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How much are helmet laws justified?

This commentary assesses the evidence for each of the criteria that should be satisfied before a helmet law is introduced. These criteria are summarised here.

There must be clear evidence that cycling is especially dangerous, compared with other common activities

People who cycle regularly live longer and experience healthier lives than people who do not cycle [1]. Cycling cannot therefore be more dangerous than other common activities. Data from France shows that cyclists are less likely to be killed than other road users [2]. In the UK and other countries, cycling is safer than walking [3]. When the health benefits of cycling are taken into account, cycling is safer than any other mode.

There must be evidence that cycling is unusually productive of head injuries

The risk of head injury to children when cycling is only slightly greater than the average for all activities. The risk when walking is significantly higher than the average [4]. In France, cyclists are less likely to suffer head injury than other road users [2]. As cyclists live longer, on average, than non-cyclists, their risk of head injury cannot be exceptional.

The injuries that might be mitigated by a helmet must be of genuine concern

The great majority of head injuries are minor and have no lasting effect. As such, they are of no more concern than minor injuries of any kind.

There must be a high level of scientific evidence that bicycle helmets are effective in reducing the rate of injury to cyclists

Although small-scale case-control studies claim to demonstrate that helmets are effective in reducing head injuries, large population studies, based on more diverse data sources, show no such benefit. Furthermore most pro-helmet studies have been criticised for fundamental methodological errors. There is thus no net scientific consensus that cycle helmets are effective. See: Contradictory evidence about the effectiveness of cycle helmets.

The benefits to society and others of mandatory helmets must be convincingly demonstrated

In societal terms, helmet laws means less cycling which leads to poorer public health. The costs to society of illnesses such as heart disease, which result in part from a more sedentary lifestyle, greatly outweigh the costs of the relatively few head injuries that cyclists sustain. The loss of choice in transport modes for people that do not wish to wear helmets is another disbenefit.

There must be widespread agreement that the potential benefits of compulsory cycle helmets outweigh the infringement of personal liberty and other disbenefits

When surveys have been undertaken, there has often been found to be a majority of the public in favour of helmet laws. However, this is against a background of information about helmets that is almost entirely one-sided and often exaggerated and emotional in its support for helmet wearing. Also, people are more often in favour of helmets for other people than for themselves. Public opinion must be better informed to be a valid instrument for decision making on such a controversial issue.

There must be good evidence to suggest that compulsory helmet wearing will not make the public health and safety benefits of increased levels of cycling harder to obtain

The overwhelming evidence is that enforced helmet laws lead to very much less cycling, particularly for utility journeys and amongst young people. See: Survey of existing laws. This leads to a loss of health benefits for those who no longer cycle and to society as a whole.

Moreover, just as cycling becomes safer the more people who do it [5], so less cycling leads to reduced safety for those who continue to cycle. Helmet laws are equally bad for those who choose to wear a helmet without a law, since they can achieve no additional benefit but along with everyone else will be at greater risk in traffic due to erosion of the safety in numbers effect.

Where the same solution has been tried elsewhere, there must be unambiguous proof that it has worked

The survey of existing laws shows no case where there is good evidence that the rate of head injury has fallen relative to cycle use. In all cases where laws have been enforced, cycle use has declined, usually by more than the increase in helmet wearing.

There must be no evidence of harmful side-effects from helmet use, such as a greater likelihood of being involved in a crash or an increase in the severity of some types of injury

Many claims are made by helmet wearers that their helmet has 'saved their life'. The number of such instances seems well in excess of the number of head injuries suffered by bare-headed cyclists. More research is needed to clarify whether helmeted cyclists are more likely to crash, but there is already some evidence that helmeted riders are more likely to hit their heads if they do fall.

References

[1] Andersen LB, Schnohr P, Schroll M, Hein HO. All-cause mortality associated with physical activity during leisure time, work, sports, and cycling to work. Arch Intern Med 2000;160(11):1621-8.
[2] See: Head injuries and cycling safety in France.
[3] Wardlaw M. Assessing the actual risks faced by cyclists. Traffic Engineering and Control 2002;43:420-24
[4] Franklin JA, Chapman G. Quantifying the risk of head injury to child cyclists in England: an analysis of hospital admissions data. BHRF, 2005.
[5] Jacobsen PL. Safety in numbers: more walkers and bicyclists, safer walking and bicycling. Injury Prevention, 2003;9:205-209.