Wisconsin’s Evaluation of Roundabout Safety

MSA Professional Services project manager discusses roundabouts


Morgan Fuerstenberg graphic

Amanda DeAmico, a project manager in the roundabout design group at the Madison-based engineering firm MSA Professional Services, visited campus on Oct. 4 to discuss the history of roundabout designs, implementations, research and development in Wisconsin.

DeAmico’s visit is the second installment in the five-part UW-Platteville Engineering Seminar Series for Fall 2022.

Associate Professor Danny Xiao introduced DeAmico as a “2009 proud Pioneer … (and) has had the privilege of collaborating with some of the nation’s leading roundabout designers, and has worked on hundreds of roundabout projects across the U.S.”

During her time at UW-Platteville, DeAmico worked two summers at a small engineering firm in Madison and “at that time, (roundabouts) weren’t as common,” said DeAmico.

The small engineering firm, MSA, grew into its role “to look at roundabouts, and we worked on roundabout projects across the country” explained DeAmico. Xiao added that DeAmico “has more than 14 years of experience focusing on solving intersection capacity and safety with modern roundabouts.”

Xiao explained that the ESS included this seminar about roundabouts because the Civil and Environmental Engineering program has a group of students working on intersection safety design and concerns. Xiao said, “The goal (of the ESS) is to expose students to a broader perspective and demonstrate how engineering contributes to our community.”

At the beginning of the seminar, DeAmico shared some background information about MSA and said, “We’re a full service-engineering firm (with) Civil and Environmental engineers.” DeAmico explained that “roadway projects involve a lot of other disciplines as well, so there’s a lot of collaboration with our store-water engineers, our environmental engineers (and) our electrical engineers.”

The presentation covered intersection safety, and defined the modern roundabout. It explained safety models that are applied to Intersection Control Evaluation and network screening to review roundabouts that are already in operation.

In Wisconsin, as of May 2021, there were 440 roundabouts installed. The first roundabout in Wisconsin was installed in 1999. A simplified version of the locations of Wisconsin’s roundabouts is public information, mapped out and available to view through the Wisconsin Department of Transportation at wisdot.maps.arcgis.com.

From a national focus on intersection safety, the Federal Highways Administration “identified four different areas that encompassed almost 90% of the traffic fatalities across the U.S., and those focused areas are roadway departure crashes, intersection-only crashes, pedestrian crashes and bicycle crashes,” DeAmico elaborated.

Roundabouts help target the safety issues with intersection crashes and pedestrian and bicycle crashes.

From data collected between 2016 and 2020, nearly 50% of fatal or injury crashes occur at intersections. In 2017, AAA reported that “939 people were killed nationally in red light running.”

“Being able to improve our intersections is a great way to reduce those fatal crashes,” she noted.

Roundabouts do exactly that. The geometry of roundabouts significantly decreases fatal crashes, as the angles of possible collision are less severe than traditional intersection with perpendicular traffic patterns. Additionally, there are 32 conflict points, or locations where traffic movements cross, in a traditional intersection. In contrast, roundabouts have eight points.

Roundabouts also simplify the scanning process for drivers. Drivers are prompted to look only to the left rather than also across and to the right. To reduce possible distraction, landscaping or mounds are sometimes installed in the center of the roundabout to block the sight of the cars entering across the roundabout. “All you need to do at a roundabout is look to your left,” advised DeAmico.

Locations across the U.S. that have replaced stop signs and traffic signals with roundabouts have had a 90% decrease in fatal crashes and a 76% decrease in accidents that lead to injury. Overall, there has been a 39% decrease in accidents at these locations with roundabout replacements.

Next, DeAmico explained the differences between a traffic circle and roundabout. 

Usually, traffic circles have large diameters, and they may be yield, stop or signal controlled. Traffic circles were built between the 1910s and 1920s and use the “first-in’’ rule, which leads drivers to race to the intersection rather than slow down at it like a roundabout. Due to the fast pace, the “yield to the right” law was introduced, which is still actively used today at intersections as well.

Another type of round intersection, called the rotary, was introduced in the U.S. in the 1930s. Rotaries are even larger than traffic circles in diameter. Rotaries allow drivers to merge while maintaining their entry speed. In rotaries with two lanes, inside lane drivers may find it difficult to exit. The high-speed traffic and confinement of the rotary led to over half of the rotaries in the U.S. being removed and replaced with modern roundabouts in the 1990s.

DeAmico then explained that modern roundabouts are “a compact circular intersection in which traffic flows counterclockwise around a center island” and in which “entering traffic yields.” They are “designed to slow the speed of vehicles,” she said. For this reason, roundabouts are suitable for accommodating high or low traffic, “especially intersections that have fluctuating flows, so say next to a school,” DeAmico added.

The yield sign was introduced in 1950 in Tulsa, Oklahoma by Police Officer Clinton E. Riggs, who was tired of writing tickets to drivers who were not quite stopping at intersections.

According to Northwestern Magazine, “Riggs placed the first yield sign at the most dangerous intersection in the city. Within a year, the number of accidents fell to zero, and yield signs soon appeared at intersections across the country … Clinton Riggs was a student at the Northwestern Traffic Institute in 1939 when he created the sign as a class assignment.”

The installation of yield signs became a standard method of traffic control. The U.K. then also installed yield signs at their roundabouts, “and they saw increased capacity, reduced delays for drivers” and reduced injuries. She concluded that “the invention of the yield sign led the way to modern roundabouts.”

DeAmico concluded the seminar by explaining safety models, Crash Modification Factors and Safety Performance Functions.

“(CMFs) estimate the change in crashes associated with applying a safety treatment or countermeasure,” she explained. CMFs are calculated by collecting data of the crash frequency at an intersection after a countermeasure is applied and dividing this amount by the crash frequency before the countermeasure was applied.

Recently, a more sophisticated model was developed: the SPF. This is “an equation that helps you predict the average number of crashes per year at an intersection based on your site’s characteristics.” SPFs work for roadway segments, intersections and, recently added to that list, roundabouts.

This new model factors in the average annual daily traffic entering a specific intersection as well as the site characteristics, such as the number of lanes, traffic control methods and median presence. SPFs help predict the number of fatal crashes, injury crashes and property-damage-only crashes using these variables.

In 2018, the WISDOT hired MSA, as well as Persaud & Lyon, to study 88 sites with roundabouts, which helped the WISDOT develop local SPFs. Property-damage-only crashes made up 84% of the crashes that occurred at the studied intersections. “Only 16% of the crashes were fatal or injury crashes,” said DeAmico. The study showed that roundabouts improved the safety of the intersections, thus providing more evidence in favor of the safety of the roundabout compared to its early round-intersection predecessors and the traditional intersection.

After the seminar on roundabouts and their impact on transportation, Xiao said, “As proved by theoretical analysis and field data, roundabouts can significantly reduce the severity of traffic accidents at intersections, meanwhile increasing the capacity and level of service.”