Editor’s note: This vendible was written in response to our coverage of National Roundabouts Week 2022. Read the other wares in the series here. 

As roundabouts subtract traffic deaths for drivers, some designs of the controversial traffic treatment may unquestionably increase collisions for people on bikes while scaring others off riding entirely, a series of studies suggests — and its raising thorny questions well-nigh who might get hurt withal the road to Vision Zero.

As part of an ongoing study of the safety impacts of roundabouts, Utah State University-based researchers Patrick Singleton and Nirajan Poudel surveyed 49 studies from roughly a dozen countries and terminated that, on the aggregate, roundabouts may unquestionably increase crashes between bicyclists and drivers — and in some cases, they increase serious injuries and deaths of people on two wheels, too.

The operative word in that sentence, of course, is “may” — and Singleton is shielding to point out that not all roundabouts are created equal. Researchers in Belgium, for instance, recorded a staggering 93 percent increase in injury crashes at the intersections that weren’t outfitted with twin protected velocipede lanes; meanwhile, Danish researchers studied roundabouts that did have separated lanes, and logged an almost-as-staggering 84 percent reduction in crashes. United States academics, by contrast, often struggled to yank any definitive conclusions, considering there were so few roundabouts, crashes, or plane simply bicyclists in U.S. communities.

But Singleton still says that roundabout safety deserves increasingly scrutiny, particularly in light of the many studies in their sample that examined how unsafe cyclists feel when riding in many of them. Though very crash data is often treated as the gold standard of safety metrics, other research shows that low levels of “perceived safety” can dissuade people not just from riding at a unrepealable intersection, but from riding entirely. 

“We took a very wholesale and loose definition of ‘safety’ in this review,” Singleton added. “The end goal of Vision Zero, of course, is that we want to reduce injuries and deaths on our roadways. But the process of getting there matters, so we wanted to assess perceptions of repletion and safety as well.”

In subsequent studies, Singleton and Poudel looked increasingly tightly into cyclists’ perceptions of roundabout safety, interviewing 600 U.S. riders well-nigh what specific designs were most well-flavored to them and analyzing commonalities between their preferences.

The most popular options, they found, had “one (rather than two) lanes, lower traffic volumes, and increasingly robust bicycle facilities — expressly separated bicycle lanes (a ‘protected roundabout’).”

Which is, to put it bluntly, pretty much nothing like what the stereotype U.S. roundabout looks like at all.

“Current diamond guidance in the U.S. basically says to either let cyclists take the lane like a driver, or requite them a ramp to ride up on the sidewalk,” Singleton added. “But our study suggests neither of those are desirable to bicyclists.”

Part of the reason, Singleton says, is what psychologists undeniability “inattentional blindness,” when drivers physically see someone unexpected — like a cyclist riding right withal next to them, or plane on a sidewalk— but their brains goof to truly register that the unexpected person is there, considering the environment doesn’t unmistakably signal that they belong.

“If I’m a driver, I expect to mostly see things in the driving lane that are well-nigh the same size and speed as a car,” Singleton adds. “Needless to say, that’s not what a cyclist looks like at all. … As engineers and planners, we need to understand that ‘looking’ and ‘seeing’ are variegated things, and we need to diamond intersections to highlight vulnerable road users in many variegated ways.”

Singleton — who is moreover a starchy engineer himself — says that in wing to protected lanes, lots of signs and pavement markings, as well as good setbacks can moreover help ensure motorists don’t strike bikers plane when they’re looking right at them.

But he moreover recognizes that unconfined roundabouts that incorporate those recommendations can be significantly increasingly expensive and complicated to install — and that plane some imperfect ones can significantly cut crash severity when compared to signalized intersections, if not unchangingly crash volumes themselves. How transportation leaders negotiate those tradeoffs in the context of a Vision Zero plan, though, is a complicated political question that Singleton says it’s up to others to answer.

“I’m lucky that I’m the researcher and not the policymaker,” he laughs. “Hopefully I can provide information, and they can wrestle with those kinds of dilemmas. In the U.S., we’ve had quite a bit of wits to suggest that roundabouts are safer in a lot of situations. My weightier recommendation now is, let’s make them plane largest for bicyclists.”