You may not personally enjoy using roundabouts. They can be intimidating, especially the multi-lane ones. They’re unfamiliar to many, with traffic light controlled intersections being by far the norm. But once you see how drastically injury rates from crashes drop from implementing an unusual roundabout design nicknamed the “dogbone,” you might rethink your hesitation.
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The city of Carmel, Indiana, has become a living laboratory of sorts for roundabout design, with more than 100 in place—more, it’s claimed, than any other American city. Several of the new-style roundabouts, also known as double-teardrops, were installed in Carmel at several busy, higher-speed intersections. The Insurance Institute for Highway Safety compared the accident rate after installation with two years’ worth of data before construction. The result? A staggering 63 percent drop in total crashes of all types, and an 84 percent reduction in crashes resulting in injury.
The dogbone roundabouts are employed in places where a fast arterial or highway intersects a smaller street. It’s a bit like a cloverleaf interchange, but with the additional benefit of slowing and separating traffic converging at the center of the intersecting road. The diagram here explains the flow. The main benefits are reducing overall speed (but also keeping traffic flowing, compared to a red light holding up traffic) and physically separating traffic to prevent oncoming and right-angle collisions.
It’s not entirely sunshine and roses, as it takes a while for drivers to get used to roundabout flow patterns. With conventional multilane roundabouts, IIHS found, there was an increase in minor crashes that were chalked up to driver unfamiliarity. But as drivers get used to traffic flow, these minor crashes are expected to decline. Either way, the benefits of roundabouts—and particularly the novel dogbone roundabout—are adding up as more studies on American roundabouts are completed.
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