Mandatory bicycle helmets: does correlation mean causation?

Percent of total trips by bicycle (data from Pucher & Buehler, 2008)

It’s evident from the response to my article two weeks ago (Is the mandatory helmet debate a distraction?), that some people still see compulsory helmets as one of the major obstacles, perhaps even the main obstacle, to significantly higher uptake of cycling in Australia. So I want to look at the main arguments for repealing the compulsory helmet law.

As I’ve said before, I accept that mandating helmets in the early 90s was arguable policy, at least in the case of adults. If it were proposed for the first time today, I doubt it would get up (except for children). So I don’t think those who advocate repeal are necessarily “wrong”.

But in my view the helmet law is not the main thing holding cycling back in this country – it doesn’t even come close. And since it’s got virtually no traction politically, it’s also a waste of energy. Ultimately it distracts from the key issue – the danger, whether perceived or real, of cycling in traffic.

A key argument made by many repeal advocates is that countries without mandatory helmet laws have high bicycle use. Australia, in contrast, has both low mode share and draconian helmet laws; ipso facto, they say, mandatory helmet laws are the key problem.

What I think is happening here is the familiar problem of confusing correlation with causation.

There’s no doubt bicycle use in Australia is indeed low compared to some other countries. For example, according to Pucher and Buehler in Making cycling irresistible: lessons from the Netherlands, Denmark and Germany, bicycles capture 27% of all trips in the Netherlands and 18% in Denmark, but a mere 1% in Australia (see exhibit). And there’s no doubt helmets aren’t considered important in these countries – in the Netherlands, for example, less than 1% of adults and only 3-5% of children choose to wear a helmet when cycling.

But does the law on helmets explain why cycling is so much more popular in these countries than it is in Australia?

The first thing the repeal advocates should ask themselves is this: why are only 1% of trips in the UK taken by bicycle even though helmets aren’t mandatory in that country? That’s no better than here! Or why is cycling’s mode share only slightly better in Ireland and Canada than it is in Australia, even though these two countries don’t have mandatory helmet laws? Clearly, whatever the explanation is for the comparatively low rates of cycling in these countries, it has nothing to do with any compulsion to wear a helmet.

They should also ask themselves why there are such enormous differences between countries where helmets aren’t mandatory. The fact that bicycle use is more than twice as high in the Netherlands as it is in Germany – and nine times higher than it is in France and Italy – suggests pretty clearly that there are other highly influential factors affecting the propensity to cycle that have absolutely nothing to do with helmets.

Helmet policy doesn’t explain why bicycles capture 34% of trips in Munster, but 13% in Munich. Or why the corresponding figure for Groningen is 37% compared to 10% in Heerlen; or 20% in Bruges but 5% in Brussells; or 19% in Salzburg but 3% in Wien. Read the rest of this entry »


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