Risk control is not risk adjustment: the zero-risk theory of driver behaviour and its implications

Abstract

The zero-risk theory, originally presented by Näätänen and Summala (1974, 1976 a), posits that due to human perceptual, cognitive, and motivational processes, drivers adapt to risks on the road, whilst being motivated towards faster speeds and objectively more risky behaviour. In decision-theoretic terms, both the subjective probability distribution of the outcomes of drivers' behaviour and their speed-utility function are severely distorted. Drivers are not, however, adjusting risk. With experience, driving simply becomes a habitual, largely automatized activity in which risk control is based on maintaining safety margins. Because of this adaptation to risk and the motives involved, drivers are not able to take traffic risks into account to a degree that would be rational from their own point of view and that of society. The main implication of the theory is that we have to prevent this tendency for drivers to be motivated towards higher speeds and thus to adapt to greater risk in the traffic system. The primary means of doing so are restrictive. Speed limits are therefore a necessary condition of effective traffic-safety work.