Would a helmet help if hit by a car?

This post is part of a series: it starts with the intro to the helmets issue, then the summary of the best evidence on helmets, then a quick diversion into how dangerous cycling is and an attempt to define terms. And there’s more…

Brake, the “Road Safety” charity, say yes:

Helmets are effective for cyclists of all ages, in crashes which do and do not involve another vehicle.

That matters, because if cycling safety is in the news, journalists will go to Brake for an easy quote.

The British Medical Association also say yes:

Helmets provide equal level of protection from cars (69%) compared to other causes (65%)

This is important, because the BMA is a highly trusted organisation with political influence, and their current policy is to endorse the criminalisation of riding a bicycle when not wearing a helmet.

Interestingly, president of the Automobile Association Edmund King, who was giving away free advertising bicycle helmets in London this week, disagrees with the nation’s medics on both issues:

We don’t think helmets should be compulsory but we think there are benefits… Our view is that helmets do not protect against cars but they may protect against some of the 2.2m potholes which often are the cause of smashes into the ground by cyclists.

Carlton Reid adds a little detail:

Most bicycle helmets are designed for falls to the ground from one metre at speeds of 12mph. They offer almost zero protection in collisions between bicycles and fast-moving cars.

The risk reduction provided by helmets in bicycle crashes that do and do not involve motor vehicles is one of the few sub-group analyses that was performed in the case-control studies that are covered by the Cochrane Review, and it’s no surprise that this is the source for the BMA’s claim. In bicycle hospitalisations that did not involve cars it reported nearly 70% fewer head injuries in the helmet wearers. In bicycle hospitalisations that did involve motor vehicles there were nearly 70% fewer head injuries in helmet wearers.  A helmet is equally effective at preventing head and brain injury in crashes with cars as in solo crashes.

What makes Edmund King and Carlton Reid think they know better than the nation’s medics and road safety campaigners?  Indeed, what makes them think that they can go around claiming the opposite of the cold hard corroborated stats of the Cochrane review?

Well actually, they’re not. Not quite. King and Reid are judging helmet efficacy by a slightly different metric to the Cochrane Review.  The Cochrane Review is the looking at the set of bicyclists who have had an accident of a severity that hospitalises but does not kill outright.  The review says nothing about deaths, for example, and as the Cochrane Review itself notes, more than 90% of cyclist deaths are caused by “collisions” involving moving motor vehicles (the same proportion is found again by a separate route in the TRL review and again in NYC).  But only 25% of hospitalisations were caused by motor vehicles.  And while Cochrane suggested a whopping 85% of head injury hospitalisations (which in turn account for around half of all cyclist hospitalisations) could be avoided by wearing a helmet, the TRL review of post-mortem reports found that only 10-16% of all cyclist deaths might have been avoided.  Hospitalisations, of the sort reviewed by Cochrane, are not representative of deaths.  Fall off your bicycle and you might get hurt.  Get hit by a car and you might die.

That’s because when you fall off your bicycle, chances are you are toppling over some way — precisely the sort of simple fall that a helmet is designed for, and the sort of fall that is least likely to cause life-threatening injury to any other part of the body.  When hit by a car the body might be crushed, or thrown up and around at speeds that helmets are not designed for, and so there are many more opportunities to suffer fatal trauma to other parts of the body.

(As an aside, Brake actually get this one the wrong way ’round:

Nearly 50% of cyclist admissions to hospital are for head and facial injuries, and the majority of cyclist deaths and injuries are a result of head injury.

TRL has the answer to this one: around three quarters of cyclist fatalities did indeed involve a serious head injury.  But only about a quarter involved only a serious head injury.  The rest also involved one or more additional life-threatening injury.  The Brake claim is at best misleading.)

This doesn’t mean that the BMA and Brake are all wrong* and King and Reid are completely correct.  A car at speed may be able to cause the sort of multiple trauma that merely falling over doesn’t, but that doesn’t mean that cars aren’t also capable of causing the sort of crashes that helmets are designed for, especially in low speed city traffic.

So Edmund King is wrong**.  But within the untruth he is communicating an important truth: cars are responsible for the most serious injuries and death, and helmets will rarely help in those cases.

Brake and the BMA are correct.  But their strictly truthful statements hide the crucial details, without which they are liable to seriously mislead.

* Indeed, they can’t be wrong.  You can provide a hypothesis for why helmets might be useless in crashes with cars, but no hypothesis can trump the real world stats that say helmets are useful in crashes with cars.

** Carlton Reid is not wrong, because he specified fast-moving cars.

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18 responses to “Would a helmet help if hit by a car?

  1. “That’s because when you fall off your bicycle, chances are you are toppling over some way — precisely the sort of simple fall that a helmet is designed for, and the sort of fall that is least likely to cause life-threatening injury to any other part of the body.”

    If you are toppling over in some way, I would have thought your head would be the last thing to hit the ground, if at all. Your body would instinctively stop it. I wonder whether that has ever been tested.

  2. The potholes are an interesting case, especially here in the US, where many towns and cities economize on road maintenance. I have become a huge fan of huge slick tires (2 inches or larger) because they seem to reduce the effects of riding on horrible roads.

  3. If your aim was to show that the science can be confusing and misleading (misleading, that is, if you haven’t covered the science from all angles) then I think you have succeeded.

    So far, I haven’t seen anything to suggest either way that helmet wearing should be vigorously encouraged or even made compulsory, unless of course you do the same for walking, driving a car, climbing ladders or going to the pub.

    It makes me wonder about front, and then rear, seat belts in cars, and motorcycle helmets. Was the evidence for those clear-cut, or could one make the same arguments about them, eg while a seat belt greatly reduces injury in a crash, the probability of a crash is still very low?

    I recall that all of these were vigorously opposed, particularly by those of a libertarian disposition which usually means conservatives, with either a small or a big “C”. They all went through in the end.

    And they didn’t discourage people from driving or biking, but there the similarity probably ends. If we label cycling as something which requires people to wear protective clothing and high-vis, a bit like rock-climbing or potholing, potential cyclists are bound to be turned off en masse. Whatever the advocates may say, compulsory cycle helmet laws have co-incided with (which doesn’t automatically mean were the cause of) significant declines in cycling and rises in diet/exercise-related conditions.

  4. Pingback: AWWTM: Would a helmet help if hit by a car? | Joe D

  5. Would a helmet help if hit by a car?
    Most likely NOT. A helmet is designed to protect the top half of the skull, protecting the brain. It won’t save your face. Or your neck, your spine, your limbs or your torso…
    I’ve known motorcyclists who’ve been driven over, who’ve been catapulted into walls and road furniture, who are disabled from even low-speed tumbles- in fact there’s a specific ‘biker’ injury where a falling rider has nerves in their shoulder severed by the way their body pivots about the outstretched arm as they fall.
    In fact, the only thing that seperates motorcyclists and bicyclists is the relative speed they travel at. Both groups are regarded as third class citizens by four (or more)-wheeled motorists.

    Are helmets useful? Yes. You can beat a driver to death with one.

  6. Helmets vary… I think “skate” type ones are way better then the areo bunch of bananas sort and in any case many are ill fitted thereby reducing any benefit. Judging their effectiveness is all well and good but is also rather irrelevant… here’s why…

    One could tape a kipper to one’s forehead and no doubt it would provide some measure of protection. The question is, does riding down to the shops carry a high enough risk of head injury to warrant wearing armour of any sort? The answer is clearly “no” so the effectiveness of helmets is not an issue for normal cycling. Downhill slalom mountain biking on the other hand…

    Judging risk is part of life. Learning to deal with it makes you safer. How about “road crossing helmets” or “bath lids”? I am informed that the group with the highest risk of head injury is pedestrians over the age of 60…. “pensioner hat” anyone?

    If you think you are likely to fall and hit your head, you should wear a helmet… you judge.

    -L

  7. Thanks for a nice “balanced approach” to this theme.
    However, I am sorry but I do not follow you logic here :

    You can provide a hypothesis for why helmets might be useless in crashes with cars, but no hypothesis can trump the real world stats that say helmets are useful in crashes with cars.

    Real world stats can be deceptive as you have just shown. Right ?
    Which stats by the way ?

    ~~~~
    ( I am not an editor of cyclehelmets.org, but I keep in close contact with some of the editors. Sober critique of the content is appreciated. Do let the stuff sink for a few days though, and make sure you notice how the “other” side is not silenced or grossly misrepresented, unlike in the material from the pro-compulsionists )

  8. It’s worth reading what Rune Elvik has to say on the Cochrane Review. It bears out much of the criticism there has been of case control studies on helmet use on cyclehelmets.org.

    I would echo Morten Lange’s comments: where are the statistics that show helmets to be effective in crashes with cars?

  9. Thanks everyone!

    “Balanced approach”? Gosh, I hope not ;) I wouldn’t want to be guilty of the journalist’s idea of being “fair”. I’m trying to find the best — or least worst — evidence on the issue, not politely present the arguments of opposing sides. That happens to be a bit complicated given that none of the evience we have is overwhelmingly compelling.

    “I would echo Morten Lange’s comments: where are the statistics that show helmets to be effective in crashes with cars?”

    Er. That’s what this post (when read alongside the previous “so what’s the best evidence?” post) is about! (I thought it was clear, but then, when you’ve been buried in biomedical literature for enough years you start saying things that make perfect sense in your own little world, but mean nothing to the average person.)

    The case-control studies reviewed in Cochrane showed equally strong protective effects in solo and with-vehicle crashes. This post reiterates the limitations of that study — including why these stats only apply to people involved in a crash severe enough to hospitalise, and can’t be applied to the set of crashes where the cyclist is killed outright.

    To reword the original post: there is a hypothesis that helmets protect you in crashes with cars. It is supported by stats (Cochrane) in the case of crashes of a severity to hospitalise. It is poorly tested in cases of crashes of a severity to kill (TRL). There is a hypothesis that helmets do NOT protect you in crashes with cars. There is a hypothetical mechanism to explain why this second hypothesis might be true. But is contradicted by the stats in hospitalisations, and poorly tested in the deaths.

    There are reasons to be wary of the stats, and I hope I’ve explained many of those, but scientists and doctors and public health types, fully aware of the limitations of case-control studies and the questions that they ask, will always take the stats over a mere hypothesis. I can’t fault them for doing so. (Though I can fault them for promoting legislation on such limited evidence.)

    There is of course much more to cover, and many of the commenters here are way ahead of me! I’ve been in the saddle since Tuesday and haven’t had time to work through the rest of this series. Normal service will resume when this lovely weather goes away.

  10. There are so many what-ifs. My girlfriend, an experienced cyclist, was cycling up a road at around 5MPH, turned and fell off. The coroner said she would almost certainly have survived if she had been wearing a helmet and from my viewpoint 30 yards down the road it looked relatively trivial. In the following months I read of an ice skater who fell backwards on her head and a man who was punched in a supermarket checkout, both landed on the back of their heads and both died.

    It could be argued, on this basis, we should all wear helmets for any activity but that would be absurd. I will always wear one to cycle, seeing others without helmets makes me run cold but then that’s just down to my personal trauma. Last time I went ice-skating following the accident I was petrified, despite having skated since childhood. I would never cycle, ice skate or roller skate without a helmet but would consider myself extremely unlucky, as Anne was, to die from a fall in my normal day to day activity.

  11. Sorry, I had assumed that pointing out the limitations of the evidence would have lead to you to reject the hypothesis that helmets protect in crashes with cars.

    There is very harsh criticism of the Cochrane reviews value by those who are sceptical of the value of helmets. This isn’t mentioned in your original post on the subject. The authors of the Cochrane Review account for 6 of the 9 papers selected. Isn’t that a little strange? There’s even a spelling mistake on p. 7 (not that that should discount it as research…) All of the selected studies are at least 15 years old, many over 20. Are they seriously suggesting that there are no other worthwhile pieces of research out there?

    Whatever, enjoy the sun – bare-headed, or otherwise!

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  14. –Carlton Reid adds a little detail:

    Most bicycle helmets are designed for falls to the ground from one metre at speeds of 12mph. They offer almost zero protection in collisions between bicycles and fast-moving cars.–

    I’ve seen something similar said many times (though usually it’s 1.5m).

    This isn’t true. Helmets in Europe are certified for a stationary fall of 1.5m: which means the head is travelling at 12mph on impact. Hence the 12mph. It isn’t a fall of 1.5m from a bike travelling at 12mph; it’s a fall of 1.5m from a bike that isn’t actually moving.

    (The actual test involves putting a 5kg headform into the helmet and letting it fall onto an anvils of different shapes from a height of 1.5m.)

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