MnDOT study: Roundabouts significantly reduce fatal accidents

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State and local traffic engineers have long believed that roundabouts can improve safety at busy intersections — and now they have more data to back up those claims.

A new Minnesota Department of Transportation study of 144 roundabouts throughout Minnesota found an 86 percent reduction in the fatal crash rate at intersections after roundabouts were built. At the same time, MnDOT found that minor “property damage” accidents became more frequent.

Derek Leuer, a MnDOT traffic study engineer, said the biggest factor in reducing serious and fatal injuries is the elimination of “T-bone” accidents in which the front of one car crashes into the side of another.

“Within the roundabout you can’t get a T-bone crash anymore and the geometrics of the road are such that it compels you to slow down as you approach,” Leuer said. “And once you get to the intersection everyone is moving in the same direction.”

The study, released last week, examined crash data before and after a roundabout was built. MnDOT says it’s the biggest roundabout study conducted to date in Minnesota.

In all, it looked at 104 roundabouts with only one lane and 40 with more than one. Of that total, 120 were in urban areas and 24 in rural locations. Not included wee low-traffic sites and roundabouts that serve only residential areas, small business parks or private settings.

Crashes that resulted in “property damage” but didn’t cause injuries were up by 75 percent in “unbalanced” roundabouts, whose lanes vary in number at different spots in the circle.

And property damage crashes soared by more than 200 percent in “full dual” roundabouts, which have two circulating lanes at each approach.

But there were far fewer crashes resulting in bodily harm. Serious-injury crashes were down 83 percent, according to the 35-page study. For single-lane roundabouts, injury crashes plunged 61 percent and right-angle crashes were down 69 percent.

The cost of building a roundabout is about the same as a typical signalized intersection, according to MnDOT.

But they’re still a hard sell to the public in some cases. Critics say they are confusing for drivers, unsafe for pedestrians and cumbersome for large trucks to navigate.

Brooklyn Park is the birthplace of roundabouts in Minnesota. Even so, the Brooklyn Park City Council rejected plans in 2011 for the construction of a roundabout at the intersection of Brookdale Drive and Xerxes Avenue, despite the federal government’s having plans to provide 90 percent of the needed money. The decision was made in part in response to concerns about safety and businesses cut off from traffic.

Still, the construction of roundabout has accelerate in Minnesota in the past two decades.

Minnesota’s first roundabout was built 22 years ago, at Setzler and Neddersen parkways in Brooklyn Park, according to the study. A second roundabout was built about 10 years later at 108th Avenue and Regent Avenue in Brooklyn Park, City Engineer Jesse Struve said.

Struve said the city would consider future roundabout proposals on a “case-by-case basis.”

“It’s certainly something we would evaluate,” Struve said.

In 2005, Finance & Commerce reported there were about 15 “true roundabouts” in Minnesota that year. Now the state is home to nearly 200 roundabouts, MnDOT says.

For Leuer, the big lesson from the MnDOT study is that roundabouts can go a long way toward eliminating serious crashes.

“Bumpers and door panels can be replaced. People can’t,” Leuer said. “What we really want to reduce are those fatal and serious-injury crashes, and (roundabouts) have been effective in doing that.”