RoundaboutsBack to News

As discussed in the recent New York Times and New Urban News articles; many communities in the USA are beginning to learn and appreciate a design feature which has been in common use in Europe for decades, the use of roundabouts.

Roundabouts reduce initial infrastructure costs and environmental burdens while combining smooth operation for all users with lower maintenance costs, making roundabouts attractive to Cities, environmentalists, economists and engineers alike. Improved landscaping areas and iconic features also help differentiate a community and provide a sense of place.

Responding to negative experiences in roundabout design during the 1990’s, and a lack of national standards for planning, performance, and design of roundabouts, the Federal Highway Administration (FHWA) provided a comprehensive design guide in June 2000. The benchmark FHWA Guide is supplemented by ongoing lessons learned as more on the ground examples can be reviewed. Currently between 150 and 250 roundabouts are built in the United States each year.

The most significant advantage of incorporating roundabouts in design is the safety benefit at intersections. Since over 9,000 fatalities occur at intersection-related crashes annually, FHWA recommends the use of roundabouts, where appropriate, with designs accommodating all users (drivers, pedestrians, and bicyclists) of all abilities. Roundabouts reduce the likelihood of side-impact crashes, a severe collision type, by forcing motorists to enter and exit the roundabout through right-turns. A 2000 study by the Insurance Institute for Highway Safety (IIHS) which evaluated 24 intersections across the United States and revealed the following:
• 39% decrease in accidents;
• 76% decrease in injury crashes;
• 90% reduction in crashes involving fatal or incapacitating injuries.

The recognition of safety at roundabouts has led some State DOT’s to enforce a “Roundabout First” policy to evaluate feasibility of using roundabouts in preference to traffic signals. Despite studies showing improved traffic operations, engineers within the industry are still polarized on the subject of roundabouts. Some City Traffic Engineers flatly rule out the use of roundabouts. Changing attitudes are expected as positive roundabout examples are implemented and adopted by engineers and motorists alike

A 2003 IIHS study compared roundabouts versus traffic signals in several locations. They concluded that roundabouts in those locations provided the following traffic operations benefits:
• 74% decrease in vehicle delay;
• 300,000 hours of motorist delay savings;
• 200,000 gallons of fuel savings; and
• 30% reduction in Greenhouse Gas emissions.

Often cited as a traffic calming measure, roundabouts provide continuous flow through intersections, and reduced roadway speeds. Lifecycle costs show lower costs of roundabouts versus traffic signals, as equipment and energy costs are reduced. Where roadways “flare” or widen at intersections, roadways approaching roundabouts narrow, minimizing pedestrian crossing distances and infrastructure construction and maintenance costs. The reduction in roadway widths has the potential to reduce a 4-lane neighborhood collector to a 2-lane collector, substantially reducing land dedicated to infrastructure and environmental impacts. Reduced pavement area directly correlates with infrastructure costs, and reduced stormwater runoff. Speeds through modern roundabouts are better managed through design characteristics grounded in physics rather than signs or police enforcement.

On the softer side, roundabouts are often used within new communities to provide an iconic gateway or serve in placemaking to differentiate a community. The roundabout center island and the “median islands” that guide approaching cars provides increased landscaping areas, and often fits well with a signature community tree while still serving engineering benefits of sight distance and visibility.