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.
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."