Making roads safer makes them more dangerous . . .

Glenn Harlan Reynolds writes in the latest issue of Popular Mechanics:

Reading Tom Vanderbilt’s latest book, Traffic: Why We Drive the Way We Do (and What It Says About Us), I was struck by a recurring theme: Making things safer may actually make them more dangerous. . . .

There is a fair amount of scientific evidence that backs up Vanderbilt’s insights. 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.

Another ramification here is that as motor vehicle occupants feel safer, they take more risks. The result for those inside the automobile is the risk stays about the same. But for those outside the car--including pedestrians, bicyclists, and motorcyclists--the risk of fast and distracted driving by other increases greatly and there is no off-setting safety improvement.