Recently came across an excellent paper by Dr. John Adams on the perverse impact of compulsory motorcycle helmet legislation:
The ‘experiment’ conducted in the USA during the latter half of the 1970s in which twenty-eight states repealed laws that made the wearing of motorcycle helmets compulsory is unlikely ever to be improved upon. It comes as close to being an ideal ‘controlled’ experiment as any scientist could wish for; over a few years a geographically diverse sample of states, containing about 47% of the country’s motorcycle population, repealed their motorcycle helmet laws — a measure which it was widely predicted would cause a substantial increase in the numbers of motorcyclists killed. How have the predictions fared?
What happened was that the motorcycle fatality rate increased in states where helmet laws were repealed. This result was widely interpretted by safety ‘experts’ of the efficacy of helmet legislation.
However, what Dr. Adams did was to compare fatality rate against states where helmet laws were not repealed. Result: the fatality rate also increased in helmet-wearing states — by an ever greater factor!
The motorcycle helmet ‘experiment’ provides more strong evidence of the Risk Compensation theory. Safety devices intended to protect drivers instead encourage more risky behavior:
The risk compensation hypothesis is essentially common sense. There is a wealth of evidence from everyday experience that suggests that people’s behaviour is influenced by their perception of risk. People tend to be more cautious when up high ladders than when up low ladders. They tend to take more care when standing on the edge of a high precipice than when standing on a low kerb. They tend to slow down when they encounter bends in the road or patches of fog and to speed up when the road becomes straight or the visibility good — and so on. The possible illustrations of the phenomenon are countless.
There is an impressive amount of propaganda designed to encourage people to believe that they are very much less vulnerable when using seat belts and motorcycle helmets, and common sense suggests that driving behaviour will be influenced by safety devices that diminish the user’s sense of vulnerability. What unaided common sense cannot predict is whether the behavioural changes induced by a safety device will partly, completely, or more than completely nullify the intended effect of the device.