Designing Streets with the Human Mind in Mind

Image via Unsplash.

One reason traffic engineers end up harming the communities they are called to serve is that, when designing roads and streets, engineers don’t take into account the humanness of the people actually using those roads and streets.

Failing to Account for “Pedestrian” Psychology

For example, engineering practices are built on the assumption that people make the kind of predictable choices that turn them into abstractions known as “pedestrians.” But that’s often not the case, and assuming it is can bear tragic results.

Consider State Street in Springfield, Massachusetts. In December 2014, seven-year-old Destiny Gonzalez was struck and killed by a car as she was crossing the four-lane street in front of the library with her mother and cousin. Strong Towns president Chuck Marohn described the tragedy this way in a recent podcast: 

The desire path is the perhaps the single most elegant example of the kind of bottom-up feedback our cities should listen to when we're thinking about what to build next. Right now, your neighbors are literally voting with their feet. Listen to them. https://t.co/dnPhaOvml0

— Strong Towns (@StrongTowns) August 26, 2019

“If you take the standard engineering analysis, what happened is that a mom with these two young children failed to walk basically a football field in the rain, down to a light, late at night, wait for their turn to cross, then cross, and then walk a football field back up, in the rain, in a cold December night, to get to their parked vehicle. Instead, they chose a shorter route, a more logical route, and wound up with one of them dead as a result. The traditional engineering analysis of this is that the mom made a mistake, the mom should have followed the rules as a ‘pedestrian’ and done what our theoretical mapping on the street said a ‘pedestrian’ should do in this instance.”

The reality, Chuck continued, is that Destiny and her family weren’t “pedestrians.” They were humans. “And a big part of making things safe for people is engineers recognizing that humans are complex, they do weird things, and they do strange things, and they do things that are not always predictable. And that’s okay. But it should change our [street] design from being…as if we’re dealing with automatrons, to being more respectful of the fact that humans are messy.”

Strong Towns has compiled Google Street View images going back to 2007 that show people waiting for cars so they can cross State Street, as well as desire lines made by people who are taking the shortest path between the library and their vehicles. Accounting for the complexity and unpredictability of humans, and even just observing how the built environment is already being used, should compel engineers to design streets that are safer and more hospitable for people.

State Street, August 2007. (Image via Google Maps.)

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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