Seat belts vs. Air bags

Steven Levitt has a good summary of his research results at the Freakonomics blog [link reached via Marginal Revolution]:

...let me ask you a question: if you could only have one or the other, would you go for the seat belt or the air bag.

It turns out the answer is easy, and my views on this one are much less controversial than on car seats. With Jack Porter, a professor at Wisconsin, I wrote a paper published four years ago that looks at the effectiveness of seat belts and air bags for adults. We found that wearing a seat belt reduced the chance of death by 60-70 percent across all crashes. We estimated that air bags reduce the death rate by 15 percent in frontal crashes, but don't help in partial frontal, side, or rear crashes. (The benefits we found for adults in seat belts were higher than most previous research, and the results on air bags were lower than in most earlier research. But there is nobody who knows the data who would prefer an airbag to a seat belt if it was an either/or choice.)

The bottom line is that to save a life with a seat belt costs $30,000; to save a life with an air bag costs $1.8 mm by our estimates. This makes seat belts an incredibly effective safety innovation. While in comparison, air bags look bad, indeed in the scheme of things $1.8 mm to save a life is pretty good by regulatory standards.

I expect that one thing left out of the statistics is that airbags reduce the number of suicide attempts from running into trees and bridge abutments, especially suicide attempts by people who want their deaths to appear to be accidents, for insurance purposes. You can always drive with your seatbelt undone, but disabling an airbag is more difficult. I have no idea about the size of this effect, but if your car has an airbag, you can't kill yourself this way as easily this way.

Of course you can still do so by pulling out in front of a train or truck (if your car doesn't have side airbags or curtains), but many people contemplating suicide don't really want to inflict that on the driver of another vehicle.