Raised, elongated islands placed on the centerline of streets are commonly called medians.  Medians come in many sizes and can be designed to follow the curvature of a street.  Medians are often landscaped to provide a visual amenity.  Placed at the entrance to a neighborhood, medians can become "gateway islands."  Fitted with a gap to allow pedestrians to walk through at a crosswalk, they are often called "pedestrian refuges."  Medians can be used to narrow lanes, or to provide physical separation from traffic.  While they provide an average 7% decrease in travel speeds, their speed-reducing effect is somewhat limited where there is an absence of any vertical or horizontal deflection.  Medians can visually enhance a roadway when landscaped.  They may also reduce parking and driveway access, but can be a preferred traffic calming measure for emergency response.