From Damn Interesting’s “The Balance of Risk“:
What’s happening is a process known as risk compensation. It’s a tendency in humans to increase risky behavior proportionately as safeguards are introduced, and it’s very common. So common, in fact, as to render predictions of how well any given piece of safety equipment will work almost useless.
… Why would we do such a strange thing? Dr. Gerald Wilde of Queens University in Ontario proposes a hypothesis he calls risk homeostasis. In a nutshell it proposes that human beings have a target level of risk with which they are most comfortable. When a given activity exceeds their comfort level, people will modify their behavior to reduce their risk until they are comfortable with their level of danger. So far, that’s not exactly a controversial observation. But risk homeostasis proposes another half to that continuum – according to Dr. Wilde, if a given person’s level of risk drops too far below their comfort level, they will again modify their behavior. This time though, they will increase their level of risk until they are once again in their target zone.
… Fortunately for us, risk homeostasis does not seem to apply in all cases. Safety innovations that are invisible tend not to provoke changes in behavior – for example changing windshields to safety glass does not alter most peoples’ driving behavior. The difference in the windshield is effectively invisible to the driver, and so doesn’t affect the driving.
… An additional complication for the already beleaguered safety engineers is that risk homeostasis is dependent not upon actual danger, but rather the perception of risk. Much of the gender and age differences in risk-taking behavior appear to stem less from differing desires for risk, and more from the individual’s different evaluation of risk. Young people, and particularly young men, tend to evaluate their level of risk as much lower than older people would, even in identical situations. This implies that promoting safer behavior depends more upon altering the perceptions of the target population, rather than improving the safety of the environment – a much trickier proposition.