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Education And Debate

For and againstDoes risk homoeostasis theory have implications for road safetyForAgainst

BMJ 2002; 324 doi: (Published 11 May 2002) Cite this as: BMJ 2002;324:1149

Does risk homoeostasis theory have implications for road safety

Risk homoeostasis (also called risk compensation) theory predicts that, as safety features are added to vehicles and roads, drivers tend to increase their exposure to collision risk because they feel better protected. Gerald Wilde provides evidence for it and suggests that it should be used to inform road safety strategies. Leon Robertson and Barry Pless, however, argue that the evidence is deeply flawed and that the theory is little better than an excuse for doing nothing


  1. Gerald J S Wilde (, professor emeritus of psychology
  1. Department of Psychology, Queen's University, Kingston, Ontario, Canada
  2. a 11 Dixon CT, Nogales, AZ 85621, USA,
  3. b Montreal Children's Hospital, C538 2300 Tupper, Montreal QC H3H 1P3, Canada

    Anyone wishing to reduce the risk of misfortune on the road to zero can do so by never using the roads, but that person would also miss all the benefits accruing from road travel and thus live a greatly diminished life. Suboptimal risk taking also occurs if a person underestimates or overestimates the danger of a given activity, because that person would either take too much risk or too little for greatest net benefit. A person learns to assess risk by perceiving the outcomes of decisions. Our intuitive assessment of risk is honed by our experience and that of others, sometimes communicated through the mass media. This feedback will thus confirm or correct a person's perception of the size of the four utility factors that determine the optimal (or target) level of risk (see box).

    Theory of risk homoeostasis

    While some actions entail more danger (probability×magnitude of loss) than others, there is no behaviour without some risk. The challenge, therefore, is to optimise rather than eliminate risk. This optimal, or target, level of risk is that which maximises the overall benefit (probability×amount). Four utility factors determine the target level of risk:

    • The expected benefits of risky (comparatively dangerous) behaviour options

    • The expected costs of comparatively cautious behaviour options

    • The expected benefits of comparatively cautious behaviour options

    • The expected costs of risky behaviour options.

    The first two factors increase …

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