Red light camera study in Philadelphia

Via Blue Bayou comes this fascinating data point in the red light camera debate.

Evaluating the effectiveness of red-light cameras at two intersections along Philadelphia's busy Roosevelt Boulevard, researchers from the Insurance Institute for Highway Safety separated camera effects from the effects of extending yellow lights to give approaching motorists more warning that signals were about to turn red.

Sometimes these two measures have been introduced simultaneously, which has caused confusion about their relative benefits. The new study reveals that both measures reduce signal violations, but it's the cameras that make by far the biggest difference. They all but eliminated the signal violations that remained after yellow lights were lengthened at the Roosevelt Boulevard intersections.

"Violations virtually disappeared at the six approaches to the two intersections we studied," said Richard Retting, the Institute's senior transportation engineer and lead author of the Institute's new red-light camera study. "This decrease in violations is all the more remarkable because the intersections were such high-crash locations. In fact, they had been identified as having some of the highest crash rates in the nation."

Researchers tallied signal violation rates at intersections before and after extension of yellow lights and again after red-light camera enforcement had been in effect for about a year. The first step reduced signal violations by 36 percent. The cameras reduced the remaining violations by 96 percent. At the same time, violations didn't change much at intersections without cameras in Atlantic County, New Jersey, about 50 miles away.

That's pretty phenominal. Even I wouldn't have expected red light violations to essentially disappear. I wish the study had also included data about accidents, but I daresay you'd need to see a real spike in rear end collisions to outweigh the virtual elimination of T-bones. Whatever you think of red light cameras, is the prospect of wiping out red light running enough to overcome privacy concerns? I can only presume that claims about the cameras being revenue grabs would melt away if they wind up generating little more than token money, but privacy is still an issue. At what point, if any, is the tradeoff worth it for you?

I should note, by the way, that this study stands in contrast to one from California that claimed lengthening yellow light times was sufficient to nearly wipe out red light running. There's a lot of competing data out there, that's for sure. Which is why, as interesting as this is, it would be nice to finally get that data for Houston's experience. I know, I know, it's been less than six months. I'm just saying that we still need to objectively evaluate the cameras here. Who knows how much effect local conditions and driving habits may have on the results? John makes the same observation, and I agree with him completely.

One more thing:

In Philadelphia and elsewhere with camera enforcement, conspicuous signs warn motorists as they approach camera-equipped intersections. The signs posted along Roosevelt Boulevard include images of traffic signals and the words, "PHOTO ENFORCED."

I have been dismissive of the need to highlight camera enforcement with signage, but this suggests they contribute to the overall reduction in violations. If so, then I'll happily retract what I said previously.

UPDATE: I drafted this earlier in the week, and now I see via NewsWatch: City Hall that there's a second study showing a dramatic decrease in crashes at camera-monitored intersections, this time in Virginia Beach.

Posted by Charles Kuffner on February 16, 2007 to Planes, Trains, and Automobiles