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Chapter 23

Speed-Delay Studies

These studies are used to determine speed variations along a route at different times; number, location, cause, frequency, and duration of delays, and overall speed and travel time along a route.

Conducting Studies


Two MPs in an unmarked car are required to conduct this study along each desired route. One MP is the driver and the other the recorder.

The MPs need a stopwatch and field sheets.

Routes to be studied should be predetermined. Their lengths and key landmarks should be established.

Peak traffic hours should be determined. The study is made during each of the peak hours on the same day.

For planning, one car should be used for every two miles of route to be checked during peak periods.


The vehicle, called a floater car, enters the mainstream of traffic at the starting point. If more than one car is used, they should start out at 5- to 15-minute intervals.

Start time and odometer readings are recorded on a field sheet (sample below).

Elapsed time and odometer readings are recorded as floater car passes each key landmark.

The location, nature and time of delays are recorded. A stopwatch is used to time delays. Delays are any time the floater car is not moving, such as at stop signs, signals, waiting to make a left turn or because of congestion.

As a rule of thumb, the floater car should pass another vehicle in the traffic stream when it has been passed by a vehicle.

The time and odometer reading is recorded at the completion.


A speed-delay study shows overall speed and moving speeds between specified locations.

It shows delay times, locations and total delay times. It can show cause, frequency and location of delay.

A study made during peak hours and nonpeak hours is good for a comparison study.

A flow map of speeds can be made. The speeds on different routes can be shown by color code or proportional width of bands.

The study locates points of congestion and insufficient road capacity.

An evaluation can be made of traffic control devices and the adequacy of posted speed limits.

The study assists in determining priorities for traffic control and road construction programs.

Studies of emergency vehicles at different times of day, with and without emergency lights and siren indicate if they are actually useful or save substantial time.

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