You may be surprised to learn that the Roundabout Capital of America is Carmel, Indiana. It is a small town just north of Indianapolis:
The mayor, Jim Brainard, built the first roundabout in Carmel in 1997 after seeing them in Britain. Instead of a four-way intersection with traffic lights, a circular bit of road appeared. It was so successful that today Carmel is the roundabout capital of America, and the mayor plans to rip out all but one of his remaining 30 traffic lights.
One of their main attractions, says Mayor Brainard, is safety. The Insurance Institute for Highway Safety, an independent research group, estimates that converting intersections with traffic lights to roundabouts reduces all crashes by 37% and crashes that involve an injury by 75%. At traffic lights the most common accidents are faster, right-angled collisions. These crashes are eliminated with roundabouts because vehicles travel more slowly and in the same direction. The most common accident is a sideswipe, generally no more than a cosmetic annoyance.
What locals like, though, is that it is on average far quicker to traverse a series of roundabouts than a similar number of stop lights. Indeed, one national study of ten intersections that could have been turned into roundabouts found that vehicle delays would have been reduced by 62-74% (nationally saving 325,000 hours of motorists’ time annually). Moreover, because fewer vehicles had to wait for traffic lights, 235,000 gallons of fuel could have been saved.
You can read more on the city’s webpage.