A roundabout is an intersection built with a circular island around which traffic rotates in one direction. Many older roundabouts (which were also called traffic circles or rotaries) were built primarily as a location for a fountain or statue, with little regard to traffic principles. As a result, there has been considerable variation in design features and traffic regulation, causing confusion and accidents.
During the late Twentieth Century, traffic engineering organizations developed roundabout design standards and management practices to maximize traffic efficiency and safety. These are called "Modern Roundabouts".
They have the following features.
Yield at Entry. Traffic entering the roundabout yields the right-of-
way to the circulating traffic. This prevents traffic from locking-up and allows free flow movement.
Deflection. The entry lane is designed with a small deflector island to reinforce the yielding process and slow traffic.
Limited size. Modern roundabouts usually have just one, and never more than two, rotating lanes.
In addition, there are mini-roundabouts, which are small traffic circles located within local intersections. They still require yield-at-entry but do not have a deflector island.
Research has shown that roundabouts can improve reduce vehicle stops and delays, reduce traffic speeds, and increase safety compared with other intersection designs. They are also used to provide a gateway or aesthetic feature. As a result, roundabouts are once again being promoted by traffic engineers and planners, and are an important Traffic Calming tool. To maximize safety and establish consistency it is very important that all roundabouts be designed (and existing ones redesigned) to reflect Modern Roundabout principles.
While small, slow speed, single lane traffic circles are easily negotiated by cyclists and people with visual disabilities, larger roundabouts with 20 km/h or higher traffic speeds can be difficult to negotiate.
Reprinted from TDM Encyclopedia - Victoria Transport Policy Institute
