Designing Streets with the Human Mind in Mind

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Failing to Account for Driver Psychology

Traffic engineering practices also don’t do a good enough job accounting for the psychology of drivers. We’ve written about this a lot over the years, including as it relates to perceived risk.

In one article, Chuck explained that every driver has a risk threshold. When the perceived risk of a particular street or road is below that threshold, drivers have a tendency to fill that “risk gap” with other activities: from changing the radio station and putting on makeup, to texting or speeding. I used to live in Nebraska, and I-80 between Lincoln and Omaha is flat and mostly straight. I knew people who used to read books as they drove that stretch of interstate; I did crossword puzzles and went too fast.

Traffic engineers want to make roads wider, straighter, and flatter—so-called “forgiving design”—but there is an unintended consequence: reducing the possibility of randomness widens the risk gap, which makes drivers more comfortable filling that gap with other risky activities.

Back in 2018, a fascinating study done in London found that removing safety railings at pedestrian crossings led to a significant reduction in deaths and injuries. And not only were people on foot less likely to be killed or seriously injured at these crossings, all road users, including people in cars, were safer. The likely explanation, according to the report’s authors? A shift in driver’s attitudes.

Sam Wright, the engineer tasked with removing the railings, told Auto Express:

Railings can sometimes give drivers “tunnel vision” and a feeling that pedestrians are safely tucked behind them.

Without the railings people tend to cross in more locations on an “ad hoc” basis. Rather than this being more dangerous, the feeling that pedestrians could step out from anywhere appears to make drivers slow down and pay more care and attention.

In addition the railings caused some pedestrians to become trapped in the road, taking longer to reach the safety of the footway. Removing them means they now actually spend less time in the road. As a result, junctions and crossings are safer without railings.

We need to design our streets and roads to be safe not for the predictable abstractions of our best-laid plans, but for the complex, unpredictable, flesh-and-blood people who actually use them. We need to #SlowTheCars. Doing that, as Chuck Marohn wrote in 2014 (a few months before Destiny Gonzalez was killed crossing State Street), means “not simply more efficient engineering but actually pondering driver psychology and asking difficult questions about how people respond to our designs. We don’t want people to perceive the road as safe; we want it to actually be safe.”

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