Unsignalized Intersections: Roundabouts

Europe has made extensive use of roundabouts for many decades, and traffic circles, often around significant monuments, have been around for centuries. While some traffic circles and roundabouts have always existed in the U.S., interest in their ability to reduce delays (compared to signalized intersections) and create safer and more efficient flow began to increase in the 1980s and 1990s. A formal methodology for analysis of roundabouts first appeared in the 1997 update to the 1985 HCM [1]. It was somewhat expanded (editorially) for 2000, and significantly expanded in 2010, with minor changes in 2016.