Background Cycling is a physical activity with many health and environmental benefits. There are inherent risks while cycling and bicycle helmets have been proposed as a means to mitigate head injury along with crash avoidance strategies such as separated cycling infrastructure. Twenty-seven countries around the world have enacted bicycle helmet legislation (BHL) to increase helmet usage among cyclists. Critics of BHL often claim legislation deters cycling uptake.

Methods Five electronic databases (MEDLINE, EMBASE, COMPENDEX, SCOPUS, WEB OF SCIENCE) were searched to identify relevant studies. Two authors independently assessed records retrieved in adherence to the PRISMA statement. The included studies reported data on cycling exposure pre- and post-legislation.

Results 22 studies with data from 6 countries covering 16 jurisdictions were identified from the peer-reviewed and grey literature. The methods used to measure cycling include direct observation at fixed locations, self-reported surveys, hospital data, police-reported crashes and movement counters. Most studies had a single pre-legislation observation making it impossible to estimate existing trends. Although BHL exists in 27 countries, our systematic review identified studies from Australia, Canada, New Zealand, Spain, Sweden and the United States.

Conclusions In our preliminary results, most studies found no or conflicting evidence of reductions in cycling following BHL. In the few studies reporting reductions in cycling following BHL, these could be due to existing trends or a general shift from active transport modes to personal motor vehicle travel. Due to the lack of data across most jurisdictions with BHL, caution should be exercised when interpreting these results.