Three features separate the modern roundabout from other forms of circular intersections.
(i) Diameter less than 100m, or 330′. A modern roundabout has a typical ICD (Inscribed Circle Diameter) of 90-150′ for a single lane, or 160-240′ for a two lane.
(ii) Yield on entry – vehicles within the roundabout always have the right-of-way. Older traffic circles often forced traffic within the circle to yield to entering vehicles.
(iii) Entry path deflection. Vehicles entering a roundabout must be guided by curbs or other channelization along a path which slows their speed before entering the circle.
Frequently Asked Questions
Will a roundabout work at a location with heavy pedestrian traffic?
Yes, in fact many roundabouts have been installed adjacent to schools and universities.
Will a roundabout work at a location with a railroad crossing?
Several are in operation near light and heavy rail alike.