What's wrong with new cycle helmet law

News of a helmet law being passed in Jersey has re-opened the debate about the need for such laws. We attempt to understand some of the complex arguments.

Talking about cycle helmet wearing and the effectiveness of laws to make it compulsory is always difficult. Any discussion tends to focus attention on a very small proportion of the most serious injuries resulting in a public misperception that the relative risks of cycling are high compared to similar activities.

Last month the parliament in Jersey passed a law requiring all children under 14 to wear cycle helmets. The Scrutiny Office in Jersey commissioned a consultancy report from The Transport Research Laboratory (TRL) to "review the literature relating to the proposed legislation and its likely effects on cyclist injuries, and cycling activity"

Complex science

There is a complex array of factors in understanding the dynamics of any cycle crash and the medical outcomes. Another set of factors affect the severity of impacts and the likelihood of a crash happening. Further, when considering public policy, comparisons between potential health benefits to millions need to be weighed against changes in injury severity for relatively few people.

In a recent article for the British Medical Journal, Ben Goldacre and David Spiegelhalter concluded "In any case, the current uncertainty about any benefit from helmet wearing or promotion is unlikely to be substantially reduced by further research".

Given the complexity of the analysis of cycle helmet benefits the TRL press release expressed a surprisingly high level of certainty "that legislation requiring the wearing of cycle helmets in Jersey will prevent head and brain injuries". It is unfortunately very common for research press releases to overstate results in a way that leads to mis-information and confusion. Most of the press comment is based on this press release not the content of the TRL report.

Pros and cons of helmet legislation

The actual TRL report concluded that the legislation "can be expected to have a beneficial effect on the injury rates of those impacted by the legislation, especially in collisions that do not involve motor vehicles". That is actually a weak conclusion because there was no attempt to measure how big the total effect of the legislation might be.

Many people claim that introducing compulsory helmet legislation tends to put people off cycling by encouraging a climate of fear due to over-emphasizing the risks of serious injury.

There are considerable health benefits from more people cycling as shown in the Mayor's of London Infrastructure Plan 2050 consultation documents.

This table illustrates the potential impacts on Londoner's health assuming different patterns of travel, measured in potential years of good health (DALYs). More cycling is associated with better health.

In Australia, where cycle helmets have been compulsory in most areas since 1990's, Piet de Jong, professor of Actuarial Studies at Macquarie University has developed a model to evaluate helmet laws. He compared the dis-benefits of less cycling due to a compulsory helmet law with the potential injury reduction benefits of a reduction in injury severity. He concluded that only under extreme, theoretical circumstances do mandatory helmet laws not end up costing the healthcare system more from long term ill health due to less physical activity.

Crucial questions

The crucial question is: do compulsory helmet wearing laws reduce cycling or not? The TRL report asserts that if these reductions occur "they are likely to be small and short term". This is important because if cycle use falls after a law it is difficult to tell if a drop in the number of injuries after legislation is only due to a fall in cycling or to a protective effect of helmets. It also leads to a conclusion that  there are no long term negative health effects.

The TRL report accepts at face value recent Australian research casting doubt on the observations of a fall in cycling after compulsory helmet wearing laws were introduced. Therefore TRL conclude that there are no health impacts.

They also base their conclusions about the benefits of helmet legislation on other research some of which does not consider differences in cycle usage and so cannot distinguish between protective effects and usage effects. TRL refrain from evaluating how effective helmet legislation is in reducing injuries or injury rates in the real world (footnote p.30). Instead they concentrate on bio-mechanical predictions of helmet effectiveness that are not linked real injury data.

Do compulsory helmet laws lead to less cycling?

How good is the Australian research from Olivier et al. (2013) suggesting no fall in cycle use resulting from helmet laws?

A number of recent research papers from the University of New South Wales have suggested that there was no long term fall in cycle use when helmet laws were introduced in 1991.

The examination of changes in cycle use in New South Wales depends on two assumptions. Firstly that counts taken in September 1990 (Australian spring time) are comparable with those taken in April 1991 (Australian autumn) because it is thought that weather is likely to be the same. Reading the original research reports shows a significant difference in actual weather during data collection times. The subsequent yearly surveys show a consistent decline in cycling.

Secondly data missing from the first survey is estimated by comparing one set of observations where the instructions were to not record anyone over 20 years old with observations in later years where the instructions were to record all adults of any age. The estimated data is bound to be incorrect and to lead to false conclusions.

Data table showing (in red) data estimated by comparing some counts excluding most adults with counts including all adults.

There may be other problems with the recent reassessment of the 1990s data which have yet to come to light. It is, however, difficult to assume that the observed 47% fall in children being allowed to cycle in New South Wales did not have long term impacts on the amount of cycling of those children and their families in later years.

Arguments continue

As we noted at the beginning, it is unlikely that science can deliver a definitive answer to the evaluation of the benefits, if any, of helmet legislation. The arguments and confusion will continue.

The TRL report only became available a few hours before the States of Jersey voted for a law forcing children under 14 to wear helmets while cycling. It is unfortunate that the deputies did not have more time to subject the report to proper scrutiny.

CTC, the national cycling charity, came to the conclusion that Jersey's under-14 helmet law "will harm public health and the island's reputation for family cycling".


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