Archive for October 1st, 2008

From the Chicago Tribune comes news of a new hotbed of risk on the road: Voting.

“The study found that on average, 24 more people died in car crashes during voting hours on presidential election days than on other October and November Tuesdays. That amounts to an 18 percent increased risk of death. And compared with non-election days, an additional 800 people suffered disabling injuries.”

The authors are none other than Donald Redelmeier and Ronald Tibshirani, whose work appears in several places in Traffic. No word on whether risk was higher for voters for the winning/losing side (as was the case in their “Super Bowl” study); or whether risk was lower in places where voting can be done by mail-in ballot.

“This is one of the most off-the-wall things I’ve ever read, but the science is good,” said Roy Lucke, senior scientist at Northwestern University’s Center for Public Safety. He was not involved in the study, which appears in Wednesday’s Journal of the American Medical Association.

Luckily, I live exactly one block from the public school in which I vote (though I do have to cross a pretty busy street).

Photo by Mikael Colville-Andersen

When I was in the U.K. doing radio interviews for Traffic, I would often get asked if wearing cycle helmets actually made things less safe for cyclists. This happened primarily because the book features rather striking research by Ian Walker, a traffic psychologist at the University of Bath, and this was mentioned in the press kit.

To briefly summarize, in his study (published as “Drivers overtaking bicyclists: Objective data on the effects of riding position, helmet use, vehicle type and apparent gender,” in the journal Accident Analysis and Prevention), Walker outfitted a bike with a device that measured the distance of passing cars. He found, among other things, that drivers tended to pass more closely when he was wearing a helmet than when not (he was struck by vehicles twice, both while wearing a helmet).

This was a surprising, somewhat controversial finding that generated a lot of news coverage. To my mind, Walker’s findings were more interesting for what they said about interpersonal psychology on the road than safety itself; mostly because I felt, and Walker seems to agree, that the primary question of bicycle safety had less to do with the helmet than other factors. As the above photo suggests, cyclists in places like Copenhagen or Amsterdam very rarely wear helmets, and yet they enjoy a much safer ride than in places (like the U.S.) where helmet-wearing seems more ingrained. The argument is often made that those places have protected cycle lanes and the like — though the photo also shows that is not always the case.

But to return to the radio interviews, I often found myself getting frustrated because the radio journalists seemed to want a handy “takeaway” answer: Well, do helmets make cyclists safer or not? The problem was, I really didn’t know (disclaimer: I do wear one, rather out of habit and without much thought other than a fear of New York City streets).

This was a problem I had in trying to give many answers relating to traffic — there are often an endless series of “on the other hand” qualifiers. As with any kind of epidemiological inquiry, traffic presents such a complex system, with so many interacting variables (e.g., do helmets make drivers act less safe) and “confounding factors” and incomplete data sets, that coming up with easy answers is impossible: and anyone who seems to have easy answers probably doesn’t know what they’re talking about. One favorite example of this for me is the nutmeg you hear drivers say, with deeply held conviction: ‘Well I’ve heard it’s not speed itself that’s the problem, it’s differences in speed.’ This is a statement that is true — except when it isn’t. It lacks context, it lacks explanatory power. We would do as well, if not better, to note that every traffic fatality/injury involves speed: If the car wasn’t moving, no one would have died/been injured.

But I was curious as to how Ian Walker, after putting his research into the world and subsequently being asked these sorts of questions, undergoing these sorts of debates, ultimately felt himself about what his findings (at least on several stretches on English roads) had revealed.

Over to you, Dr. Walker:

“The apparently simple query ‘Do bicycle helmets work?’ turns out to be the most complex question I have ever encountered. Since I published my own small contribution to the nightmarish tangle of helmet research a couple of years ago, I have read and answered hundreds of emails on the subject from interested – in both senses of the word – people. I am grateful to Tom for giving me this chance to summarize a few of my disjointed thoughts on the matter.

(more…)