Roundabouts : an informational guide

The guidance supplied in this document is based on established international and U.S. practices and is supplemented by recent research. The guide is comprehensive in recognition of the diverse needs of transportation professionals and the public for introductory material through design detail, as well as the wide range of potential applications of roundabout intersections. The following topics are addressed: definition of a roundabout and what distinguishes roundabouts from traffic circles; public acceptance and legal issues associated with roundabouts; consideration of all user modes, including heavy vehicles, buses, transit, bicycles, and pedestrians; a methodology for identifying appropriate sites for roundabouts and the range of conditions for which roundabouts offer optimal performance; methodologies for estimating roundabout capacity, delays, and queues with reference to the Highway Capacity Manual; design principles and guidance on safety and geometric design, with reference to applicable national standards such as the AASHTO Policy on Geometric Design of Highways and Streets; guidelines for control features such as signing and pavement markings, with reference to the Manual on Uniform Traffic Control Devices; illumination; and landscaping.