I haven't listened to the podcast yet, so maybe there is some merit to the car/close shave theory. But lots of bike accidents may not involve a car at all, like not seeing a pothole or sliding out around a curve. As much as I like the contrarian theory, I have to think you're better off with the brain bucket than without.

I suppose it might depend on regional differences too -- where you ride, is traffic the greatest threat?

In the recent Boulder triathalon, a cyclist speeding around a downhill curve crashed into a bear who was loping across the road. (Both were unharmed.) Maybe the bear thought she was experienced?

You're right, Vic. This study only involved car traffic. When I used to ride a lot, it wasn't near traffic, and often not even on paved roads. So I wouldn't give up my helmet in any event. As far as the bear goes, it probably wasn't the triathlete's helmet that suggested her experience on a bike. But once you throw in the camelback and clipless pedals, what's a bear to think?

I haven't heard the podcast yet either, but I've always been fascinated by the fact that diminishing one risk can increase another. Did the podcast discuss whether bicyclists themselves felt "safer" with a helmet, such that they took more risks than without a helmet? I believe that some early risk-analysis studies suggested that after seat belts were made mandatory, people began driving faster because they felt safer due to the belts.

Miranda, if I remember the broadcast right, the professor did all the riding himself. So hopefully he was able to control for his own moral hazard. Incidentally, I should have mentioned in the original post that the podcast is part of Scientific American's "60-Second Science" series. So the podcast is literally only one minute long. Short but sweet.

even if true, the three-inch difference is only one of many factors in bicyclist safety. it is still much better to wear a helmut than not. many accidents do not involve a parallel moving motor vehicle; they may involve a fixed object (I've had that one once without a helmut), a merging vehicle (I've had that one twice), a crossing dog (my bike and helmut both broke), or an openning car door (yes, that one too). also, the risk of serious fatal of debillitating injury is so much higher without a helmut that would swamp the affect from the three-inch difference from parallel vehicles. experienced cyclists are generally more skilled, but they also have much more statistical exposure to all the risks of traffic.

There are too many scenarios that were not included in this experiment. I'd opt for the helmet every time.

Even if the automobiles came closer to the cyclist with a helmet, causing an accident, it would be much better to have a helmet covering your brain. Most broken bones heal much easier than the skull.