Traffic circles are raised islands, placed in intersections, around which traffic circulates.  Traffic circles are good for calming intersections, especially within neighborhoods, where large vehicle traffic is not a major concern, but speeds, volumes, and safety are problems.  Traffic circles have the advantage of calming two streets at once.  They may require the elimination of some on-street parking.  Entry may be stop controlled.  Average speed reductions of 4 MPH are typical as are collision reductions of 11%.  This device functions best at intersections that have four legs.  Some traffic circles provide an opportunity for landscaping, typically maintained by the neighborhood, which can soften the look and feel of the street.