A model is developed which permits the quantitative evaluation of the benefit of bicycle helmet laws. The efficacy of the law is evaluated in terms of the percentage drop in bicycling, the percentage increase in the cost of an accident when not wearing a helmet, and a quantity here called the “bicycling beta.”
Empirical estimates using US data suggests the strictly health impact of a US wide helmet law would cost around $5 billion per annum. In the UK and The Netherlands the net health costs are estimated to be $0.4 and $1.9 billion, respectively.
That’s a LOT of money and that lot of money in net health costs could save a LOT of lives. If there’s a net social health cost to mandatory helmet laws then they’re hurting more people than they help. That’s a good reason not to have them if you care about saving lives, or minimising harm, or maximising welfare.
Note that this says nothing about the individual cost of wearing a helmet. In fact, the study assumed a benefit in accidents of wearing one. The point is that people are deterred from riding by the existence of compulsion. It’s still a good idea to wear a helmet if you want to save your brain 🙂