The paradox of bike helmet laws: the fact that wearing a helmet, without question, reduces an individual rider’s risk of injury (recent work estimates an 88 percent reduction in brain injuries and an 85 percent decrease in head injuries) but appears oddly neutral, or worse, for riders at large. Add in the fact that legislation does increase helmet usage among riders, and it would seem to follow that these laws should produce a net public safety benefit. Public education and infrastructure upgrades, as the aforementioned works shows, protect riders considerably even before helmets come into play. Both efforts increase the overall amount of cycling, which provides safety in numbers. Mandatory helmet laws, meanwhile, may discourage riding to the point where public safety as a whole suffers from the relative decrease in physical exercise.
In places where riding is already safe, helmet laws are likely to have a “large unintended negative health impact.” In places where it’s unsafe, the laws may make riding a little safer, but are also likely to distract attention from initiatives, such as infrastructure upgrades, that would be even more effective.