The relatively small and declining incidence of traffic-related death accidents in Scandinavia is a result of targeted infra-structural measures and policies. Bicycle accidents represent a large fraction of the total traffic accident load and are often underreported in statistics. We argue that there is scientific evidence of bicycle helmet efficacy with a protective effect on serious brain injury of 63-88%. There is no consensus in favour of the effect of bicycle helmet legislation, although a Cochrane review from 2007 showed a significant reduction of injuries among children.