Since 1994 in Canada the rate of bicycling injuries, including those to the head, has decreased among young people. In six provinces where helmet legislation was implemented, we observed a steep decline in the rate of hospital admissions for young people with cycling related head injuries (54% reduction) compared with provinces and territories without legislation (33% reduction). In adults over this same period we observed a 26% reduction in the rate of admissions for head injuries in provinces that implemented helmet legislation, compared with no reduction in provinces without legislation. While these results superficially suggest an important effect of legislation, after taking baseline trends into consideration we were unable to show an independent effect of helmet legislation on the rate of head injuries per hospital admission for a cycling related injury one year after the implementation of legislation, either overall or according to the age group of cyclists targeted by the legislation.
Three previous studies have investigated the effects of helmet legislation on bicycle related head injuries using a before and after design and a concurrent comparison group.21
All focused on paediatric populations. In a Canadian study that analysed data from the National Trauma Registry Minimum Data Set (years 1994 to 1997), the same data source used in our study, the authors concluded that helmet legislation was associated with a significant reduction in the rate of cycling related head injuries among Canadians aged 5-19 years.21
Using the same data source but with an extended period of follow-up, over which time two additional provinces implemented legislation, we replicated the results of this previous study in our initial analysis that did not adjust for baseline trends. In our time series analysis, we none the less could not confirm that the reduction in the rate of head injuries was an independent effect of helmet legislation above and beyond the concomitant declining trend in the rate of head injuries observed throughout Canada.
Helmets reduce the risk of injuries to the brain by up to 88%, the head by up to 85%, and the face by up to 65%.10
Laws that mandate the use of helmets increase the chance that cyclists will wear a helmet, especially when they apply to all cyclists.26
Given this evidence, why is it difficult to detect a decrease in hospital admissions for cycling related head injuries after the implementation of helmet legislation? Concurrent interventions that improve cycling safety combined with municipality specific helmet legislation are two possible explanations. The Canadian Cycling Association’s CAN-BIKE programme to promote cycling safety, for example, has been taught in Canada since 1985,31
and local educational programmes, media campaigns, and subsidised or free helmet distribution programmes are also known to have occurred in Canada around the time legislation was implemented (table 1).32
Similarly, changes to cycling infrastructure over the study period (for example, traffic calming, and designated bicycle lanes and routes)38
could have confounded associations with helmet legislation. In provinces and territories without legislation, several municipalities implemented helmet legislation between 1994 and 2003.42
Notably, seven municipalities in Newfoundland and Labrador, including St John’s, the province’s largest municipality, implemented bylaws that may have contributed to the steep decrease in cycling rated head injury rates we observed in this province.44
A third possible explanation for our results is that the effectiveness of helmets is greater for mild and moderate head injuries than for the severe head injuries captured by hospital admission data. Diagnostic and prognostic improvements over time that allowed for the treatment of patients with mild and moderate head injuries in emergency rooms, as opposed to in inpatient hospital wards, could have further impeded our ability to detect an effect of helmet legislation, if one exists.45
While minimal enforcement may compromise the effectiveness of helmet legislation, fear of the police and of fines motivates helmet use,47
and despite nominal fines and few issued tickets, helmet use rose dramatically in provinces immediately after the enactment of legislation (table 1).30
Strengths and limitations of this study
The National Trauma Registry Minimum Data Set captures information on all hospital admissions for cycling related injuries in Canada. Cyclists who die from their injuries before reaching a hospital are not included. Additional data on emergency room visits would have been beneficial, both to make inferences on the association between helmet legislation and milder head injuries and to refine counts of head injuries in small provinces and in the territories. None the less, before 2002 no province or territory systematically reported data on visits to emergency rooms to a national database. The National Trauma Registry Minimum Data Set also makes no distinction between cyclists injured on-road and off-road (for example, while jumping on BMX bikes or mountain biking), yet provincial helmet laws apply only to on-road cyclists. Helmets are standard in off-road cycling, with usage more than 80% in the 1990s and nearly 100% in recent studies.48
This increase, coupled with improvements to helmet design, may have contributed to a reduction in bicycle related head injuries in provinces where off-road cycling is common (British Columbia, Alberta, Quebec).
Data on exposure to cycling are desirable, yet were unavailable for Canada at the time helmet legislation was implemented. Recent data from the Canadian Community Health Survey indicate that bicycle use varies across provinces,26
reflecting differences in climate and cycling infrastructure. Variation in cycling possibly contributes to differences in cycling injury rates between provinces. Within a province, however, the introduction of helmet legislation does not discourage bicycle use and thus permits assessment of helmet legislation on cycling related head injuries.26
One further limitation of our study is the small number of time points, especially preintervention, which may have reduced the power of the segmented regression analysis.25
In small provinces, few observations at each time point resulted in wide confidence intervals.
Strengths of our study include the number of provinces, territories, and years analysed, combined with our use of descriptive statistics and statistical methods for interrupted time series data that explicitly considered baseline trends. This is the first study to use a controlled before and after design to assess the association between helmet legislation and cycling related head injuries in adults, as well as the first controlled study to incorporate background trends in rates of injury. Results from our study are timely and relevant, following ongoing debates in the lay and medical press as to the merit of bicycle helmet laws.53
From 1994 to 2008, we observed a substantial and consistent decrease in the rate of hospital admissions for cycling related head injuries across Canada. Reductions were greatest in provinces with helmet legislation. Rates of admissions for head injuries, however, were decreasing before the implementation of provincial helmet legislation and did not seem to change in response to legislation. While helmets reduce head injuries and their use should be encouraged, this study suggests that, in the Canadian context of provincial and municipal safety campaigns, improvements to the cycling infrastructure, and the passive uptake of helmets, the incremental contribution of provincial helmet legislation to reduce the number of hospital admissions for head injuries is uncertain to some extent, but seems to have been minimal.
What is already known on this topic
- Cyclists are vulnerable road users; head injuries among cyclists account for 75% of cycling related fatalities
- Debate exists about whether or not helmet legislation is an effective strategy to reduce serious head injuries among child and adult cyclists
What this study adds
- When baseline trends in cycling related injury rates were considered, the overall rates of head injuries were not appreciably altered by helmet legislation
- In the context of provincial and municipal safety campaigns, improvements to the cycling infrastructure, and the passive uptake of helmets, the incremental benefit of provincial helmet legislation to reduce admissions to hospital for head injuries is substantially uncertain