Here in Madison, the traffic engineering dept. has instructions for using traffic circles. According to the city:
Traffic circles slow down traffic by forcing drivers to slow to a speed that allows them to comfortably maneuver around them.
- Is it legal to go left around a traffic circle?
Please see the guide for safe driving around a traffic circle.
- What is the impact of traffic circles on vehicle speeds?
Traffic circles have been reported to reduce midblock speed by about 10%.
- What are the other benefits of traffic circles?
Reduction in intersection collisions on average by 70% and overall collisions by 28%.
Traffic circles are different from roundabouts. 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.
See the video below of a bicyclist hit while cycling through a roundabout.