Mandatory wearing of seat belts reduces the likelihood of death or injury in case an accident happens, but does not reduce the death rate per capita.
In road sections where the accident rate per km driven is low, drivers move faster. Numerous other findings can be explained by risk homeostasis theory. Consequently, road users opted for less cautious behaviour alternatives and the fatal injury rate rose again. The level of perceived risk dropped and less often exceeded the target level of risk. After some time (f), however, people discovered-through the mass media as well as their own experiences-that the roads were not as dangerous as they had thought they were. As a result, the fatal injury rate dropped (box e). Road users adjusted their behaviour by choosing much more prudent behaviour alternatives (box d). Perceived risk (box b) was suddenly significantly higher than the target level of risk (box a). In terms of fig 1, what happened was a sudden surge in box b as a result of the changeover coming into effect. About a year and a half later, the accident rate returned to the trend before the changeover. This was followed by a marked reduction in the traffic fatality rate. In the fall of 1967 Sweden changed over from left hand to right hand traffic. There will be fluctuations in the room temperature, but averaged over time, the temperature will remain stable, unless the thermostat is set to a new target (set point) level. The phenomenon is similar to a thermostat: this instrument controls the actions of the heating/cooling unit which controls the temperature and this in turn controls the actions of the thermostat. This homeostatic mechanism is depicted in fig 1 and constitutes a case of circular causality: a change in the degree of caution displayed in behaviour brings about a change in the injury rate, while a change the injury rate also leads to a change in behaviour. This rate, in turn, has an effect on the level of risk that people perceive and thus upon their subsequent decisions, and so forth. Each action carries a certain level of injury likelihood such that the sum total of all actions taken by people over one year explains the accident rate for that year. 3 Risk homeostasis theory posits that people at any moment of time compare the amount of risk they perceive with their target level of risk and will adjust their behaviour in an attempt to eliminate any discrepancies between the two. The level of risk at which the net benefit is expected to maximize is called the target level of risk in recognition of the realization that people do not try to minimize risk (which would be zero at zero mobility), but instead attempt to optimize it. The expected costs of safe behaviour alternatives (examples: using an uncomfortable seat belt, being called a coward by one's peers, time loss). The expected benefits of safe behaviour alternatives (examples: insurance discounts for accident-free periods, enhancement of reputation of responsibility). The expected costs of risky behaviour alternatives (examples: speeding tickets, car repairs, insurance surcharges). The expected benefits of risky behaviour alternatives (examples: gaining time by speeding, fighting boredom, increasing mobility). In general, the amount of risk that people are willing (in fact, prefer) to take can be said to depend on four utility factors and will be greater to the extent that factors 1 and 4 are higher, and factors 2 and 3 are lower:
Both theory and data indicate that safety and lifestyle dependent health is unlikely to improve unless the amount of risk people are willing to take is reduced.īesides macroeconomic influences, there are other factors that influence the level of accepted risk these are of a cultural, social, or psychological kind. While these two policies seem logically contradictory, neither is likely to reduce the injury rate, because people adapt their behaviour to changes in environmental conditions. Here, people are threatened into adopting a safe behaviour a moment of inattention or carelessness may have a dire outcome. The second policy seeks to improve safety by making the consequences of imprudent behaviour more severe and includes things such as speed bumps, narrow street passages, and fines for violations. This policy offers forgiveness for a moment of inattention or carelessness. It may take the form of seat belt installation and wearing, airbags, crashworthy vehicle design, or forgiving roads (collapsible lamp posts and barriers). The first seeks to improve safety by alleviating the consequences of risky behaviour. There is an odd coexistence between two conflicting safety policies that may well be pursued by the same accident prevention agency.