AASHTO Journal - State DOTs Highlight How Roundabouts Improve Safety

Several state departments of transportation recently illustrated how the installation of roundabouts or traffic circles can help improve safety and efficiency at roadway intersections as part of National Roundabouts Week; an annual event spearheaded by the Federal Highway Administration.

[Above photo by Mississippi DOT]

Roundabouts and traffic circles move traffic in a counterclockwise direction around a center island, easing congestion. Its channelized, curved approaches force vehicles to slow down without requiring them to stop and, instead, yield to crossing pedestrians or bicyclists and traffic already in the circle.

Generally, traffic circles are large, with speeds rarely less than 30 mph, while roundabouts are smaller with speeds rarely rising above 25 mph.

To highlight the safety benefits of roundabouts, the Ohio Department of Transportation recently released an analysis of crash data from 76 intersections statewide that had been converted to roundabouts. That analysis indicated single lane roundabouts decreased injury crashes by 69 percent while multi-lane roundabouts resulted in a 25 percent decline.

“Safety is the driving force behind every decision we make, and the results are clear, roundabouts are very effective at reducing crashes and saving lives,” said Pamela Boratyn, director of the Ohio DOT, in a statement. “Our goal is to continue to support our local, county, and state partners by providing funding for roundabouts.”

She noted that, in July, Ohio Governor Mike DeWine (R) issued an additional $137 million for 55 traffic safety projects statewide – with 25 of those projects including the installing roundabouts.

[Editor’s note: This Ohio DOT video takes a closer look at a traffic circle in the Town of Somerset before and after its conversion to a roundabout – and how that change improved safety.]

The Pennsylvania Department of Transportation noted that since 2005, it has installed more than 104 roundabouts with more than 30 additional roundabouts in various stages of design and construction across the state.

“For us, it’s simple. Roundabouts remove cross-traffic turns and eliminate T-bone crashes, while improving traffic flow,” said PennDOT Secretary Mike Carroll in a statement. “Any design that dramatically reduces the most serious crashes we see on the road is worthy of consideration in our projects.”

PennDOT finalized a data review through 2024 using 20 years of crash data from roundabouts around the state, finding that crashes with injuries dropped by 51 percent while total crashes decreased by 7 percent due to their installation.

The agency noted that Pennsylvania’s data reflects national studies that found changing two-way sign-controlled intersections to a single-lane roundabout reduced injury crashes by more than 80 percent. Likewise, changing a signalized intersection to single-lane or multilane roundabout reduced crashes with injuries by up to 78 percent. PennDOT said.

In Texas some 661 roundabouts are currently in place, with more coming. The Texas Department of Transportation noted in a recent news release that more than 90 roundabout locations are now in stages of planning or early design, with 27 roundabouts already in detailed design in nine TxDOT districts statewide.

The agency seeks to build more roundabouts because not only are they more resilient during severe weather situations, but they can also be much safer compared to a typical traffic light intersection.

Data gathered by the Mississippi Department of Transportation helps back that contention up; indicating that the configuration of roundabouts results in a significant 78 percent to 82 percent decline in fatal and serious injuries at formerly signalized and two-way stop-controlled intersections.

“Conflict points are minimized in roundabouts, which ultimately reduces crashes that result in injuries and fatalities. Along with the glaring safety benefits, roundabouts keep people moving and reduce idle wait times,” said Brad White, Mississippi DOT executive director, in a statement. “We aim to highlight these ongoing efforts to improve road safety and traffic management across the state.”