Deadly and Informative Traffic lights


Can someone explain to me why installing a countdown timer on traffic lights increase accidents and injuries?

From Freakonomics

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…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.

Go to that post.

Some commentators made attempts to explain this phenomenon, I only read a few of them, I find them unsatisfactory.

Here are some interesting comments

Is it possible that these numbers will decrease over time as drivers become more aware of what “1 second” really means when they are driving? If you asked the average driver how far they think their car would go in 1 second at 45 miles an hour, I don’t think they would even be close.
I think it would be interesting to “fake the time” (using “longer” seconds that result in a promise of a shorter waiting time) and measure the difference. I belive it makes sense that the (seemingly) shorter waiting time should reduce the proportion of people who decide not to wait. Also it’s interesting question how much longer a second can be so that the cheating is still not noticeable.

The green light timer would likely provide a challenge to drivers who wish to beat it (and therefore go speeding through), whereas the red light timer would assuage jumpy drivers. I cannot tell you the number of times when I was a regular driver that I imagined I saw a green light and almost gunned it.

Just two things I want to add to this discussion. Sense of security allow people to accept more risk, even if its base on false premise. Could it be that a timer on green lights make people feel more secure about driving through the intersection faster with less care? Second, is it because timers are distractive? On green light people need to be driving through the intersection while paying more attention than usual on the timer.

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