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IIHS Reports Roundabouts Reduce Crashes in Indiana City

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Aerial photo of a roundabout with one car driving around it
Photo: Pexels

Double-teardrop roundabouts in Carmel, Indiana, have not only helped the city earn the nickname “Roundabout City,” but have also significantly contributed to traffic safety. According to a report by the Insurance Institute for Highway Safety, the unique roundabouts have reduced injury crashes by 84 percent. It also revealed that all crashes have been decreased by approximately two-thirds. The roundabouts are located along Keystone Parkway.

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“Our results show that Carmel’s double-teardrop roundabouts are remarkably effective in preventing the most severe crashes,” says IIHS Vice President of Research Jessica Cicchino. “The main reason is that their design allows them to be installed at the most dangerous intersections.”

More than 100 roundabouts are located in Carmel. No other city in the United States can match that number. In addition to reducing crashes, roundabouts also reduce emissions and keep traffic moving despite the city’s population increase, according to Carmel Mayor James Brainard. In the early 1990s, the population of Carmel was tallied at approximately 25,000. Today, the number is close to 100,000 people.

IIHS study methodology

To compile the data on how roundabouts affect traffic safety, IIHS researchers “examined crash data from 64 roundabouts over the two years before and after their construction.”

The roundabouts, which were constructed between 2005 and 2017, varied and included 21 single-lane, 10 double-teardrop, and 33 multilane designs. Each design contributed to varying degrees of crash reductions.

“Single-lane roundabouts reduced total crashes and property-damage-only crashes by 51 percent and 50 percent, respectively, while multilane roundabouts were associated with increases in total crashes and property-damage crashes. Injury crashes dropped 50 percent at single-lane roundabouts and 15 percent at multilane roundabouts, though these estimates were not statistically significant,” according to the IIHS.

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The double-teardrop roundabout design, however, showed the highest impact on traffic safety. Crashes that involved injuries were reduced by 84 percent. A drop of 63 percent was noted for total crashes.