Full signalization of the circulatory roadway

Full signalization that includes control of circulating traffic at junctions with major entrances is possible at large-diameter multilane traffic circles or rotaries that have adequate storage space on the circulatory roadway. The double-lane roundabout dimensions resulting from the design criteria recommended in this guide may preclude such possibilities. As stated previously, full signalization should in any case only be considered as a retrofit alternative resulting from unanticipated traffic demands. Other feasible alternatives should also be considered, such as flaring critical approaches, along with the associated widening of the circulatory roadway; converting a large-diameter rotary to a more compact modern roundabout form; or converting to a conventional signalized intersection. This guide recommends that signalizing roundabouts to improve capacity be considered only when it is the most cost-effective solution.

Traffic signals at fully signalized rotaries should be timed carefully to prevent queuing on the circulatory roadway by ensuring adequate traffic progression of circulating traffic and especially critical movements. Introducing continuous or part-time signals on the circulatory roadway requires careful design of geometry, signs, lane markings, and signal timing settings, and literature on this specific topic should be consulted (1, 2).