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Controlled-access highway

A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway,[a] motorway,[b] and expressway.[c] Other similar terms include throughway or thruway[d] and parkway. Some of these may be limited-access highways, although this term can also refer to a class of highways with somewhat less isolation from other traffic.

"Control of access", "Freeway", and "Motorway" redirect here. For the security concept, see Access management. For the 2012 Chinese film, see Motorway (film). For other uses, see Freeway (disambiguation) and Motorway (disambiguation).

In countries following the Vienna convention, the motorway qualification implies that walking and parking are forbidden.


A fully 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,[2] while increasing traffic capacity and speed.


Controlled-access highways evolved during the first half of the 20th century. Italy was the first country in the world to build controlled-access highways reserved for fast traffic and for motor vehicles only.[3][4] Italy opened its first autostrada in 1924, A8, connecting Milan to Varese. Germany began to build its first controlled-access autobahn without speed limits (30 kilometres [19 mi] on what is now A555, then referred to as a dual highway) in 1932 between Cologne and Bonn. It then rapidly constructed the first[5] nationwide system of such roads. The first North American freeways (known as parkways) opened in the New York City area in the 1920s. Britain, heavily influenced by the railways, did not build its first motorway, the Preston By-pass (M6), until 1958.


Most technologically advanced nations feature an extensive network of freeways or motorways to provide high-capacity urban travel, or high-speed rural travel, or both. Many have a national-level or even international-level (e.g. European E route) system of route numbering.

A typical design speed in the range of 100–130 km/h (62–81 mph)

Minimum values for horizontal curve radii around 750 to 900 m (2,460 to 2,950 ft).

Maximum longitudinal gradients typically not exceeding 4% to 5%.

Cross sections incorporating a minimum of two through-traffic lanes for each direction of travel, with a typical width of 3.50 to 3.75 m (11 ft 6 in to 12 ft 4 in) each, separated by a central median.

An obstacle-free zone varying from 4.5 to 10 m (15 to 33 ft), or alternatively installation of appropriate vehicle restraint systems.

Proper design of grade-separated interchanges to provide for the movement of traffic between two or more roadways on different levels.

More frequent (compared to other road types) construction of tunnels and overpasses, requiring complex equipment and methods of operation.

Installation of highly efficient road equipment and traffic control devices.

[32]

for single vehicle accidents, the 6-minute average speed on the fast lane; and the time headway (on every lane),

for multiple vehicle accidents, the occupancy, and the time headway (for the middle lane).

Metroad, used in Metropolitan Sydney and Brisbane before the implementation of Alpha Numeric Route markers

Metroad, used in Metropolitan Sydney and Brisbane before the implementation of Alpha Numeric Route markers

National Route marker, used in Sydney for the Western Freeway and the Princes Motorway (then F6 Freeway). Still in use in Western Australia.

National Route marker, used in Sydney for the Western Freeway and the Princes Motorway (then F6 Freeway). Still in use in Western Australia.

State Route marker, used for Motorways in Brisbane and Western Australia

State Route marker, used for Motorways in Brisbane and Western Australia

National Highway, used for the Pacific Motorway (then F3 Fwy) and Hume Freeway/Highway

National Highway, used for the Pacific Motorway (then F3 Fwy) and Hume Freeway/Highway

Alpha Numeric route marker. Replaced all previous route markers in Sydney and Victoria. Partially in Brisbane.

Alpha Numeric route marker. Replaced all previous route markers in Sydney and Victoria. Partially in Brisbane.

Autoroute Est-Ouest, near Ghomri, Relizane Province

Autoroute Est-Ouest, near Ghomri, Relizane Province

Autoroute A2 near Bouira

Autoroute A2 near Bouira

List of controlled-access highway systems

Media related to Controlled-access highways at Wikimedia Commons