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Why Longer Yellow Times Aren’t Enough to Prevent Crashes and Deaths at Our Intersections

Automated red-light cameras are proven to reduce red-light running and subsequent deadly crashes. Often opponents of cameras will argue that simply lengthening the yellow light time at intersections is enough to prevent red light running. While it is true that longer yellow lights can provide some safety benefit, studies have shown that benefit to be limited, and not enough to significantly reduce the most serious crashes.

Better Together
A 2007 study in Philadelphia found that increasing yellow intervals at intersections decreased red-light running by 36 percent. But when the city added red-light cameras to those intersections, red-light running dropped by 96 percent.

Cities should consider longer yellow signals, along with other engineering countermeasures to help stop red light running. However, it is important to note that longer yellow lights are not a magic fix-all for red-light running. When yellow times get too long, drivers can begin to adapt. Cities should revisit the program over time as drivers become accustomed to the new yellow signal and begin trying to “beat the light” again.

Determining Yellow Light Intervals
State transportation officials provide guidelines for minimum yellow light intervals – the shortest time for a driver to react to the light change and stop or safely pass through the intersection before the light turns red. These intervals are based on reaction time data that cities collect, and can vary state to state.

Redflex supports appropriate signal timing. Our technology can measure and ensure each yellow light is set to the required minimum.

Redflex partners with cities to help them identify photo enforcement solutions that meet their goals, budget and integrate with other traffic safety initiatives. Learn more about our red-light enforcement technology.