A shared-use path or mixed-use path is a form of infrastructure that supports multiple recreation and transportation opportunities, such as walking, bicycling, inline skating and people in wheelchairs. Motorcycles are normally prohibited. A shared-use path typically has a surface that is asphalt, concrete, or firmly packed crushed aggregate. In the U.S., the 1999 AASHTO Guide for the Development of Bicycle Facilities defines a shared-use path as being physically separated from motor vehicular traffic with an open space or barrier. Shared-use paths differ from exclusive bikeways in that shared-use paths are designed to include pedestrians even if the primary anticipated users are cyclists. Some shared paths have been built as rail trails.