Controlled-access highway

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 the US), motorway (in the UK & Ireland) and expressway (in Canada and many Asian countries). Terms in other languages sometimes seen in English include Spanish: autopista or autovía (depending on whether it has toll or not), French: autoroute, German: Autobahn, or Italian: autostrada. Other similar terms include Interstate and parkway. They may also be called limited-access highways, although this term can also refer to a class of highway with somewhat less isolation from other traffic. Conversely, some of the United States use "controlled access" to describe a non-limited-access road, entrances to which are controlled by the state.

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 across the highway. Entrances and exits to the highway are provided at interchanges by slip roads (ramps), which allow for speed changes between the highway and arterial roads 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 the sources of potential conflicts with other directions of travelers dramatically improves safety, and capacity.