Priceonomics

You are driving toward an intersection and the light is green. But on either side of the road, a sign with a blinking orange hand is counting down: 6, 5, 4… 

The sign is meant for pedestrians. It informs little, old ladies and parents with adorable 5 year olds when to cross the street. But you as a driver know that as soon as the clock runs out, the stop light will turn yellow and then red, leaving you stuck at the intersection for several minutes. It doesn’t look like you’ll make it. What do you do?

If you’re anything like the residents of Toronto, where a large number of “countdown signals” were installed in 2006-2008, you’ll likely accelerate, tailgate the car in front of you as close as you dare, and quite possible bump the car in front of you.

This is the conclusion of a recent paper on “The Costs of Public Information” (pdf). By looking at traffic data from before and after the installation of countdown signals in Toronto, researchers found that the signals increase the number of collisions at intersections by 5%. 

In one respect, the countdown signals did operate as intended. By knowing whether they had enough time to cross the street before the light changed, pedestrians suffered fewer injuries. But that improvement was more than offset by the number of rear end accidents between cars. 

It’s hard to say which type of accident is preferable. Pedestrians are more vulnerable, but incidents involving pedestrians typically happen at very low speeds and result in minor injuries while car collisions occur at higher speeds. 

But the paper’s findings do suggest that, following the law of unintended consequences, a decision meant to improve public safety actually had the opposite effect. The authors of the study suggest selectively installing countdown signals at intersections with a history of being dangerous for pedestrians.

As the authors point out, there is an analogy between the traffic lights and emergencies in public places. If there is a fire in a crowded theater, the staff will not announce it over the loudspeaker. Instead, (at least in Britain), they “page Inspector Sands” to the location of the fire. Inspector Sands does not exist, it is a code understood by the staff. They can then put out the fire and, if necessary, begin evacuating patrons. If they merely announced a fire over the intercom, they could risk a dangerous stampede to the exit.

Similar codes exist in public venues around the world. Many hospitals have a different color or number corresponding to different emergencies - a fire, bomb threat, or shooting - to alert staff to the situation without causing a panic. 

This suggests a solution to the problem with countdown signals. Just as crucial information is only announced to the staff who need it, the signal needs to reach only the pedestrians. By switching the countdown to a spoken one that drivers can’t hear, pedestrians could benefit without drivers aggressively tailgating each other to beat the light.

More information is usually better. But there are situations that benefit from a little discretion.

This post was written by Alex Mayyasi. Follow him on Twitter here or Google PlusTo get occasional notifications when we write blog posts, sign up for our email list



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