A controlled-access highway is a highway designed exclusively for high-speed vehicular traffic, with all traffic flow and ingress/egress regulated. They are known by various terms worldwide, including Autobahn, autostrada, autopista, autoroute, freeway, motorway, otoyol, snelweg, thruway, and sometimes less precise terms such as expressway, highway, Interstate, or 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.
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. Entrance and exit 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 central reservation containing a traffic barrier or just a strip of grass.