Wednesday, November 12, 2008

Traffic safety: speeding

Traffic safety is a big problem for adolescents. Injury is the leading cause of adolescent death, and traffic accidents where an adolescent is the driver is probably a large portion of that. Most studies of the question that I've heard of have concluded that everyone would be much better off if driving licenses weren't given until 18, and some places have instituted graduated licenses for 16 and 17 year olds.

With that background, here is a study of adults about the perceptions of whether speeding is safe: the vast majority of adults perceive speeding is safe, and safety is proportion to their perception of their likelihood get caught. I've observed this myself: everyone knows the slogan "speed kills", many know that kinetic energy is proportional to the square of velocity (i.e., so each incremental speed increase raises the risk even more). Some may even know that the majority of children survive being hit by a car going 25 mph, but the majority die being hit by a car going 40 mph. And everyone speeds. It may be an issue of overconfidence in driving abilities since nearly all drivers believe they are above average drivers; availability, since all drivers have either gotten a ticket or know someone who has, but few know those who have been in accidents; and all kinds of other psychological fallacies.

With this attitude prevalent among adults, it is almost unimaginable that adolescents would get a safe message about driving. It may even be futile to try to change adolescents' attitudes and behavior in the face of such widespread adult opposition. It seems that any campaign to prevent adolescent traffic injury would have to start with adults' attitudes, but how? How much increased enforcement of speed limits would it take? Is that even possible in crowded urban highways where the average speed is 10+ mph faster than the posted speed limit?

Here's the paper's abstract:

In recent decades, it has become more common for speed limits to be set for political reasons rather than for safety reasons. As a consequence, the motoring public seems to have increasingly begun questioning the rationality of speed limits. This is evident in observed speed data that show that the majority of drivers routinely exceed posted speed limits. A key motivating factor in drivers’ tendency to exceed the speed limit is that they believe that the excess speed does not threaten safety. This paper, specifically studies this matter by using a survey that asked drivers how fast above the speed limit they feel they can drive before safety is threatened. A probabilistic model is estimated using data gathered from 988 drivers in Indiana. Estimation findings show that drivers’ perception of the speed above the speed limit at which they will receive a speeding ticket is a critical determinant of what they believe is a safe speed – suggesting that enforcement plays an important role in safety perceptions. Other variables found to be significant factors in determining the speed above the speed limit at which safety is first threatened include age, gender, being previously stopped for speeding, and drivers’ ethnicity.

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