Mandatory helmet use and the severity of motorcycle accidents: no brainer?

We study the impact of mandatory motorcycle helmet use laws on the severity and volume of road accidents in Uruguay by exploiting a change in the enforcement of the traffic law. Using a differences-in-differences design based on an unexpected change in policy, we report a sharp increase in helmet use and a 5 percentage point reduction in the incidence of serious or fatal motorcyclist accidents from a baseline of 11%. The benefits of helmet use are disproportionately borne by groups more likely to experience serious injuries such as males or young drivers. We find no evidence of other responses in terms of either the volume or type of accidents, suggesting motorcyclists' behaviour did not respond to differences in risk. We show that additional costs of enforcement for the relevant government agencies were negligible and estimate the health benefits of the policy