Roundabout design and functionality increase capacity and safety, and reduce delay:

• Traffic is always moving, as compared to signalized intersections where there is considerable dead time and start-up time.
• Design slows vehicles down thereby allowing tightly spaced circulating traffic, and safe and efficient weaving in multi-lane roundabouts.
• Design acts to slow traffic rather than enticing them to speed up to make a green light.
• Slow speeds and fewer possible conflicts and tangential movements create a safer intersection.
• Roundabouts are secondarily an effective traffic calming device since they force vehicles to reduce their speed upon approaching the intersection, thereby creating safer intersections for all users, including bicyclists and pedestrians, thereby enhancing the inter-modality capacity of a roadway.
• Design allows for larger left turn radii than signalized intersections and "truck aprons" so that trucks, emergency vehicles, and other large vehicles can comfortably navigate the roundabout and make left turns.
• Roundabout design offers superior performance at intersections with more than four legs, such as the village of Chatham on Route 41.
• Because traffic from each approach can simultaneously enter a roundabout, the capacity is typically higher than at stop-controlled or signalized intersections. A one-lane roundabout typically has a capacity of 2,500 to 2,800 vehicles per hour.

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Approximately 75 - 80% of daily traffic is outside of the A.M. and P.M. peak periods. Roundabouts which operate well in peak periods, have virtually no queues or delays outside of the peak periods. When the average peak hour delays are similar at roundabouts and traffic signals, drivers prefer roundabouts, as they do not "get caught" by a red light. A regular small delay is preferable to the gamble of no delay versus a long red delay. Queues at traffic signals are stationary, but at roundabouts vehicles continuously move. This is much preferred by drivers, as they perceive continuous movement and they never experience the complete halt of a red light.

Roundabouts are suitable for both low and very high traffic volumes. Capacities of up to 8,000 vehicles per hour have been achieved in the U.K. in multi-laned roundabouts, according to the Barry Crown Report. Roundabouts are easy to modify if circumstances change as very small changes in geometry give large increases in capacity. Single lane roundabouts can easily be converted without great expense to two or three lane roundabouts if capacity warrants.

Several studies are proving superior operational efficiencies for roundabouts in comparison to traditional signalized intersections. A Kansas State University study for one roundabout showed statistically significant reductions in five Measures of Efficiency used: 14.1% drop in queue length, a 34.4% decrease in maximum approach delay, 33.3% decrease in proportion stopped, 46.7% drop in maximum proportion stopped, and 13.3% drop in degree of saturation. The IIHS study done in Kansas, Maryland and Nevada, comparing before and after delays, proved that installation of roundabouts reduced the amount of traffic having to stop at intersections, resulting in an overall 20% reduction in delay. [Russell, Luttrel, Rys, 2002].

New design standards were formally adopted in the United Kingdom in 1984, formally establishing the "modern roundabout" with three principal features: yield to traffic in the circle, deflection at entry, and low design speed controlled by amount of deflection. Any circular intersection designed and built prior to the mid-1980s is not a modern roundabout. (Russell, Luttrell, Rys; Roundabout Studies in Kansas)