Roundabouts

The first Minnesota modern roundabout was constructed in 1995. Since then, roundabouts have been built across the state by the Minnesota Department of Transportation, counties, and cities. There is no definitive count across Minnesota, but it is likely nearing 200 roundabouts across the state on all roads. They have become an increasingly popular intersection type by traffic engineers, communities, and transportation officials. The purpose of this report is to examine the safety performance of roundabouts by comparing the before construction crash rates and the after construction crash rates and traffic volume data. Overall, roundabouts are performing well when looking at the crash reduction record. Roundabouts in Minnesota have had over an 80% reduction in fatal and serious injury crashes. At the time of this report, there still has not been a multi-vehicle fatality in a roundabout in Minnesota

Roundabouts have been effective at increasing safety and efficiency of vehicle traffic. Traditional roundabout design typically requires a larger “footprint” than a traditional four-way intersection. Over the past few years, more and more agencies are implementing “mini roundabouts,” a type of roundabout characterized by a small diameter that can include fully traversable islands (central island and splitter islands). Currently, there are over 40 mini-roundabouts in Minnesota. The focus of this document was to help Minnesota agencies learn a little more about mini-roundabouts.

This research summary accompanies Report 2024-14, "Evaluation of Traffic Safety for Heavy Commercial Vehicles at Roundabouts in Minnesota," published in May 2024.

Modern roundabouts have been shown to be one of the safest methods of control for at-grade intersections. An evaluation of traffic safety at roundabouts published by MnDOT in 2017 shows substantial decreases in fatal and serious injury crashes at intersections after installation of a roundabout. Despite these benefits, concerns have been raised from citizens, commercial motor vehicle (CMV) drivers, and other stakeholders about the propensity for roundabouts to cause more rollover crashes for larger vehicles. The purpose of this evaluation is to further evaluate the safety of heavy commercial vehicles at roundabouts, investigate whether rollover crashes are more likely to occur at roundabouts, and break down the most common characteristics for CMV crashes at roundabouts in Minnesota. This report includes the results of an analysis comparing roundabouts to signalized intersections. The results of this evaluation indicate that roundabouts continue to be one of the safest forms of intersection control for heavy commercial vehicles, especially when compared to traffic signal control. Although roundabouts have experienced a greater number of rollover crashes compared to intersections with traffic signal control, their installation results in a decrease in high-severity crashes.

By the end of 2022, nearly 450 roundabouts were installed on Minnesota roadways. An evaluation of traffic safety at roundabouts published by MnDOT in 2017 showed substantial decreases in fatal and serious injury crashes for all users at intersections after installation of a roundabout. The safety effects of roundabouts are largely due to geometric design practices that reduce the speed of motorized vehicles as they approach and travel through the intersection. The purpose of this evaluation is to determine if the safety effects seen in the 2017 evaluation still apply to roundabouts with higher levels of use by pedestrians and bicyclists. This evaluation conducts a before-after analysis of 95 roundabouts in Minnesota and an analysis comparing roundabouts to untreated intersections. With the installation of a roundabout, this study finds that the before-after analysis results in a 40% decrease in all severity injury crashes for all roadway users, a 70% decrease in fatal and serious injury crashes for bikes and pedestrians, and a 15% decrease in total pedestrian bike and pedestrian crashes. The results of the comparison analyses suggest roundabouts have better safety performance than through-stop and traffic signal-controlled intersections and similar safety performance to locations with all-way stop control. The results of this evaluation thus indicate that roundabouts can be an effective safety treatment for pedestrian and bicycle crashes.

Includes photos of the construction of the Highway 43 roundabout at Winona in June 2022.

This Technical Summary pertains to the LRRB-produced Report 2017-30, “Evaluation of Safety and Mobility of Two-Lane Roundabouts,” published July 2017.

This Technical Summary pertains to the LRRB-produced Report 2017-14, “Strategies for Effective Roundabout Approach Speed Reduction,” published May 2017.