MODERN ROUNDABOUT PRACTICE IN THE UNITED STATES

This synthesis presents information on current practices with respect to the planning, design, and operation of modern roundabouts in the United States. It will be of interest to state and local highway design engineers, traffic engineers, maintenance engineers, as well as officials concerned with roadway safety. It will also be useful to design and traffic engineering consultants who may be assisting communities with the implementation of roundabouts. The concept of the modern roundabout to move traffic more efficiently through unsignalized intersections has evolved from conventional traffic circles. This report of the Transportation Research Board presents a discussion of modern roundabout applications in the United States, based on a survey of state and local transportation agencies who provided information on 38 individual roundabouts. Case examples of three roundabouts, each representing a different type of roundabout, are described in detail. The synthesis presents information on the design guidelines used in the United States as well as those of other countries. Other major areas of interest with regard to roundabouts include safety issues; traffic capacities and delays; issues related to pedestrians, bicyclists, and the visually impaired; costs; and location criteria to be considered for roundabouts.