Study: Shades of gray for drivers facing yellow lights
Drivers know that green means go, red means stop and yellow often means “Can I make it?” Although the law is clear that yellow means slow down and prepare to stop, many drivers do not. New research sheds light on what factors come into play when a driver decides to run those yellows, and it turns out it’s not just a matter of speed.
Researchers from the University of Cincinnati, funded by the Ohio Department of Transportation, monitored four intersections in suburban areas of Ohio, using video cameras to track more than 1,500 drivers.
They found that cars 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.
Not surprisingly, 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 persists, the more likely it is that drivers will not stop, said Zhixia Li, an engineering doctoral student who worked on the study with his professor, Heng Wei.
In fact, Li said, 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.