Although traffic circles and roundabouts use a circular design, they operate very differently. Traffic circles are very large and are designed for high-speed vehicle operation. Roundabouts are designed as small as possible, 16 to 180 feet wide, and operate at 15 mph to 25 mph.
The design of roundabouts forces drivers to slow as they approach them, then limits drivers' circulating and exit speed. It is difficult to pass through a well-designed roundabout above these design speeds.
In addition to slow vehicle speeds, modern roundabouts require drivers to slow and select gaps in the circulating traffic before entering the roundabout at low speed.