Roundabouts on North Dakota’s highway system reduced the number of traffic crashes and fatalities and serious injuries in crashes, according to a study by the state Department of Transportation.

Across 12 locations, the average crash rate declined by 33 percent, total crashes per year dropped by 36 percent, and fatal and serious injury crashes per year decreased by 59 percent.

The study analyzed five years of crash data at 12 locations where roundabouts were installed between 2012 and 2021. One location was excluded from the average due to lack of volume data.

After roundabouts were installed, angle crashes were more of a merging crash between a vehicle entering the roundabout and a vehicle already circulating within the roundabout, according to the study. Roundabouts virtually eliminate the number of head-on and high-speed right-angle, or T-bone, collisions.

The proportion of rear-end crashes decreased by 22 percent while single-vehicle crashes increased by 55 percent. Almost half of single-vehicle crashes involved overturning or shifting load when circulating the roundabout and going straight into the roundabout’s center of the island.

North Dakota built its first highway roundabout in 2012 and today there are 14 on the state transportation system. Another 13 are planned to be installed in the next few years.

Read more about roundabouts in this story from InTransition.

The full study and other resources are available here.