You know the experience. You’re in your car, just trundling along when, as you cross the junction… “WHOA! He just came out of nowhere! If I hadn’t braked, that would have been a collision. Why do they let these idiots on the road?”
The classic study is Swenson (1981), who surveyed students in Sweden and the United States, asking subjects to compare their driving safety and skill to the other people in the experiment. Stop and think how you might answer this yourself. As a road user (whether in a vehicle or on foot), do you put yourself in the top ten percent for safety? the bottom ten percent? the top thirty percent? right in the middle (so that half of other road users are more safe than you, and the other half less safe)?
It’s clear that some sort of bias is at work when, looking at the first line of Swenson’s results, you see 60% of the US students putting themselves in the safest 20%. For driving skill, almost all of the US sample (93%) and 69% of the Swedish sample put themselves in the top 50%. For safety, 88% of the US group and 77% of the Swedish sample put themselves in the top 50%. (Note that being “in the top 50%” is different from being “above average”). This is an example of what’s known as superiority bias, or Lake Wobegon effect.
Whereas Swenson asked about driving skill and driving safety, a follow-up study asked subjects to evaluate eight different dimensions of their driving (McCormick et al. (1986)). They had to say where they were on the dangerous-safe dimension, the considerate-inconsiderate dimension, and so on. Out of 178 subjects, only a tiny minority of responses were below average and for some of the measures, large majorities rated themselves as above average. Taking the eight dimensions together, just under 80% of the subjects put themselves above the average driver.
For me, the most powerful demonstration of this bias was an earlier study that inspired Swenson. Preston and Harris (1965) interviewed 50 drivers who were in hospital after road accidents; in 34 cases because of accidents they had caused. In written assessments of their own skill, they gave the same glowing self-evaluations as other drivers.
The practical consequences of superiority bias are that people take fewer precautions than necessary. According to Lewin (1982), only 10-15% of road accidents are purely down to mechanical or environmental factors. The remaining 85-90% are either human error (insufficient skill or attention) or a combination of factors. Another consequence is that people ignore road safety advice, because they think it is aimed at the worse-than-average drivers (you know, all those idiots on the roads) rather than them.
Another bias that might be at play is the illusion of control, where drivers have unrealistic expectations about their ability to avoid accidents. McKenna (1993) asked subjects how likely they were to be involved in different possible road accidents. Some were scenarios where the subject would have a lot of control, such as “an accident in which the vehicle you are in is driven into another vehicle”. Others were low-control, such as “an accident which is caused by another vehicle hitting you from behind”. The high-control scenarios were rated as much less likely, meaning that drivers think that their own control of the vehicle is unlikely (less likely than average) to result in an accident.
Let’s think again about that near-miss at an intersection. There probably won’t be much interaction between the two drivers other than honks and rude hand signs, but if we could listen in on the other car, the driver might well be saying, “Hey, look where you’re going! If I hadn’t swerved, that would have been a collision. Why do they let these idiots on the road?”
Lewin I. (1982) “Driver training: A perceptual-motor skill approach” Ergonomics 2.5, 917-924. doi:10.1080/00140138208925051
McCormick, Iain A., Frank H. Walkey and Dianne E. Green (1986) “Comparative perceptions of driver ability— A confirmation and expansion” Accident Analysis & Prevention. Volume 18, Issue 3, June 1986, Pages 205-208 doi:10.1016/0001-4575(86)90004-7
McKenna, F. P. (1993) “It won’t happen to me: Unrealisitic optimism or illusion of control?” British Journal of Psychology, 84, 39-50
Preston, Caroline E. and Stanley Harris (1965) “Psychology of drivers in traffic accidents” Journal of Applied Psychology
Volume 49, Issue 4, Pages 284-288 doi:10.1037/h0022453
Swenson, O. (1981) “Are we all less risky and more skillful than our fellow drivers?” Acta Psychologica, Volume 47, Issue 2, February 1981, Pages 143-148 doi:10.1016/0001-6918(81)90005-6