Raise the Hammer

Mr. Meister, I always wear a helmet and my children always wear helmets, but I have to acknowledge that the matter of bike helmets and safety is anything but straightforward.

As is so often the case in these complex public health issues, common sense is your enemy and it's a big mistake to generalize from anecdotes.

First of all, regardless of whether you wear a helmet, the overall health benefits of cycling, defined as average life-years gained, outweigh the overall risks of cycling by about 20:1. While there are different ways to compare risks, in general cycling is about as safe as driving.

(For an interesting contrast, pedestrians are at significantly higher risk of head injury from automobiles than cylists per distance travelled, but we don't require pedestrians to wear helmets.)

Second, the actual scientific evidence on bike helmets is inconclusive at best. Some methodologies seem to suggest that helmets confer benefits, while others suggest that they do not. It's notoriously difficult to construct a study that controls properly for other contributing factors.

An uncontrolled or poorly controlled study with lots of independent variables tells us nothing about the single variable we are trying to analyze.

Third, in actual crash analyses, the helmets themselves rarely show any evidence of having performed as intended, i.e. the foam has compressed to absorb the energy of the impact. If helmets are not doing what they were designed to do, what exactly are they doing?

Fourth, we need to consider the effect that helmet laws have on cycling rates. The risk of head injury in a cycling crash is high, but the risk of a cycling crash itself is low. Given this, there are two possible approaches to safety:

1. Reduce the risk of injury in a crash; and
2. Reduce the risk of a crash.

Here's where it gets interesting. Mandating bike helmets (which takes approach #1) actually deters people from cycling because it communicates the idea that cycling is dangerous. But when you deter people from cycling, the per-cyclist risk of a crash actually goes up.

Put differently: more cyclists on the road translates into fewer crashes and, hence, fewer head injuries.

It's significant that Copenhagen, a city that knows a thing or two about cycling, does not have a bike helmet law:

"We don't have a law in Copenhagen mandating cyclists to wear helmets," says Brian Hanson, the head of the city's traffic planning department. "We have no problem with anyone wearing a helmet and understand the safety benefits of it. But we've studied the topic many times and the results are always the same: it will decrease ridership significantly. We feel the health benefits of bike riding – active lifestyle, very low carbon emissions, clean air – far outweigh the risks of riding without a helmet." And with ridership still increasing in the city, cycling is becoming even more safe. "The number of accidents has been decreasing year after year. More bikes on the road means it's safer for cyclists," says Hansen.

Fifth, increased helmet use seems to correlate with increased risk compensation, meaning that people who wear bike helmets tend to compensate for the perceived increase in safety with riskier cycling behaviour.

Sixth, and finally, there is growing evidence that drivers also exercise risk compensation when driving near cyclists who are wearing helmets. An astonishing study from the UK found:

Cyclists who wear protective helmets are more likely to be knocked down by passing vehicles, new research from Bath University suggests.

The study found drivers tend to pass closer when overtaking cyclists wearing helmets than those who are bare-headed.

Other studies conducted since then have found similar results.

Comment edited by administrator Ryan on 2011-04-13 13:15:07

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