Does High-Tech Highway Design Make us Less Safe?

• auto safety
• safety
• security
• airbags
• helmets
• transportation
• traffic

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. I wonder if it’s a lesson that also applies off the road.

Vanderbilt describes driving along a narrow, twisting road in Spain, where he navigated hairpin turns with few guardrails or warning signs over steep drop-offs. The result: “I drove as if my life depended on it.” But when he reached a four-lane highway with gentle curves, good visibility and little traffic, “I just about fell asleep and ran off the road ... Lulled by safety, I’d acted more dangerously.”

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. 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.

Likewise, traffic circles and squares, which demand a driver’s full attention, turn out to be both safer and better at handling large volumes of traffic than traditional four-way intersections with traffic lights. In the former, people focus on what’s going on; in the latter, they relax and expect the traffic signals to do all the work. Drivers in traffic circles also communicate more with hand signals and eye contact. As Vanderbilt notes, when a traditional four-way intersection with lights was turned into a traffic square, “The responsibility for getting through the intersection was now up to the users, and they responded by communicating among themselves. The result was that the system was safer, even though the majority of users, polled in local surveys, felt that the system was more dangerous!”

Vanderbilt also says that change causes people to pay more attention, and hence drive more safely. In 1967, when Sweden switched from driving on the left to driving on the right, many people predicted that accidents would increase. But accident rates dropped noticeably, and took a year to return to the pre-changeover level. The change, and the fear of accidents it produced, caused people to drive more carefully. The lesson here is that familiarity breeds slackness, and regular challenges encourage mindfulness and attention. Instead of designing roads and devices to accommodate people who are dozing through life, we might produce better performance by designing things with an eye toward engaging attention.

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