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FHWA Home / Safety / Proven Safety Countermeasures / Proven Safety Countermeasures - Yellow Change Intervals

Proven Safety Countermeasures

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For more information about this Proven Safety Countermeasure, visit the Office of Safety's Signalized Intersections: An Information Guide's Vehicle Timing –Vehicle Clearance..

Yellow Change Intervals

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U.S. Department of Transportation
Federal Highway Administration

FHWA-SA-17-057

Icon showing a yellow light on a stoplight.

Yellow Change Intervals

Safety Benefits of Well-Timed Yellow Change Intervals:

36-50%
Reduction in red light running

8-14%
Reduction in total crashes

12%
Reduction in injury crashes

Source: NCHRP Report 731, Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections.

At a signalized intersection, the yellow change interval is the length of time that the yellow signal indication is displayed following a green signal indication. The yellow signal confirms to motorists that the green has ended and that a red will soon follow.

Properly-timed yellow change intervals can reduce red-light running and improve overall intersection safety.
Source: FHWA

Since red-light running is a leading cause of severe crashes at signalized intersections, it is imperative that the yellow change interval be appropriately timed. Too brief an interval may result in drivers being unable to stop safely and cause unintentional red-light running, while too long an interval may result in drivers treating the yellow as an extension of the green phase and invite intentional red light running. Factors such as the speed of approaching vehicles, driver perception-reaction time, vehicle deceleration rates, intersection width, and roadway approach grades should all inform the timing calculation.

Transportation agencies can improve signalized intersection safety and reduce red-light running by reviewing and updating their traffic signal timing policies and procedures concerning the yellow change interval. Agencies should institute regular evaluation and adjustment protocols for existing traffic signal timing. Refer to the Manual on Uniform Traffic Control Devices for basic requirements and further recommendations about yellow change interval timing.


For more information on this and other FHWA Proven Safety Countermeasures, please visit
https://safety.fhwa.dot.gov/provencountermeasures.

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Page last modified on October 18, 2017
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