What is a Modern Roundabout?

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.