Features of roundabouts include one way traffic flow, yield at entry and the curvature of the roundabout
One way traffic flow: Pavement markings, curves at entry points, and raised islands direct traffic into a one-way counter-clockwise flow around the central island.
Yield at entry: Traffic entering the circle yields to traffic already in the circle. This prevents the intersection from "locking up" which could happen if the traffic in the roundabout would have to stop for entering traffic.
Yield at entry: The radius of the roundabout and the angles of entry, created by the design of the medians and the center island, slow the speed of all vehicles to around 15-25 mph.