An intersection with 3 or more approach legs, generally circular in shape where continuous flow of traffic is allowed through the use of the yield and merge maneuvers.
The following is taken from “Pedestrian Crosswalk Signal at Roundabouts: Where are they Applicable?”
by Bill Baranowski, P.E., Roundabouts, USA
A typical modern roundabout is an unsignalized intersection with a circular central island and a circulatory roadway around the island. Vehicles entering the roundabout yield to vehicles already on the circulatory roadway. Roundabouts have raised splinter islands at each approach that separate the entry and exit lanes of a street. These splinter islands are designed to deflect traffic and thus reduce speed. Splinter islands also provide a pedestrian refuge between the inbound and outbound lanes.
Engineers use a variety of design techniques, mostly geometric, to slow vehicles as they approach, circulate, and exit a roundabout. Design practices from Europe and Australia continue to influence U.S. engineers as they refine approaches for application in urban, suburban, and rural areas. Studies conducted in western Europe €“ where roundabouts are common €“ and in the U.S. have found that crashes at roundabouts are les severe than vehicular crashes at traditional intersections. The reduction in serious vehicular crashes is the most compelling reason cited by transportation engineers for the installation of roundabouts. Roundabouts increase vehicular safety for two main reasons: (1) they reduce or eliminate the risk arising at signalized intersections when motorists misjudge gaps in oncoming traffic and turn across the path of an approaching vehicle; and (2) they eliminate the crashes that occur when vehicles are hit broadside by vehicles on the opposing street that have run a red light or a stop/yield sign.