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Bicycle helmets and the law

BMJ 2013; 346 doi: (Published 12 June 2013) Cite this as: BMJ 2013;346:f3817

Re: Bicycle helmets and the law

One recent study of the effect of legislation for Australia considered a range of issues, including cycling levels, fatalities, injuries, health and enforcement (ref 1). A negative cost benefit ratio was reported:

‘Cost benefit ratio is (0.408 x 20)/(0.25 x 0.3) = 8.16/0.075 =109
The cost factor against helmet laws is then more than 100 to 1. Put simply, helmet laws are not worthwhile because the health loss is far greater than the possible gains.’

In addition, the injury risk compared to cycling levels was found to have increased.

It concludes with, ‘Based on available evidence, helmet laws should be repealed because several reports raise serious doubts whether helmet wearing improves safety overall and the resulting harm to health, environment and social consequences are considerable’.

The New Zealand helmet law evaluation reported:

"This evaluation of NZ’s bicycle helmet law finds it has failed in aspects of promoting cycling, safety, health, accident compensation, environmental issues and civil liberties. It is estimated to cost about 53 lives per year in premature deaths and result in thousands of fines plus legal aspects of discrimination in accident compensation cases. Road safety and cyclist’s safety should be improved by coherent policies, which support health, the environment, and without the legal requirement to wear a helmet (ref 2).

For Canada concerns have been expressed about discouraging cycling and a possible higher accident rate resulting from helmet use (ref 3, 4).

A recent report on the USA also indicates a discouraging effect from helmet legislation and the safety outcome is questionable (ref 5).

One question that emerges is why helmet use should increase the accident rate. One reason to investigate is when cyclists hit potholes. A rider travelling at about 12mph (20km/hr) or 5m/s and hitting a pothole, for example 300mm wide, may take about 0.05 seconds to cover the distance. A typical reaction time may be about 0.1- 0.2 seconds, so the rider would not have time to react to any forces from the pothole impact. Reportedly up to 10g forces to helmets can occur from hitting deep potholes (ref 6). Helmets may add 5% to 10% extra to the bare head mass. The forces on the head would likely be higher for a helmet wearer and in random directions and the out of balance forces from the impact on the rider and bicycle may vary in direction. As a consequence wearing a helmet increases the risk of falling by incurring extra forces that the rider may not have time to react to. Perhaps some research could investigate this issue.

1 Clarke CF, Evaluation of Australia's bicycle helmet laws, The Sports Science Summit, London UK 2015

2 Clarke, CF, Evaluation of New Zealand's bicycle law, NZMJ 10 February 2012, Vol 125 No 1349 accessed 11.1.2014

3 Clarke CF, Response to; Helmet legislation and admissions to hospital for cycling related head injuries in Canadian provinces and territories: interrupted time series analysis,

4 Clarke CF, Evaluating bicycle helmet use and legislation in Canada,

5 Gillham C, Rissel C, Children’s cycling participation, injuries, fatalities and helmet legislation in the United States, World Transport Policy and Practice Volume 21.1 January 2015,

Competing interests: No competing interests

27 January 2015
Colin F Clarke
Stamford Bridge, York YO41 1BU