The effects of New Zealand’s cycle helmet law: The evidence and what it means.

Our post on the effects of the NZ cycle helmet law  has had more views than any other so far on . Prompted by this, below we:

(i)              Give fuller references to the evidence.

(ii)             Suggest the reason for the observed changes (particularly the apparent adverse effects on cyclist casualty rates).

(iii)              Look at helmet advocacy in the context of a car dominated “road safety” culture.

 The evidence

1.     Specifically on New Zealand (and also for the similar case of Australia which also has a mandatory cycle helmet law), peer-reviewed scientific analysis is provided by Dorothy Robinson in Head Injuries and Helmet Laws in Australia and New Zealand 

 2.     The main collection of evidence for New Zealand is in “Mandatory bicycle helmet law in New Zealand , to be found on Chris Gilham’s web site Mandatory bicycle helmet law in Western Australia .

 3.      On cycle helmets generally, the main site to visit  is , which  is administered by the Bicycle Helmet Research Foundation (BHRF), an incorporated body with an international membership, the object of which is: “to undertake, encourage, and spread the scientific study of the use of bicycle helmets, in the context of risk compensation and sustainable transport”. BHRF also considers the effect of the promotion and use of helmets (whether on a voluntary or mandatory basis) on the perception of cycling in terms of risk; and the contribution and potential of cycling towards maintaining physical and mental health.

 4.     Also take a look at the CTC’s “Cycle helmets: An overview of the evidence” 


What happened in New Zealand and why?

The graph shown  indicates that the mandatory cycle helmet law is associated both with a decline in cycling, and an increase in cyclist casualty rates. The evidence points to this occurring because:

  1.   The helmet law put people off cycling, both because of the inconvenience of wearing  helmet, but also by dangerising cycling – seeing it as something which is inherently hazardous.
  • So much for the decline in cycling. Although other factors associated in a car-dominated transport system may be at fault as well, the law was associated in reducing the numbers of people engaged in a healthy activity, and one which is also quite low risk. But also:

 2.      Safety in Numbers: The decline in cycling is itself associated with an increase in cyclist casualty rates. A reason for this is often known as “Safety in Numbers” (SiN), but is actually a phenomenon known about in studies of road casualties for some time. Essentially it is a version of behavioural adaptation or risk compensation. In this case, the implication is that other road users become more used to the presence of cyclists the more of them there are, and take more care.

SiN does not mean that all that has to be done for the safety cyclists is to increase their numbers, nor does it imply that it will always work – there is normally a critical level at which other road users reach the increased awareness level. But it does mean that casualty rates for cyclists will increase with a decline in cycling.

3.      Risk compensation: Risk compensation (RC) is the big open secret of academic research on safety on the road. Everybody knows it occurs (at the very least, the idea that people do not adapt to perceived danger is highly improbable). In this case we are dealing with the adaptive behaviour of helmet wearers – RC by people when they wear a helmet compared to when they don’t. To a lesser extent RC also means the possible changes in behaviour by other road users towards those who are now considered to be less vulnerable.

As an illustration of risk compensation by the wearer, consider the following from an interview with one of the heroes of British cycle sport: Malcolm Elliott, first British winner of a Grand Tour Competition jersey (green jersey, Tour of Spain)


Malcolm Elliott wins a stage of the Milk Race in 1983, before shell helmets were worn, (note the “leather hairnet”)

Interviewer: “Cotton cap or helmet?

Malcolm Elliott: “For 95% of the time, Helmet. The other 5% I’ll go without, if its very hot, which usually means I’m in Spain or Mallorca. I feel a little safer there due to better attitudes towards cyclists. I’m always aware I’m more vulnerable when not wearing, the same feeling you get in a car without a seatbelt, and take extra care.” (my emphasis). On the effects of seat belt wearing see this post.


4.       Helmet effectiveness: In addition, there are doubts about the potential effectiveness of cycle helmets against likely impacts on the head, as well as the relative importance of other impacts on the body (for which helmets are not supposed to have effectiveness). The design is for low-speed impacts. There is significant debate about the amount of energy which they can absorb and the significance of breakage on impact.

All of the above refer specifically to the effects of a law, but 2 – 4 apply to cycle helmet wearing without legal compulsion.

In analysing helmet wearing the importance of a law, such as those in new Zealand or Australia, is that the effects of helmet wearing across most of the population (of cyclists) can be observed. There are, as always, issues about interpretation of the evidence. In particular, casualty rates have to be looked at in the context of general changes in the safety of road users of all types: possible benefits from helmet laws may be claimed by helmet advocates when in fact other factors are at work to explain possible declines in casualty rates.


Helmet advocacy in context

Along with points 2 – 4 above, there is another fundamental problem with helmet advocacy. As well as short-term risk compensation, there is the question of a longer term adaptation to the wearing of cycle helmets. This is a question of cultural change in which the issue is about the wider meanings of cycle helmet use: why is it assumed that cyclists should consider wearing them in the first place?

These are the group of questions which have been raised by sceptics of helmet advocacy – and not just about compulsion. ( See our posts here for just some). Why should cyclists be expected to wear helmets, and not car occupants, certainly for longer journeys? Wouldn’t it be more sensible and civilised to reduce danger at source, for the benefit of all road users?  If cyclist responsibility is to expected, why shouldn’t this come in the form of supporting responsible cycling behaviour, particularly with regard to pedestrians? Apart from the Safety in Numbers effect, why don’t we look at countries which regard cycling as a normal everyday behaviour – done in normal clothes and rarely in helmets – and have both high levels of cycling and lower casualty rates?  And why, when official “road safety” initiatives are supposed to be based on evidence, should helmet use be pursued with minimal, zero, or even negative effects shown after at least 35 years of helmet advocacy?

These questions build up into an accusation against helmet advocacy – one which explains the bitterness of discussions about helmets. They lead to the conclusion that helmet advocacy is getting hold of the wrong end of the stick, is victim-blaming and a major red herring which draws attention away from what should be done for cyclists’ (and other road users’) safety.


Road safety theory and politics

Ultimately the debate about cycle helmets is of great importance because it draws attention to major issues of safety on the road. Risk compensation suggests that iconic “road safety “initiatives and ideology have:

1.    1.   Transferred risk from the most dangerous to others to those least dangerous to others and most vulnerable, as with seat belts, more crashworthy cars and highway environments more forgiving to careless driving. In the first instance, this may lead to larger numbers of pedestrians – and to some extent cyclists – being hurt or killed as a consequence.

2.     2. Operated on the basis thatwhen the move of pedestrians and cyclists (particularly the young, elderly and disabled) away from the road environment and the resultant reduction of cyclist/pedestrian traffic has led to reduced casualties among these groups, this has been regarded by the “road safety” lobby as progress.

3.     3.  Not accepted that reductions in road deaths related to levels of motorisation have occurred at different times in a variety of different societies irrespective of the kind of official “road safety” interventions that have been applied.

Naturally, “road safety” personnel – whether highway engineers, road safety officers, or doctors, police officers, etc. – are unwilling to fully accept this. Yet most accept the truth of risk compensation to some extent. The debate about helmets inevitably results in discussion about risk compensation, evidence based policy, and the responsibilities of different kinds of road users.

And I would argue that this debate should be pursued, as it leads to a greater understanding of the way safety on the road is thought of. In particular, we need to criticise the “road safety” lobby’s neutralising of the difference between the obligations of those with greatest potential to endanger others and that of those endangered by this behaviour. That is more important than whether individual cyclists wear helmets.

 If that sounds overly political, the fact is that this is political: it deals with the relative destructive power of different groups of road user, as well as the official politics of government. It deals with ideology: however much the evidence needs to be presented, ultimately that has only some effect on people’s behaviour. Ultimately the issue is about culture and what constitutes acceptable behaviour.

And it has to be worked through, for the safety of cyclists and other road users.






4 thoughts on “The effects of New Zealand’s cycle helmet law: The evidence and what it means.

  1. Dr Dorothy L Robinson

    There is also a follow-up article that splits injury rates into collisions with and without motor vehicles involvement –
    “cycling injuries not involving motor vehicles increased dramatically, quadrupling in 15-19 year olds (from 11.6 to 45.9 injuries per million hours) and more than doubling for children (from 39.5 to 85.4 per million hours) and adults (from 15.9 to 32.3 per million hours).”

    The BHRF website provides a link to a study suggesting that “Helmet laws discourage the safest cyclists” – This may be one of the factors at work here. It seems likely that helmet laws have discouraged cycling for transport (often a relatively safe activity). Some people continued cycling, but the much higher injury rate for collisions not involving motor vehicles suggests that many are taking part in risky activities such as mountainbiking.

    1. rdrf Post author

      Thanks for this Dorothy, very interesting. Also it could just be that apart from specific (far) higher risk cycling activities – mountianbiking, cycle racing – there is a general risk comensation/behavioural adaptation effect . Although that would effect cyclists riding in the vciinity of motor vehicles as well.

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