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Spot Speed Instantaneous speed of a vehicle at a specified location. Time Mean Speed Average of instantaneous speeds of observed vehicles at a spot over a period of time. v t = Σq i v i /Σq i Space Mean speed Average of the speed measurements at an instant of time over a space. v s = Σq i /Σ(q i /v i ) 2

Design of geometric features. For regulation and control of traffic operations. To establish safe speed limits. Location and size of traffic signs. For analyzing causes of accidents. To study the traffic capacity, problems of congestion on roads etc. To decide speed trends. 3

Methods available for measuring spot speed : Radar Speedometer which automatically records instantaneous speed. Photographic method. Pressure Contact Tubes Enoscope Direct Timing Procedure 4

Instrument directly measures speed. Speed of vehicles in both directions can be observed. 5

Time-lapse camera photography can be used. Photographs are taken at fixed intervals of time(say one second per frame) on a special camera. By projecting the film on a screen, the passage of any vehicle can be traced with reference to time. Images by video cameras can be also used. 6

Pneumatic tubes are used. At both reference points, a flexible rubber tube is fastened to the pavement in perpendicular direction to the path of vehicle travel. A vehicle crossing the tube compresses the air in it,actuating an air impulse switch. When the air impulse is sent, it activates an electromagnetically controlled stopwatch in the hands of observer. When vehicle passes over second tube, stopwatch automatically stops. Reading is noted by observer. 7

Enoscope Also known as mirror box L-shaped box, open at both ends,with a mirror set at 45 ˚ to the arms of the instrument. 8

Direct timing Procedure Simplest method Two reference points are marked on the pavement at a suitable distance apart and an observer starts and stops stopwatch as a vehicle crosses these two marks. 9

From known distance and time, speed can be calculated. 10 Average Speed of traffic (kmph) Recommended Trap Length (m) Below Over 6575 Trap Length:

Average speed of vehicles From spot speed data, distribution tables are prepared by arranging the data in groups covering various speed ranges and number of vehicles in each range. Arithmetic mean is the average speed. Cumulative speed of vehicles Graph is plotted with average values of each group on X-axis and cumulative % of vehicles travelling at different speeds. 11

85 th percentile speed: Speed at or below 85 % of vehicles are passing the point of highway. Only 15 % of vehicles exceed the speed at that spot. Drivers exceeding 85 th percentile speed are considered to drive faster than the safe speed. Hence 85 th percentile speed is adopted for Safe speed limit at that zone. 50 th percentile speed: median speed. 98 th percentile speed: used for geometric design. 15 th percentile speed: represents the lower speed limit. 12 ith Percentile Speed: The spot speed below which i percent of the vehicles travel, e.g. 85 th -percentile speed

Observations Table: 13

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Frequency distribution curve

Cumulative frequency distribution curve

Study Locations

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