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Controlled-access highway

Highway designed for high-speed, regulated traffic flow

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Aerial photo of the US 131 / M-6 /68th Street interchange in Wyoming, Michigan looking north.
Michigan Department of Transportation · Public domain

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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, 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 connect cities with controlled-access highways reserved for fast traffic and for motor vehicles only. Italy opened its first autostrada in 1924, A8, connecting Milan to Varese. Germany since 1907 planned and in 1913 had started to built the AVUS in Berlin, but this 'Automobile traffic and training road' was a closed circuit with two long straights where vehicles could reach their top speed twice before returning to the entrance. Opened in 1921 and mainly used for testing and racing for two decades, the AVUS was connected in 1940 to the nationwide network of Reichsautobahn roads that was proposed in the 1920s by various initiatives, delayed by the Great Depression and built in the 1930s with tax money. In 1932, the first controlled-access autobahn without speed limits was completed between the Western German cities of Cologne and Bonn. The 30 kilometres [19 mi] on what is now A555 was then referred to as a dual highway. With plans having been made earlier, Germany rapidly constructed the first 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.

Definition standards

There are several international standards that give some definitions of words such as motorways, but there is no formal definition of the English language words such as freeway, motorway, and expressway, or of the equivalent words in other languages such as autoroute, Autobahn, autostrada, autocesta, autoput, that are accepted worldwide—in most cases these words are defined by local statute or design standards or regional international treaties. Descriptions that are widely used include:

Vienna Convention on Road Signs and Signals
"Motorway" means a road specially designed and built for motor traffic that does not serve properties bordering on it, and that:
  1. Is provided, except at special points or temporarily, with separate carriageways for the two directions of traffic, separated from each other either by a dividing strip not intended for traffic or, exceptionally, by other means;
  2. Does not cross at level with any road, railway or tramway track, or footpath; and,
  3. Is specially sign-posted as a motorway;

One green or blue symbol (like or ) appears at motorway entry in countries that follow the Vienna Convention. Exits are marked with another symbol: or .

The definitions of "motorway" from the OECD and PIARC are almost identical.

British Standards
Motorway: Limited-access dual carriageway road, not crossed on the same level by other traffic lanes, for the exclusive use of certain classes of motor vehicle.
ITE (including CITE)
Freeway: A divided major roadway with full control of access and with no crossings at grade. This definition applies to toll as well as toll-free roads.
Freeway A: This designates roadways with greater visual complexity and high traffic volumes. Usually this type of freeway will be found in metropolitan areas in or near the central core and will operate through much of the early evening hours of darkness at or near design capacity.
Freeway B: This designates all other divided roadways with full control of access where lighting is needed.

In the European Union, for statistical and safety purposes, some distinction might be made between motorway and expressway. For instance a principal arterial might be considered as:

Roads serving long distance and mainly interurban movements. Includes motorways (urban or rural) and expressways (road which does not serve properties bordering on it and which is provided with separate carriageways for the two directions of traffic). Principal arterials may cross through urban areas, serving suburban movements. The traffic is characterized by high speeds and full or partial access control (interchanges or junctions controlled by traffic lights). Other roads leading to a principal arterial are connected to it through side collector roads.

In this view, CARE's definition stands that a motorway is understood as a

public road with dual carriageways and at least two lanes each way. All entrances and exits are signposted and all interchanges are grade separated. Central barrier or median present throughout the road. No crossing is permitted, while stopping is permitted only in an emergency. Restricted access to motor vehicles, prohibited to pedestrians, animals, pedal cycles, mopeds, agricultural vehicles. The minimum speed is not lower than 50 km/h [31 mph] and the maximum speed is not higher than 130 km/h [81 mph] (except Germany where no speed limit is defined).

Motorways are designed to carry heavy traffic at high speed with the lowest possible number of accidents. They are also designed to collect long-distance traffic from other roads, so that conflicts between long-distance traffic and local traffic are avoided. According to the common European definition, a motorway is defined as "a road, specially designed and built for motor traffic, which does not serve properties bordering on it, and which: (a) is provided, except at special points or temporarily, with separate carriageways for the two directions of traffic, separated from each other, either by a dividing strip not intended for traffic, or exceptionally by other means; (b) does not cross at level with any road, railway or tramway track, or footpath; (c) is specially sign-posted as a motorway and is reserved for specific categories of road motor vehicles." Urban motorways are also included in this definition. However, the respective national definitions and the type of roads covered may present slight differences in different EU countries.

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