New study shows roundabouts are reducing crashes and improving traffic flow in Minnesota

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According to a new study released by the Minnesota Department of Transportation (MnDOT) the state’s nearly 200 roundabouts are reducing serious injuries and saving lives.

Minnesota built its first roundabout in 1995 in Brooklyn Park. Since then, MnDOT, counties and cities have built roundabouts across the state. There is no definitive count for Minnesota, but it is likely to be nearing 200 roundabouts across the state on all roads. They have become an increasingly popular intersection type by traffic engineers, communities and transportation officials. Roundabout types deployed in the state include single lanes, dual lanes, and unbalanced lanes, in settings such as rural, urban, suburban, interchange ramp terminals and higher and lower volume locations.

The new MnDOT’s roundabout study is the largest conducted in the state to date. Data from 144 individual sites were collected, including detailed information, by county and city, on each roundabout showing before and after installation crash rates and traffic volume. Sites with low traffic volumes and those that only service residential areas, small business parks or private settings were not studied.

The study examined the safety performance of roundabouts by comparing the before- and after-construction crash rates, and overall roundabouts are performing well. The study shows that there has not yet been a multi-vehicle fatality on a roundabout in Minnesota. There was an 86% reduction in the fatal crash rate at intersections where roundabouts were installed, and an 83% reduction in the serious injury crash rate.

The report also showed the following data at intersections with single-lane roundabouts (SLRs), the most common type of roundabout in the state:

• 69% reduction in right-angle crash rates;

• 83% reduction in the left-turn crash rates;

• 61% reduction in the injury crash rates;

• For all roundabout types, there was a 42% reduction in the injury crash rates.

Design features of roundabouts that help reduce serious crashes and fatalities include yield control of entering traffic, and channelized approaches and other geometric elements that control travel speeds, facilitate efficient exchange of traffic flows and minimize the number and severity of vehicle conflicts and crashes.

“Overall, roundabouts in Minnesota are performing well,” said Derek Leuer, MnDOT traffic safety engineer and author of the report. “In most cases, modern roundabouts compare favorably in safety and operational performance to conventional intersections with stop control or signalized operation. Roundabouts also have comparable initial construction costs and lower life-cycle costs than a traffic signal with similar traffic capacity.”

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Tom has edited Traffic Technology International magazine and the Traffic Technology Today website since he joined the company in May 2014. Prior to this he worked on some of the UK's leading consumer magazine titles including Men's Health and Glamour, beginning his career in journalism in 1997 after graduating with a law degree from the London School of Economics (LSE).

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