Evidence exists to suggest that bicycle helmets may reduce the risk of head injuries to cyclists, however helmets are not uniformly worn by all bicycle users. Legislation has been enacted in some countries and jurisdictions to mandate helmet use by cyclists, however the issue remains controversial with opponents arguing that helmet laws may inhibit people from bicycle riding and thus from gaining the associated health benefits, or that other countermeasures (e.g. improved road safety) may have been responsible for the observed decline in head injuries.
To assess the effects of bicycle helmet legislation on bicycle-related head injuries and helmet use, and the occurrence of unintended adverse consequences.
We searched Cochrane Central Register of Controlled Trials (The Cochrane Library 2009, Issue 1); The Cochrane Injuries Group specialised register (searched July 2009), MEDLINE (Ovid SP) (1950 to April 2010), EMBASE (Ovid SP) (1980 to April 2010), CINAHL (EBSCO) (1982 to April 2010), TRANSPORT (Ovid SP) (1988 to September 2009) and other specialist electronic databases. In addition we searched government websites, handsearched selected journals and examined the reference lists of selected publications.
We included studies that reported changes in either the number of head injuries, helmet use or bicycle use post- versus pre-legislation. Only studies that included a concurrent control group and which reported on the effect of legislation implemented at either the country, state or province wide level were included.
Data collection and analysis
Two authors independently extracted data and assessed methodological quality. The data were not appropriate for meta-analysis, thus the results of the included studies have been reviewed narratively.
Six studies, all with a non-randomised, controlled before and after study design met the inclusion criteria. For each of the studies, bicycle helmet legislation had been enacted for children only. Adults were used as controls in five of the studies, whilst jurisdictions with no helmet legislation were used as controls in the sixth. One study reported on bicycle related mortality while three of the studies reported on changes in head injury rates and three reported on changes in helmet use. There were no included studies reporting change in bicycle use or other adverse consequences of legislation. In three studies, statistically significant decreases in mortality or head injuries were reported following the implementation of helmet legislation compared with controls, whilst one reported a non-statistically significant decline in head injuries. Bicycle helmet use increased statistically significantly post-legislation in all three of the studies reporting on helmet use.
Bicycle helmet legislation appears to be effective in increasing helmet use and decreasing head injury rates in the populations for which it is implemented. However, there are very few high quality evaluative studies that measure these outcomes, and none that reported data on possible declines in bicycle use.
Plain language summary
Bicycle helmet legislation for the uptake of helmet use and prevention of head injuries
Cycling is a popular past-time among children and adults and is highly beneficial as a means of transport and obtaining exercise. However, cycling related injuries are common and can be severe, particularly injuries to the head.
Bicycle helmets have been advocated as a means of reducing the severity of head injuries, however voluntary use of helmets is low among the general population. Bicycle helmet laws mandating their use have thus been implemented in a number of jurisdictions word-wide in order to increase helmet use. These laws have proved to be controversial with opponents arguing that the laws may dissuade people from cycling or may result in greater injury rates among cyclists due to risk compensation. This review searched for the best evidence to investigate what effect bicycle helmet laws have had. There were no randomised controlled trials found, however five studies with a contemporary control were located that looked at bicycle related head injury or bicycle helmet use. The results of these studies indicated a positive effect of bicycle helmet laws for increasing helmet use and reducing head injuries in the target population compared to controls (either jurisdictions without helmet laws or non-target populations). None of the included studies measured actual bicycle use so it was not possible to evaluate the claim that fewer individuals were cycling due to the implementation of the helmet laws. Although the results of the review support bicycle helmet legislation for reducing head injuries, the evidence is currently insufficient to either support or negate the claims of bicycle helmet opponents that helmet laws may discourage cycling.