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Roundabout intersection

A roundabout, rotary, or gyratory circus is a type of road junction (or traffic calming device) at which traffic streams circularly around a central island after first yielding to the circulating traffic. Roundabouts are also sometimes referred to as traffic circles, though technically a distinction between the two was made in the mid-1960s:

{| border=2 cellpadding=4 ! roundabout !! traffic circle |----- | Entering vehicles yield | Stop sign, stop signal, or giving priority to entering vehicles |----- | Vehicles in the roundabout have priority over the entering vehicle | Allow weaving areas to resolve conflicted movement |----- | Use deflection to maintain low speed operation | Some large circles provide straight path for higher speed |----- | No parking is allowed | Some large circles permit parking within the circle |----- | Pedestrians prohibited from the central island | Some large circles allow pedestrians on central island |----- | All vehicles circulate around the central island | Mini-traffic circles with left-turning vehicles passing to the left of the central island. |----- |colspan=2|(Source for table: Oregon Department of Transportation [1]) |}

British engineers reengineered the traffic circle in the mid-1960s to overcome its limitations of capacity and for safety issues. Unlike traffic circles, roundabouts operate with yield control to give priority to circulating traffic and eliminate much of the driver confusion associated with traffic circles and driver wait associated with signalized intersections. Roughly the same size as signalized intersections with the same capacity, roundabouts also are significantly smaller in diameter than traffic circles, separate incoming and outgoing traffic with pedestrian islands and therefore encourage slower and safer speeds (see traffic calming).

A diagram of movement within a roundabout in a country where traffic drives on the left

Roundabouts are safer than both traffic circles and traditional intersections -- having 40% fewer vehicle collisions, 80% fewer injuries and 90% fewer serious injuries and deaths (compared with a sampling of roundabouts in the United States with the intersections they replaced). Roundabouts also significantly reduce potential points of conflict between pedestrians and motorized traffic and are therefore considered to be safer for them. Roundabouts, especially large fast moving ones, are however unpopular with, and can be dangerous for cyclists.

In addition to improved vehicle and pedestrian safety, and in spite of lower speeds, roundabouts dramatically outperform traffic circles in terms of vehicle throughput and, because circular traffic is always moving, in roundabouts, they outperform signalized traffic signals as well.

However, due to the fact that vehicle traffic must yield instead of stop, there are some safety concerns for bicyclists who ride on pedestrian walkways and especially for persons with visual impairments. Safety concerns for the second group of people is especially important in countries that have legislation protecting the rights of people with disabilities.

A town in Wiltshire, England famous for its roundabouts is Swindon. It has a 'Magic Roundabout' which is made up of one large center roundabout and five smaller (mini) roundabouts around the center. Traffic is able to circulate in both directions around the main central rouindabout, with the normal rule applying at each mini-roundabout within. An even larger "magic" roundabout with six intersections exists in Hemel Hempstead, Hertfordshire.

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