Multi Modal Benefits:

Compared to signalized intersections or freeway interchanges, roundabouts are multi-modal friendly. It is easier for pedestrians to cross a roundabout intersection as the crossing can be done in two stages with only one-way traffic in each stage and a safe haven in between. Roundabouts have "splitter islands" that provide this temporary refuge. In addition, traffic speed within the roundabout is slow even on otherwise high speed thoroughfares as traffic is calmed as it approaches, enters, navigates and exits the roundabout. Urban roundabout pedestrian accident rates are approximately half those at urban traffic signals. Because of the slower speeds in roundabouts, bicyclists can utilize the same travel lane as cars, thereby reducing the likelihood of collisions with automobiles.

Fiscal Benefits:

When planned as part of new road construction, roundabouts are less expensive to build than signalized intersections and have reduced annual maintenance and operational costs when compared to signalized intersections. Unlike traffic signals, roundabouts have no additional maintenance costs other than general road care. They require no electricity, no regular tune-ups, no annual replacements of parts, suffer no blackouts and cannot be blown away.

Aesthetic Benefits:

Although the primary function of roundabouts is intersection control, their secondary role as a traffic calming element is perfect for creating gateways to communities and main streets as they slow traffic and provide space for a grand entrance statement. Roundabouts are aesthetically pleasing and can become an urban focal point or civic feature. They can act as a town square with fountains, statues, landscaping or other features creating a focal point. Businesses located on or near newly installed roundabouts often report an increase in business perhaps due to the enhanced aesthetics provided by the roundabout and safety for pedestrians and drivers alike.

Air quality benefits:

When vehicles idle in a queue they emit approximately seven times as much carbon monoxide as vehicles traveling at 10 mph. When delays are low at roundabouts, the emissions from roundabouts are very small as traffic rarely stops, whereas traffic always stops at signals regardless of the amount of traffic. Studies in the U.K. indicate that if delays at a roundabout and a signal are similar, the emissions from the signalized intersection are always greater because the stop time at signals is longer than at roundabouts. Emissions from a stopped vehicle are approximately 4.5 times greater than a vehicle moving at 5 mph.

Wayne Elson, U.S. Environmental Protection Agency, compiled a summary of seven studies in regards to the findings for air quality components and vehicle emissions [see www.cccnh.org/cccwayneelson.htm]. In the studies that reported quantitative results, roundabouts reduced vehicle emissions for hydrocarbons in five studies averaging 33%, carbon monoxide in six studies averaging 36%, and nitric oxides in six studies averaging 21%. Five of the study results were based on emissions modeling. One study (Kvatch, 1998) used instrumented vehicles. In another study ambient air quality monitoring correlated well with emissions estimates (Mustafa, 1993). "No extensive examination of the air quality effects of a series of roundabouts was found in the literature. It is thought that the traffic calming effects may extend as far as 300 feet from the intersection and reduce emissions between roundabouts. The regional scale air quality benefits of roundabouts would depend on their percent contribution to regional mobile source emissions." Further, "roundabouts are one more option to be considered when attempting to decide which form of traffic control will best suit a specific situation. The air quality benefits indicated by these studies have implications for transportation planners and air quality planners in dealing with State Implementation Plans under the Clean Air Act, Transportation Control Measures, Transportation Conformity determinations and National Environmental Policy Act studies and alternative analyses."