Why Countdown Clocks for Pedestrians Cause Crashes

By Sarah Zhang on at

As a frequent traveller by foot, I love countdowns at crosswalks. They tell me whether I should wait two seconds or leisurely walk across in 15. And indeed, these countdowns do make pedestrians safer. But it turns out that countdowns actually cause more crashes between cars. Here's why.

The answer is, weirdly enough, too much information. We all know how drivers who like to speed up at a yellow light. Countdown clocks are meant for pedestrians, but they also inadvertently tell drivers about upcoming red lights — with even more detail and more lead time than yellows. While we should, in theory, act rationally with that extra information, drivers actually just tailgate more aggressively to race through before the light changes.

NPR has a fascinating story about this phenomenon based on a study done in Calgary. When the city decided to install pedestrian countdown clocks at its intersections, there were five per cent more crashes between cars at intersections, or roughly 21.5 more collisions every month. The number of car-pedestrian crashes, however, actually went down.

That presents a dilemma: how do we make intersection safer for pedestrians without making them more dangerous for cars? The study's authors propose an idea based on how officials might deal with terrorism. If you announce a bomb in a building, you're likely to get a mass stampede toward the exits. But a code phrase could alert the guards to get people out with less panic. Perfect transparency may not always be a good thing. At intersections, this might mean an audio countdown that pedestrians can hear but drivers cannot. In this case, less information might be safer. [NPR]

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