LANSING, Mich. (Michigan News Source) – A report has been released by MDOT (Michigan Department of Transportation) called “Evaluating the Performance and Safety Effectiveness of Roundabouts – an Update.” The study was started in March of 2021 and in the 146 pages, it concludes that although crashes are more common at roundabouts, there are still benefits including the fact that they are less severe.
The two-year study cost the taxpayers $210,000 and was done to analyze the safety, operational and environmental effects on Michigan’s 180 roundabouts in comparison to traditional intersections.
The MDOT Research Administration put out a project information sheet along with the study and said, “Roundabouts have well-documented traffic and safety benefits compared to many types of traditional intersections. As design standards have evolved and the number of roundabouts has more than doubled in Michigan over the last decade, a new assessment of the safety and operational effects of existing roundabouts and their environmental and economic impacts gives the Michigan Department of Transportation (MDOT) valuable insight for designing and constructing future roundabouts across the state.”
The information sheet continues to say, “Since Michigan’s first modern roundabout was built in 1996, more than 180 have been installed statewide to replace intersections that previously had traffic signals or stop signs. In addition to their well-established safety benefits, roundabouts improve traffic flow and reduce traveler delays, fuel consumption and air pollution.”
In the report, MDOT points to a previous 2011 study that also demonstrated the safety benefits and cost-effectiveness of the then-58 roundabouts in Michigan and another study the same year that evaluated driver behavior and developed a public education campaign to encourage support and increase user confidence.
MDOT says, “Since then, roundabout designs and safety features have evolved, many more roundabouts have been built and MDOT and transportation agencies around the state are planning more.”
The results of the study include historical and field data collection, comparisons to traditional intersections and data analysis which revealed some important performance differences among roundabout designs and site characteristics. In their results, they concluded the following:
Safety impacts: Based on a review of the crash data for 142 roundabouts, the research showed that crashes occur more often at roundabouts than at traditional intersections. However, crashes at roundabouts are less likely to result in severe injuries or deaths.
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Operational and environmental impacts: Compared to traditional intersections, roundabouts were found to reduce traffic delays by more than 63 percent on average and estimated fuel savings were more than $69 per vehicle per year. Also, converting an existing intersection to a roundabout generally results in benefits six times greater than the costs of the conversion.
Driver behavior: A roundabout’s geometry, and other variables such as traffic volume and the presence of warning signs, influenced drivers’ speeds as they entered the roundabout. Drivers accepted smaller gaps at roundabouts with more than one lane, three-legged roundabouts and those located in rural areas. Roundabouts on interchanges, where speeds tend to be higher, had the lowest yielding rates toward pedestrians and other vehicles while roundabouts with pedestrian hybrid beacons produced higher yield rates than those without.
Lastly, to help MDOT transportation planners determine whether converting a traditional intersection to a roundabout would be beneficial, researchers recommended traffic modeling tools that can predict the number of crashes at an intersection based on its design and other characteristics.
MODOT will incorporate these findings into its Safe System Approach for eliminating fatalities and serious injuries for all road users, and may investigate additional opportunities and accommodations to make roundabouts safer for pedestrians and non-motorists.
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