DAVID GREENE, HOST:
Many cities and towns have installed a safety feature for pedestrians at traffic signals, you might have seen them. When the signal changes to tell people when to cross an intersection, a timer appears. It alerts pedestrians to how much time they have to cross the road. Well, there's new evidence that the safety feature might actually be having a dangerous and unintended consequence. NPR's Shankar Vedantam joins us each week on this program to talk about social science research. And, Shankar, I know this countdown signal well. I see it as a driver, I see it as a pedestrian. What's the danger here?
SHANKAR VEDANTAM, BYLINE: Well, the danger is that pedestrians are not the only ones who can see this countdown timer. Drivers can see the timer too and as the timer starts winding down to two or three seconds the driver knows the traffic light is about to turn red and that makes some of them speed up to get through the intersection.
GREENE: Well, beyond speeding up, you know, and potentially getting a ticket, is there even more danger here?
VEDANTAM: Yeah, I spoke with Arvind Magesan, he's a researcher at the University of Calgary. And along with his co-author, Sacha Kapoor, they looked at the effect of installing these countdown timers at nearly 1,800 intersections in the city of Toronto. Now, the news is not all bad. The timers lowered the number of accidents involving pedestrians. In other words, when people know how much time they have to get across the intersection, it helps them get across safely or decide not to start in the first place. But the timers also increase collisions between cars. And Magesan told me there was one particular kind of crash that seemed to go up. Here he is.
ARVIND MAGESAN: The largest increase is in rear-end accidents and we think it's because two cars approaching a light, who both see the countdown, the guy behind, he sees the two or three seconds and thinks, oh, the guy in front of me is going to floor it too, I'll floor it and we'll both get through the intersection. Whereas the guy in front thinks, OK, I only have two or three seconds left, I'm going to slowdown. And this is exactly the type of accident that would happen in that case.
GREENE: So this innovation has actually made it less safe to be a driver.
VEDANTAM: Potential. And Magesan and Kapoor also find, David, that the biggest increases in crashes come at intersections that were previously safe intersections. And they think this is because at busy intersections traffic is clogged, you can't really speed through. But at safe intersections, the countdown timers now are causing the drivers to actually speed up. They also find, and this is really disturbing, the effect of installing these timers seems to go up with time. In other words, the more drivers get used to the timers, the more their behavior seems to change. So it may be that I used to say, I'm going to floor it when I see two seconds left, but now I've learned that I can floor it and get through the intersection when there's only one second left. And now I'm going even faster and taking an even bigger risk.
GREENE: Yeah, not a good thing. So this is a real dilemma here. I mean, something that is making pedestrians more safe is actually making drivers less safe. Is there an answer for communities?
VEDANTAM: It's interesting David, but Magesan and Kapoor, suggest the solution might come from policies related to terrorism. Magesan asked me to imagine a scenario.
MAGESAN: If you are in charge of the security of the building and you find out there's a bomb in the building, I don't think your first reaction is to announce to everyone, OK. there's a bomb in the building, because there will be panic and people will get injured or die just trying to escape the bomb.
GREENE: Explain the connection here.
VEDANTAM: So just think about it, David, in terms of what safety officials do, if there's a bomb in the building or there's a threat to public safety, what you want to do is use a code that alerts the guards and the security officials that something is wrong...
GREENE: You hear that, like code nine, code nine.
VEDANTAM: Exactly or you could say paging David Greene and that's a code to all the security officials that something is wrong, without setting off mass panic. Magesan and Kapoor think we should do the same thing with these traffic countdown timers. Install them so that the pedestrians are aware of the timers but the drivers are not. And one way to do that would be to broadcast the timers via audio so that the pedestrians can hear the countdown clock go down, but drivers cannot.
GREENE: Shankar, thanks as always for coming in.
VEDANTAM: Thank you, David.
GREENE: That's Shankar Vedantam, who regularly joins us to talk about social science research. And you can find him on Twitter at @HiddenBrain. You can follow this program at @nprgreene and at @MorningEdition. This is NPR News. Transcript provided by NPR, Copyright NPR.