What is the difference between a "traffic circle" and a roundabout?

Roundabouts are different from traffic circles in that traffic circles can involve stop signs, stop signals, or no control at all; traffic circles can be very large, operate at higher speeds and confusing to navigate, often requiring motorists to move from one lane to another.

Some traffic circles still exist (Belleville Square); however, safety and operational problems caused many of them to fall out of favor in the 1950s and 1960s.

Roundabouts are not traffic circles.  Roundabouts follow a yield at entry rule, which requires approaching vehicles to wait for a gap in the circulating traffic before entering the roundabout.  Roundabouts involve low speeds for traffic entering and driving through the roundabout; they use deflection to slow entering traffic and enhance safety. Vehicles in the roundabout have the right of way.

Another distinguishing difference between traffic circles and roundabouts is that roundabouts have a smaller diameter than most traffic circles, resulting in safer conditions and lower speeds. Vehicles can enter modern roundabouts much easier than traffic circles due to flared approaches, entry angles, slower speeds on the circulating roadway and the fact that vehicles entering roundabouts always yield to circulating traffic.

Entering a roundabout is as easy as making a right hand turn onto a one-way street.