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Study Illuminates Yellow-Light Running

Researchers from the University of Cincinnati, with funding from the Ohio Department of Transportation, used video cameras to monitor over 1,500 drivers at four "high-speed" intersections in suburban Ohio locations. They measured vehicle type, speed, a driver's distance from the intersection when the light turned yellow, and the decision to stop or not in what they referred to as the "dilemma zone."

They found that vehicles traveling in right-hand lanes tended to go through yellow lights, while those on the left did not. Truckers also tended to speed through yellows, as did drivers on streets with higher posted speed limits. Drivers on streets marked by 55 mph speed limits were more likely to run yellows than those in 50-mph zones.

The study found that drivers of SUVs, pickups, sedans, and vans tended to slow down at yellows more than drivers of heavy trucks. Researchers speculated that vehicle weight may be the explanation, as heavy trucks have more difficulty decelerating rapidly than smaller, lighter vehicles.

How long the light remains yellow also matters. (Yellow-light times vary, but typically last about three to five seconds. Traffic engineers base the time on the average speed of the vehicles passing through the intersection.) The longer the yellow, the more likely it is that drivers will not stop, according to the study. With a long yellow, stopping is more dangerous, because other drivers are likely to keep going through the yellow, and someone who opts to stop runs a greater risk of getting hit from behind.