indicating information obtained in this study. The thickness of the bands are related to the traffic volume during a specific period.
The information gathered in a motor vehicle count may be used to:
Study traffic control devices and their effectiveness. The study may justify the existence or need for fixed-time or traffic-actuated signals, the need for stop signs, speed zones, pavement markings, or Military Police on traffic control duty at various locations and times.
Study and evaluate the number of accidents based on volume and directional movement. Generally, special controls are needed if 300 out of 1,000 vehicles make a left turn at an intersection. The need for street lighting and signals can be considered by comparing day and night traffic volume to day and night accident frequency.
Study future needs such as through streets, secondary roads or roadway improvements.
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