Wednesday, 18 March 2009

Offsetting Behaviour

A nice example of offsetting behaviour, via Popular Mechanics. They even cite Peltzman!
Give people antilock brakes, airbags and other safety devices, and they “consume” the safety improvements by driving more aggressively. This phenomenon is called the Peltzman Effect, after economist Sam Peltzman, who first wrote about it in 1976. The decades-long effort to make highways straighter, wider and better-marked, with more guardrails and rumble strips, has eliminated one class of dangers only to foster another: the complacent driver with a cellphone in one hand and a cup of coffee in the other, steering the vehicle with a knee while occasionally glancing at what’s ahead.

Meanwhile, modifying roads and intersections so drivers are less comfortable—by making driving, in some ways, more dangerous—forces people to slow down and pay attention, producing a change in behavior that, paradoxically, results in more safety. This is also true for pedestrians, who Vanderbilt says are more cautious away from crosswalks than within them because they don’t know if cars will actually stop.

Solution? See my masthead...


  1. This addresses the problem of safety, but isn't there a safety-speed/efficiency tradeoff? Isn't it a highly productive use of one's time to [have a] "cellphone in one hand and a cup of coffee in the other, steering the vehicle with a knee while occasionally glancing at what’s ahead"?

    If I am looking for a total chance of dying of .001, isn't it better to fulfill it AND go fast/talk on the phone rather than fulfill it going slowly and being prevented from multitasking?

  2. Of course people get value from being able to pay less attention to their driving. I wouldn't begrudge them it at all. Rather, policymakers ought to give some thought to the offsetting effects when crafting policy. So, in making cars safer, they may simultaneously increase the number of accidents, decrease the car occupants' fatality rate, and increase the fatality rate for pedestrians.

    Drivers are always optimizing. It's the externalities that are the problem for me, especially when the externalities are exacerbated by government regulations inducing the externality.

  3. I couldn't agree more... I wonder how privately owned roadways/highways would try to solve this problem?

  4. Max Marty- they wouldn't care, they'd just sue you for any damage to their roadway.

  5. I/S: that isn't quite true. Imagine that you're the owner of a road and you want to maximize profits. People are willing to pay less to drive on your road if there's a high chance that a lunatic will kill them while they're driving on it. So, you'll want to have some minimal safety standards. You'll keep increasing the safety standards until the cost of imposing them doesn't bring in enough extra toll revenue to cover the costs.