A controlled-access highway is a type of highway which has been designed for high-speed vehicular traffic, with all traffic flow and ingress/egress regulated. Common English terms are freeway (in Australia, South Africa and parts of the United States and Canada ), motorway (in the United Kingdom, Pakistan, Ireland, New Zealand and parts of Australia ), expressway (in some parts of Canada, parts of the United States, and many Asian countries ), and autoroute (in Québec, Canada ). Other similar terms include Interstate and parkway. Some of these may be limited-access highways, although this term can also refer to a class of highway with somewhat less isolation from other traffic.
In countries following the Vienna convention, the motorway qualification implies they are forbidden from walking or parking, and reserved for the use of motorized vehicles only.
A controlled-access highway provides an unhindered flow of traffic, with no traffic signals, intersections or property access. They are free of any at-grade crossings with other roads, railways, or pedestrian paths, which are instead carried by overpasses and underpasses. Entrances and exits to the highway are provided at interchanges by slip roads (ramps), which allow for speed changes between the highway and arterials and collector roads. On the controlled-access highway, opposing directions of travel are generally separated by a median strip or central reservation containing a traffic barrier or grass. Elimination of conflicts with other directions of traffic dramatically improves safety and capacity.
