When I was in the U.K. doing radio interviews for Traffic, I would often get asked if wearing cycle helmets actually made things less safe for cyclists. This happened primarily because the book features rather striking research by Ian Walker, a traffic psychologist at the University of Bath, and this was mentioned in the press kit.

To briefly summarize, in his study (published as “Drivers overtaking bicyclists: Objective data on the effects of riding position, helmet use, vehicle type and apparent gender,” in the journal Accident Analysis and Prevention), Walker outfitted a bike with a device that measured the distance of passing cars. He found, among other things, that drivers tended to pass more closely when he was wearing a helmet than when not (he was struck by vehicles twice, both while wearing a helmet).

This was a surprising, somewhat controversial finding that generated a lot of news coverage. To my mind, Walker’s findings were more interesting for what they said about interpersonal psychology on the road than safety itself; mostly because I felt, and Walker seems to agree, that the primary question of bicycle safety had less to do with the helmet than other factors. As the above photo suggests, cyclists in places like Copenhagen or Amsterdam very rarely wear helmets, and yet they enjoy a much safer ride than in places (like the U.S.) where helmet-wearing seems more ingrained. The argument is often made that those places have protected cycle lanes and the like — though the photo also shows that is not always the case.

But to return to the radio interviews, I often found myself getting frustrated because the radio journalists seemed to want a handy “takeaway” answer: Well, do helmets make cyclists safer or not? The problem was, I really didn’t know (disclaimer: I do wear one, rather out of habit and without much thought other than a fear of New York City streets).

This was a problem I had in trying to give many answers relating to traffic — there are often an endless series of “on the other hand” qualifiers. As with any kind of epidemiological inquiry, traffic presents such a complex system, with so many interacting variables (e.g., do helmets make drivers act less safe) and “confounding factors” and incomplete data sets, that coming up with easy answers is impossible: and anyone who seems to have easy answers probably doesn’t know what they’re talking about. One favorite example of this for me is the nutmeg you hear drivers say, with deeply held conviction: ‘Well I’ve heard it’s not speed itself that’s the problem, it’s differences in speed.’ This is a statement that is true — except when it isn’t. It lacks context, it lacks explanatory power. We would do as well, if not better, to note that every traffic fatality/injury involves speed: If the car wasn’t moving, no one would have died/been injured.

But I was curious as to how Ian Walker, after putting his research into the world and subsequently being asked these sorts of questions, undergoing these sorts of debates, ultimately felt himself about what his findings (at least on several stretches on English roads) had revealed.

Over to you, Dr. Walker:

“The apparently simple query ‘Do bicycle helmets work?’ turns out to be the most complex question I have ever encountered. Since I published my own small contribution to the nightmarish tangle of helmet research a couple of years ago, I have read and answered hundreds of emails on the subject from interested – in both senses of the word – people. I am grateful to Tom for giving me this chance to summarize a few of my disjointed thoughts on the matter.

First, let me deal with this matter of interest: I have none. I do not make bicycle helmets, nor do I sell them, and nor do I have anything to gain from their demise. It really doesn’t matter to me one way or the other if they ‘work’. I am a scientist, and what interests me is getting at the truth, whatever that is. This leads me straight onto the big issue: I do not know whether or not bicycle helmets save lives. And, critically, nor does anybody else.

The reason nobody knows for certain is that only one method exists for us to get a definitive answer: the experiment. If we took a large number of bicyclists and randomly made one-third ride with helmets, one-third ride with fake helmets (the placebo) and one-third ride with no helmets (the control), then after a couple of years we could count the dead and get the answer we are hoping for. Sadly, however, there are some fairly obvious ethical difficulties with this plan!

So all the evidence we will ever have on this matter is indirect: casualty figures, surveys and observational studies, all of which are riddled with biases. And for every piece of evidence we can find in one direction, there is another telling us the opposite. Let me outline just a few of the many reasons why the topic is so complex.

First, I am not going to deny that putting some padding on your head will absorb some energy in an impact. It would be crazy to suggest otherwise. The actual amount of energy absorbed is almost certainly smaller than you think, but the fact is there has to be some cushioning: if a particularly weird kidnapper made it clear I had absolutely no alternative but to be hit on the head with a hammer, I would definitely choose to wear a bicycle helmet rather than go bareheaded. This all leads us to the ‘common sense’ position which at one extreme says ‘obviously’ helmets are useful and which, at its most conservative, would say it ‘cannot hurt’ to wear a helmet.

The difficulty with this position is twofold. First, even if a helmet absorbs a lot of energy in an impact, this benefit might be cancelled out by the helmet making the impact more likely in the first place. If you have read Tom’s excellent book, you will be familiar with the idea that people might adapt their behaviour to take more risks whenever they start to feel safer. We have no hard evidence on this, but it is plausible, given what we have seen elsewhere in traffic, that helmets make riders feel safer and they respond to this by taking more chances. And even if the riders don’t change their behaviour, my research showed the drivers with whom they share the road certainly change theirs: whenever I put a helmet on, other things being equal, drivers got measurably closer as they passed my bicycle. This will almost certainly translate into a higher likelihood of accidents across large numbers of people.

The second issue with the ‘common sense’ position is this: if helmets do work, why is this proving so difficult to see? In countries where helmets have been made mandatory, and where usage went from low to high levels almost overnight, there is just no real evidence of a concomitant drop in injuries. Indeed, what we see instead is a big drop in the number of people cycling, which is a disaster – far worse for public health than the few head injuries the helmet laws tried to prevent. Whenever a person gives up cycling, they get far less day-to-day exercise. This means they trade a very small risk of dying from a head injury (almost certainly smaller than you think – I can almost guarantee it won’t be a bicycling head injury that sees you off) for a greatly increased risk of dying early from heart disease or cancer (almost certainly larger than you think – I’d lay good odds that one of these two will get you).

Matters are further complicated in other ways. It is possible to find evidence from hospital records suggesting bicyclists who wear helmets hurt themselves less often. But it is equally possible to find evidence that bicyclists who wear helmets ride more cautiously, and are much less likely to mix with motorized traffic – which is where most of the danger comes from in the first place.

These have just been the headlines. There are any number of other complexities which further muddy these waters, but I won’t go into them for fear of taking over Tom’s whole blog. Instead, I will exploit his generosity another way, by using this platform to get something off my chest. Here are two comments I have heard – quite seriously – dozens of times. They are comments which, as an evidenced-based researcher, I would be happy never to hear again:

1. “I crashed my bike and afterwards the helmet had shattered into several pieces. This proves it saved my life.” It is the illogic that riles me here. If you don’t see the problem, replace the word ‘helmet’ with ‘egg’. Just because the helmet was broken after a crash, this tells us very little. I know what people mean to say, of course – they are trying to say ‘the helmet must have taken the blow’, but this pre-supposes too much about how well helmets are able to do this. Plus, as many motorcycle helmet engineers will tell you: if it cracks, it’s failed.

2. “After the crash, all the paramedics, doctors and nurses told me the helmet had saved my life.” Did they? Did they really? I do hope not, because what evidence did they base that statement on? Did they make the hapless bicyclist crash again in exactly the same circumstances, this time sans helmet, to confirm they would die bareheaded? Bah! The medical profession is seen by most laypeople as the paragon of science, but in reality it has its fair share of prejudices and orthodoxy. One of these is the fixed belief, de-spite the complexity of the evidence, that wearing a helmet must be a good thing. I really would like to believe the following tale, which someone once related to me, is genuine. A bicyclist visited their doctor with a damaged knee following a crash. “You should have been wearing a helmet,” says the doctor sternly. “How would that have saved my knee?” replies the cyclist.

So to sum up, nobody knows for certain whether bicycle helmets work, overall, to protect bicyclists. They must absorb some amount of energy in a collision, and although I’m not sure how much of the energy they touch from a 2-ton car, even if they removed a lot of it, there are plausible ways in which that benefit gets cancelled out by helmets making accidents more likely in the first place. Most bicyclists who die with head injuries also have fatal chest injuries too.

I’d always recommend helmets for children, whose accidents are slow-speed falls in the absence of traffic. But for adults, who travel at higher speeds, often in the presence of motor vehicles, we will never have a 100% reliable answer about whether they decrease or increase risk. In the interests of full disclosure, I very rarely wear a helmet myself. What you do is your own decision. Just make that decision is based on your reading of the evidence rather than guesswork, that’s all I’m asking.

And finally, having said all that, I would like to suggest that this is all the wrong question to be asking anyway. Nearly all of the serious danger to bicyclists comes from drivers. Instead of fretting about the utility of helmets after collisions happen, bicyclists should be focusing on the careless or reckless driving that causes those collisions in the first place. Consider burglary for a moment: I would suggest the prime responsibility for this social ill lies with the burglars who choose to perpetrate it rather than the householders who are the victims. I can’t help feeling bicyclists are in a very similar position when they allow themselves (ourselves!) to get drawn into this debate.”

Ian Walker

This entry was posted on Wednesday, October 1st, 2008 at 4:01 pm and is filed under Bicycles, Cyclists, Risk, Roads, Traffic Culture, Traffic Psychology. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.