A roundabout is one of several types of circular road junctions or intersections at which traffic is slowed down and enters a one-way stream around a central island. These junctions are sometimes called Modern Roundabouts, in order to emphasize the distinction from older circular junction types which had different design characteristics and rules of operation. In the United States, those older designs are commonly referred to as “rotaries” or “traffic circles”.
Statistically, roundabouts are much safer for drivers and pedestrians than both traffic circles and traditional intersections. Roundabouts have shown to reduce fatal crashes by 90 percent, injury crashes by 75 percent, and pedestrian crashes by 30 to 40 percent.
Because low speeds are required for traffic entering roundabouts they are not designed for high-speed motorways (expressways). When such roads are redesigned to take advantage of roundabout principles, steps are taken to reduce the speed of traffic, such as adding additional curves on the approaches.</p>
Large old traffic circles are not modern roundabouts
The Benbrook Traffic Circle in west Fort Worth is an example of an old-style, large traffic circle. Modern traffic circles are more compact and function differently.
Roundabouts are not the same as traffic circles or rotaries. Traffic circles or rotaries have high-speed entries, weaving in the circle, low capacity, and many high-speed crashes. Sometimes motorists in the circle must yield to those entering as is the case for the Weatherford Circle shown in the figure. They are large and challenging to drive — at times a “free for all”.
The photo to the right shows a roundabout being constructed within the central island of a large rotary in New York State. The roundabout is much smaller, yet will be safer and higher-capacity.
Roundabouts are the opposite of traffic circles
Modern roundabouts require motorists to yield on entry. There is no weaving. Speeds are low, capacity is high, and crashes are few and minor. They are comfortable to drive, and, if designed well, almost everyone likes them after a trial period.
Yield at entry
Entering traffic yields to circulating traffic. Circulating traffic always keeps moving.
Roundabouts are also compact compared to their older traffic circle cousins. Modern roundabouts operate with slower speeds and do not trade off safety for traffic capacity while balancing travel provisions for all users.