Many studies cite major Roundabout benefits including reduced delays and improved overall safety, particularly in reducing the severest of intersection crashes and the number of injuries and fatalities experienced.
Reasons for the reduced number and severity of accidents at modern Roundabout applications include:
o 75 percent fewer vehicle conflict points compared to a conventional intersection design
o physical guidance and separation of the various movements
o lower and consistent speeds traversing the roundabout
o pedestrians cross only one direction of travel at a time
In a survey of U.S. departments of transportation, the main reasons highway agencies considered and/or constructed Roundabout s i ncluded greater safety, shorter delays, lower costs and improved aesthetics /urban design. Reasons given for not building Roundabout s included uncertainty that drivers could adjust, and questions about operations and safety.
Appropriate locations for Roundabouts include locations where there is insufficient room for adequate queue storage, such as at interchanges or at entrances to bridges and tunnels. Other potential candidates include intersections with high accident rates, particularly accidents involving cross street through and/or left-turn movements. Poor candidates include intersections of roads with highly imbalanced approach volumes, which give a disproportionate advantage to the low-volume approaches.
Problems encountered at existing Roundabout locations that should be evaluated in new Roundabout design processes have included increased maintenance costs for the central island (additional or difficult snow removal, additional sign costs, and the need to do maintenance at night), lack of signalized pedestrian crossings, larger vehicles running over central islands, and how to locate driveways near Roundabout entrances.
Though a thorough investigation of design and construction costs has not been undertaken, a sampling of dual-lane Roundabouts on state highways has shown a cost range of $350,000 to $500,000 per installation (excluding right-of-way), varying with size, drainage and landscaping costs
