By Chris McCahill
Reducing excessive speeding is one of the most effective ways to improve road safety—especially where people are walking or biking. While lowering speed limits and adding traffic calming measures help, growing research highlights the value of self-explaining streets that give drivers constant cues to slow down.
For decades, road designers have aimed to simplify roads by clearing roadside obstacles and removing on-street parking, hoping to reduce crashes. But reform-minded engineers like Wes Marshall and Chuck Marohn have argued that these designs can backfire. When roads feel safer, drivers often compensate by speeding up and paying less attention.
In fact, several recent studies show that drivers behave more cautiously in environments they perceive as complex or risky. One study from Switzerland found that drivers associate more complicated roads with lower safe speeds. Streets with on-street parking, for example, were seen as the most complex and least safe, leading drivers to slow down.
Interestingly, streets with bike lanes were seen as simpler and safer. Drivers reported feeling comfortable going 30 mph or faster on these roads—the highest speeds of any road type in the study.
Fortunately, when participants were placed in a virtual reality driving simulator, their behavior told a different story. On simulated urban streets with posted speed limits around 19 miles per hour (30 km per hour), average speeds hovered around 21 miles per hour, plus or minus 5%. Some design elements had a larger impact than others: street trees caused the greatest speed reductions, while wide centerlines encouraged higher speeds.
Another study that spanned 15 cities in five states found similar results in the real world. Drivers tended to go slower in areas with more buildings and grass medians, while speeds increased in open spaces with clear views of the sky. The researchers explain:
These features [buildings] may serve as a visual cue for drivers to perceive a more urban or populated area, which tends to prompt them to drive at lower speeds. On the other hand, monotonous or featureless environments, such as long stretches of highway without much visual variety, can contribute to speeding.
Road design sends powerful signals. More complexity—whether through buildings, trees, or parked cars—can help keep speeds in check and streets safer for everyone.
Photo credit: Jonathan J. Castellon via Unsplash. License.