More news from Dr Ian Walker of the University of Bath, who previously warned us that the white van man passes cyclists closer than other types of motorist. Dr Walker has also collected data showing that

drivers tend to pass closer when overtaking cyclists wearing helmets than those who are bare-headed.

The upshot being that helmet-wearing increases the risk of cyclists being involved in collisions with overtaking vehicles.

Dr Walker thinks the reason drivers give less room to cyclists wearing helmets is because they see them as "Lycra-clad street warriors" and believe they are more predictable than those without.

It's an interesting finding, but let's not forget that, unlike the UK (where this study was done), helmet-wearing is both compulsory and pretty much the norm here in Australia. So on our streets merely wearing a helmet doesn't signal anything about the competence of any given cyclist, and certainly doesn't indicate that anyone is a "street warrior".

Risk compensation?

But it is attractive to speculate on how the theory of risk compensation kicks in here. In brief this means that anything that makes cyclists feel safer may lead them to ride with less caution. And conversely, anything that appears to make a cyclist less vulnerable may change the behaviour of the motorist. To put it even more crudely, a cyclist wearing a helmet appears to be quantitively safer than one going bare-headed, so I (as the driver) may not feel the need to be quite as careful around him/her.

This can also be seen in The Effect of Cycle Lanes on Cyclists' Road Space, a small study by the Warrington Cycle Campaign, which found that motorists tend to give less space when overtaking a cyclist travelling in a 1.5m cycle lane compared to overtaking a cyclist travelling in the general traffic lane.

Image from the Warrington Study

They pose three possible explanations:

  1. Drivers understandably tend to assume that the cycle lane represents an adequate amount of space for the cyclist, so position their vehicles according to the lane markings rather than relative to the position of the cyclist.

  2. Drivers see less need to take special care when overtaking if the vehicle they are overtaking is in a separate lane.

  3. The presence of the cycle lane on the opposite side of the road forces oncoming vehicles nearer to the centre line. This reduces the space available for overtaking vehicles to move to the right.

The first two are certainly consistent with risk compensation.

Ignoring compulsion

I wonder if there could be a reverse effect in jurisdictions where wearing bike helmets is compulsory and normalised. That is, where a cyclist flagrantly ignores the road rules and increases their risk of injury by going helmet-less, would a motorist be less inclined to give elbow-room to the cyclist? "Why should I bother if that idiot doesn't care for his own safety?"

I think this is unlikely but worthy of consideration.

Rug doctor

Returning to Dr Walker's research, he added a further variable and

donned a long wig to see whether there was any difference in passing distance when drivers thought they were overtaking what appeared to be a female cyclist.

While wearing the wig, drivers gave him an average of 14cm more space when passing.

Another interesting finding, but he's yet to test any hypotheses about it. (Just in passing, I would note that the photos in the Warrington Study appear to show a bare-headed female cyclist with shoulder length hair.)

Anyway it's all very intriguing, but not enough in my mind to baldly declare that wearing a helmet inherently makes a cyclist less safe. I don't think we've heard the last of this sort of research, and frankly I can't wait to see more of it.

Update 20 September

Some interesting commentary can be found on the Kent's Bike Blog.
[via monkey martian]

And a nice short rebuttal found in Bicycle Helmet Safety Institute points out that many bike accidents do not involve cars.