Cognitive Daily

A fascinating press release is starting to gain attention.

Researcher Ian Walker equipped his bike with a precise sensor that measured exactly how much room British drivers gave him when they passed. After tracking thousands of motorists, he was able to make an astonishing claim: when he was wearing a helmet, drivers gave him significantly less room on the road — over 8 centimeters less.

He suspects the reason is that drivers make judgements about the competence of a cyclist based on whether or not he is wearing a helmet. Indeed, Walker was struck by cars twice during the experiment — both times he was wearing a helmet.

In a separate condition, Walker rode the bike wearing a wig so drivers approaching from behind thought he was a woman. Now, he found, drivers gave significantly more room.

So, is it actually safer to ride without a helmet? It’s still difficult to say: helmets would still be safer for accidents that didn’t involve cars, and there may be cultural factors involved as well. Most people who’ve lived in both Britain and the U.S. claim few British riders wear helmets. So British drivers may be making an assumption that U.S. drivers, at least, don’t make. I’d like to see the study replicated in the U.S. to see if the phenomenon is cross-cultural.


  1. #1 Koray
    September 12, 2006

    It says over 8 cm, not inches, in the article. I don’t think drivers believe riders without helmets are less experienced. It is possible that they think those riders are more vulnerable, so they give them ‘extra’ room.

  2. #2 Dave Munger
    September 12, 2006

    Thanks for the correction, Koray, I’ve fixed it.

  3. #3 Chris
    September 12, 2006

    It’s also possible that even if your risk of accident is higher with a helmet, your risk of serious injury is lower (because fewer of your accidents result in serious injuries – that’s what the helmet is for, after all). So it’s not really “safer” to ride without a helmet even if you have fewer accidents, because the accidents you DO have are more dangerous accidents.

  4. #4 Sharon
    September 13, 2006

    Chris, it’s also possible to come to the opposite conclusion. We really don’t know which is a worse risk on balance: the risk of more serious head injuries without wearing a helmet, or the risk of having more accidents if helmet-wearing.

    As well as the distance factor measured by Ian Walker, you’ve also got other factors, such as helmets making heads a bigger impact target, risk compensation, and other issues like whether helmets affect the visibility of cyclists. It’s not easy to tell whether helmets make the wearer safer, but there’s a fair bit of evidence to suggest that they don’t.

    Personally, as a British cyclist for more than a quarter of a century, I don’t buy that “non-helmeted cyclists are less competent” explanation, it seems to me that it’s more likely to be something different, a sort of “that cyclist is a nutter for not wearing a helmet and they are more vulnerable (Koray’s point) so I’d better give them more room”.

    One reason for my belief is the best treatment I ever used to get at the hands of car drivers, when they would regularly give me at least six feet of room. This situation would occur on a particular main road, at night, pitch black (no streetlights). From all the comments I received from “friends”, they thought I was a nutter for cycling along that road late at night, even with a powerful lamp on my bike. They thought it was very foolhardy. So I’m convinced that if a driver thinks you’re a nutter he/she will give you more room. It was a great road, that road. It was long and straight and for all but two spots on it, had excellent visibility. Drivers could see you 500 yds away, the road was wide enough for everyone. For some reason my “friends” all thought I should instead cycle not on the main road, but on a quiet winding road parallel to the main one. For some reason they couldn’t get it through their heads that drivers tend to race along the quiet roads, and they don’t expect to see cyclists on the road (because it’s quiet) and so a winding quiet road with a speeding driver is not a good thing for the cyclist also using the road! They didn’t seem to get that I’d be putting myself at higher risk that way.

    Some people recommend, if you need a little more room on the road, cycling in a slightly wobbly fashion in advance of a car’s approach, as it reminds them to leave plenty of room.

    I’ve never been hit by a car yet, but there have been plenty of occasions when a car driver thinks it’s appropriate to pass fast giving me less than 6 inches of room, rather than the recommended 6 feet.

    There you go, cognitive psychology people, if you want to do a series about how people have their ideas of risks totally messed up and how visuals can make weird differences to behaviour, then try cycling! It’s all in there!

  5. #5 Robert
    September 13, 2006

    If the hypothesized helmet effect was because the driver thought the rider was less experienced, an interesting follow-up experiment would have the rider on a racing bike and wearing pro cycling togs.

    Note that of the variables tested, they rank in order:
    1. Big vehicles (e.g., buses and heavy trucks) pass closer than small ones.
    2. Drivers give women a wider berth than men.
    3. Riding farther out into the lane leads to smaller margins.
    4. Helmets.

    Or, actually, wrt #2, drivers give a guy wearing a wig a wider berth — not that there’s anything wrong with that.

  6. #6 swivel-chair
    September 13, 2006

    Just going by the press release, there seem to be a couple serious limits to the study. (1) 3 inches (8 cm) closer in an average distance of 4’4″ away doesn’t seem like very much, even over 2,500 measurements. I guess I’d like to see more of the data. (2) It wasn’t a double-blind study. Walker (as subject) knew when he was wearing a helmet. He may very well have been riding differently when he was helmetless. Also, Walker as researcher knew, when he was setting up the equipment & processing the data, which condition his subject was about to be in or had just been in, allowing the possibility that unconscious bias could creep in.

  7. #7 Jamie
    September 13, 2006

    There is the distinct posibility that drivers steered away from the woman with the abnormaly large head I know I would.

  8. #8 Dave Munger
    September 13, 2006

    “Just going by the press release, there seem to be a couple serious limits to the study. (1) 3 inches (8 cm) closer in an average distance of 4’4″ away doesn’t seem like very much, even over 2,500 measurements. I guess I’d like to see more of the data.”

    You’re right on both counts. The 3 inches could be achieved by every car going 3 inches closer, but it could also be achieved by every 12th car going 3 feet closer. Obviously the second scenario is much more dangerous than the first.

  9. #9 Dave S.
    September 13, 2006

    After reading this I was reminded of an interesting factoid I heard recently. Apparently, it is more dangerous for a pedestrian to cross at a marked crosswalk than at an unmarked one, possibly because the pedestrian puts too much confidence in the markings to stop a motorist (although the linked study suggests that explanation may be somewhat dubious). Not sure if this has anything to do with the current discussion, just thought I’d put it out there.

  10. #10 Ormond Otvos
    September 13, 2006

    I see a market here for a helmet with a wig exterior. Really.

  11. #11 macrobe
    September 14, 2006

    This reminds me of a claim by a representative of a motorcyclist’s organization that wearing a helmet was dangerous because of possible asphyxiation. As a scientist and a motorcyclist, I prefer to decrease the probabilities and degree of injury by wearing a helmet on any two wheels.
    Now, a wig on a helmet……..

  12. #12 Kenny
    September 14, 2006

    Dave S.


    I used to live right in front of a crosswalk. There was an incident of screetching tires about once a day, on average.

  13. #13 Stephen
    September 15, 2006

    I know someone who cycles to work because, er, he’s such a bad driver that his insurance company told him not to drive.

    So, one day he arrives at work without a helmet.

    Where’s your helmet?

    Oh, it broke in half.


    I went over a railroad track, and my front tire wedged, and I went flying over the handlebars. But, I had a soft landing – on my head. I’ll get another helmet from the bike shop at lunch.


  14. #14 Saskia
    September 19, 2006

    Mmm, I see an interesting line of research here. Would this effect be cross-cultural? I wouldn’t mind spending some time cycling across different countries all over the world to find out…

  15. #15 Jim Davies
    October 25, 2006

    Check out

    It seems pretty clear to me that, because of risk compensation, wearing a bike helmet increases your chance of injury and serious injury.

    Read wikipedia on risk compensation to see how it affects seatbelts and football helmets. Fascinating stuff.

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