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California: Benefit of Longer Yellow Proves Lasting
Longer yellow at Fremont, California intersection reduces red light running violations by 71 percent over course of 22 months.

Intersection results chart
Public officials and the photo enforcement industry argue the benefits of lengthening yellow lights is temporary. Municipalities that use red light cameras for the most part are highly reluctant to increase the amount of yellow warning time at an intersection, citing the theory that motorists "adapt" to the longer yellow, encouraging even more red light running. New data from Fremont, California suggests the reduction in red light running violations from longer yellows is lasting.

Safer Streets LA Executive Director Jay Beeber charted the performance at the intersection of Mission Boulevard and Mohave Drive where the yellow time was boosted from 4.3 seconds to 5.0 seconds in mid-November. After nearly two years with the enhanced timing, violations remained down by 71 percent.

"I think at this point, with twenty-two full months of 'after' data, we can safely say there is no rebound," Beeber said. "Drivers do not adjust to longer yellow times. And if they are not adjusting at this location, where the time is actually longer, then there can be no argument that they adjust their behavior at locations where the time hasn't been lengthened."

In the months prior to camera enforcement an average of 116 citations were generated at the location each month. That fell to just 33 under the extended timing. The 71 percent reduction figure likely understates the benefit of the longer yellow. The citation totals include alleged left-hand turn violations, and the yellow time for the turn signal remains at the bare minimum legal value of 3.0 seconds.

Fremont boosted the yellow at the location after being challenged by resident Roger Jones, who asked the California Department of Transportation (Caltrans) to investigate. A Caltrans engineer discovered the signal was initially set based solely on the speed limit, but an engineer's observations at the scene confirmed the need for 0.7 seconds of additional yellow warning time.

While a 0.7 second difference in the duration of the yellow warning at an intersection might appear insignificant, the extra margin of safety is critical. The vast majority of straight-through red light "violations" happen when a driver misjudges the end of the yellow light by less than 0.25 seconds -- literally the blink of an eye (view Texas Transportation Institute (TTI) chart). In most cases, a yellow shortened by one second can increase the number of tickets issued by 110 percent, according to a TTI report. Confidential documents uncovered in a San Diego court trial prove that the city and its private vendor, now Affiliated Computer Services (ACS), colluded to install red light cameras only at intersections found to have short yellow times (view documents), thereby maximizing profits.

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