Helmets and driver psychology

Ian Walker, a researcher at the University of Bath, has uncovered an unfortunate tendency in human psychology. Drivers are more likely to hit cyclists who are wearing helmets. The hypothesis is that they compensate for the sight of a bare head by giving a wider berth when passing. On average, they gave a cyclist with a helmet 8.5cm (3.5″) less space. This was confirmed observationally by Walker himself, who used a sensor to evaluate 2,500 such incidents in Salisbury and Bristol. Motorists were most cautious around him when we wore a female wig and no helmet. Wearing the wig earned another 14cm (5.5″) of clearance, on average.

The study also found that larger vehicles are more likely to cut it close: “The average car passed 1.33 metres (4.4 feet) away from the bicycle, whereas the average truck got 19 centimetres (7.5 inches) closer and the average bus 23 centimetres (9 inches) closer.” That’s especially discouraging, given how the relative masses of a cyclist and a bus affect the dynamics of a possible colission.

A more comprehensive examination of the results (PDF) is available online.

The situation demonstrates the kind of game theory situation so common in safety and security. If you fall by the grace of your own actions, you are better off wearing a helmet. If a car actually does hit you, having a helmet is probably also a good idea. The degree of trade-off between reducing the probability of occurrence and mitigating the probable consequences is rarely easy to set effectively.

The take home lesson: there is a bit more reason to be wary of helmets, but cross-dressing could save your life.

Author: Milan

In the spring of 2005, I graduated from the University of British Columbia with a degree in International Relations and a general focus in the area of environmental politics. In the fall of 2005, I began reading for an M.Phil in IR at Wadham College, Oxford. Outside school, I am very interested in photography, writing, and the outdoors. I am writing this blog to keep in touch with friends and family around the world, provide a more personal view of graduate student life in Oxford, and pass on some lessons I've learned here.

7 thoughts on “Helmets and driver psychology”

  1. Usually, if I were forced to wear a helmet I would choose to walk instead. Taking the wind in your hair away from cycling is like taking the sun away from a summer holiday – you’re left with, nothing.

  2. When I feel the wind in my hair while cycling, I immediately think: “Ack! I forgot my helmet!”

    I have probably spent less than thirty minutes in my life pedaling a bike without a helmet on, almost all of it in tiny segments a few seconds long.

  3. I tend to avoid helmets when cycling, except for a few scenarios. Generally my safety hinges on awareness and the assumption that no car driver sees me; I avoid things which may hit me – so having extra noise generated by wind in a helmet impacts the useful sounds I can pick up. That said, if I am in a city I will usually wear one, as I need to budget for more random manoevres by pedestrians, cars, other cyclists etc

  4. I don’t see how cross-dressing would save my life.
    Perhaps the smart conclusion is to wear a helmet and ride on bike routes and quiet (non bus and truck carrying) roads whenever possible.

  5. Sarah,

    I realized from the outset that that sentence wasn’t very inclusive, but it is a lot funnier than a more qualified version would be.

    The re-opening of Ottawa’s snow-clogged bike paths is hotly anticipated.

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