Friday, March 14, 2008

Do traffic light countdown timers reduce accidents?

Freakonomics has a report on Taiwan's innovation: traffic light countdown timers.
About a year ago in Taiwan, they started installing countdown timers at traffic lights at a number of intersections. Some counted down the amount of time remaining till a green light turned yellow and then red, while others counted down the amount of time remaining before a red light turned green. Some intersections had both.

It's a fact that a certain number of accidents are caused both by people who jump the gun on the red light, and those who try to make it through the intersection after the light has already turned red. Ostensibly, the reason for the timers was to give people more precise information about exactly how much time they had remaining before the light changed, in the hope of reducing accidents.

The results are quite interesting. A research institute within Taiwan's Ministry of Transportation released a report showing that at 187 intersections which had the timers installed, those that counted down the remaining time on green lights saw a doubling in the number of reported accidents, with a 33 percent increase in the number of injuries, while those that counted down until a red light turned green saw a halving in both the number of reported accidents and injuries. Intersection that had both red and green light timers saw a 19 percent increase in reported accidents and a 23 percent increase in injuries.

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