Putting a lid on the debate: mandatory helmet laws reduce head injuries

A re-analysis of the data shows there’s a good case for keeping helmet laws.

Since mandatory bike helmet laws were introduced in 1991, researchers, cyclists and campaigners have debated the law’s role in cyclist safety and the desirability of bike riding.

A new analysis reveals rates of head injuries reduced by almost a third after the laws were introduced. We spoke with the lead author of the study Jake Olivier, Senior Lecturer at UNSW’s Prince of Wales Clinical School, about the evidence used in the bike helmet debate:

My involvement in this research began when the Voukelatos and Rissel paper came out last year in the Journal of the Australasian College of Road Safety. The paper said rates of cyclist head injury had decreased more in the period before the mandatory helmet laws were introduced than after.

When I read it initially, I thought the article had some interesting methods. But on closer inspection, the authors’ analysis looked weak.

It came out later that there were some data errors, which were pointed out by Tim Churches. The errors turned out to be real and Voukelatos and Rissel were given a chance to respond. They didn’t, so the journal retracted the paper.

At that stage, I decided to take Voukelatos and Rissel’s basic idea and do a more comprehensive and statistically rigorous analysis.

What was your methodology?

In order to find out whether there was a reduction in head injures, we looked at the ratio of head to arm injuries – and this is what Voukelatos and Rissel did.

Any major drop in cycling rates would have resulted in a drop in head and arm injury rates. So the comparisons we made were “exposure free”, meaning the variations in cycling numbers wouldn’t affect the analysis.

What periods and regions did you examine?

We looked at data from New South Wales from eighteen months before the legislation and then eighteen months after its introduction. It’s the same data source that Voukelatos and Rissel used. (The Daily Telegraph ran a story today saying it was new data but this isn’t true).

When Tim Churches corrected the mistakes from Voukelatos and Rissel’s paper, he came to the same conclusions we did.

What are the key findings from your re-examination of the data?

We found a 29% reduction in bicycle-related head injury attributable to the introduction of the mandatory helmet law.

There has been some debate about whether the head-to-arm injury ratio was the best methodology. So we also looked at the ratio of head to leg injury, to see if we could observe the same effect among cyclists, and we did.

We then repeated those two analyses on pedestrians. The helmet law was directed at cyclists not pedestrians, so if we found a big drop in pedestrians, that would be an indication of general road safety improvements.

But we did not see a reduction in pedestrian head injury at all relative to limb injuries.

So the reduction in head injuries seems to have been isolated to cyclists and that drop appears to be real.

How does your analysis compare with the existing data on the introduction of mandatory bike helmet laws?

There are some conflicting reports out there. And a lot of these have been dogged by problems of confounding variables: Is the decline in head injury a result of general road safety improvements? Is it because of other things that are happening in the community?

We developed our analysis to account for all that – and this sets our methodology apart from what’s been done in the past.

Based on our analysis, I think the question of whether mandatory helmet laws reduced head injury should no longer be debatable in NSW. We should maintain mandatory helmet laws.

Did cyclist numbers reduce after the mandatory helmet laws were introduced?

The Roads and Traffic Authority (RTA) commissioned a few reports around the time the helmet law was introduced. One that came out in 1991 found the number of child cyclists reduced by around a third but there seemed to be an increase in adult riders. The overall numbers appear stable around that time.

So the numbers of cyclists overall may not have changed much, with more adults cycling but fewer children cycling – our model accounted for that.

Our conclusions remain the same regardless of the numbers of cyclists. But there is certainly active debate about whether it stopped people from cycling or not, and whether those that stopped cycling took up other activities and returned to cycling after our study period.

Are helmets currently a barrier to cycling?

Helmets aren’t a major barrier. There’s a widely cited survey by the Cycling Promotion Fund and the National Heart Foundation that suggests it is one of many coming in as the tenth most selected barrier. However, there were some problems with their methodology in terms of finding the primary barriers to cycling.

The researchers asked, “What do you find are the barriers to cycling?” and gave the respondents a list of choices, allowing them to tick as many as they wanted. The problem with that is you don’t get an idea of what the main barrier of cycling is for these people.

The results showed around 16% said the helmet law was a barrier to cycling and it was ranked the tenth most common barrier. So when you consider that this might not be the main barrier, the actual figure is likely to be much lower than 16%.

How can we improve cycling rates?

We need to separate cyclists from pedestrians and motorcars, increase education programs and work to make the roads safer in general.

If we can increase cycling numbers in Australia we will get a “safety in numbers” benefit, but we are far from reaching cycling participation rates to achieve that.

Improving road infrastructure for cyclists would certainly increase safety. But on top of that, we need to make sure every rider has a helmet on top of her head to get the maximum safety benefit.


The Conversation has previously published articles on both sides of the mandatory bike helmet debate: Chris Rissel argued ditching bike helmet laws would encourage more people to cycle and the public health benefits would outweigh the increased risk of head injury and Max Carmon outlined the benefits of mandatory helmet laws in protecting cyclists against head trauma.