FHWA: Making Our Roads Safer One Countermeasure at a Time

https://safety.fhwa.dot.gov/ provencountermeasures. INTERSECTIONS | PROVEN SAFETY COUNTERMEASURES 12. Yellow Change Intervals SAFETY BENEFITS: 36-50% Reduction in red light running 8-14% Reduction in total crashes 12% Reduction in injury crashes Properly-timed yellow change intervals can reduce red-light running and improve overall intersection safety. Source: FHWA 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. 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 trafic signal timing policies and procedures concerning the yellow change interval. Agencies should institute regular evaluation and adjustment protocols for existing trafic signal timing. Refer to the Manual on Uniform Trafic Control Devices for basic requirements and further recommendations about yellow change interval timing. Source: NCHRP Report 731, Guidelines for Timing Yellow and All-Red Intervals at Signalized Intersections.