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, motorway, and expressway. Other similar terms include throughway or thruway 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.
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, 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 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 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, 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 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
One green or blue symbol 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
;ITE
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 and expressways. Principal arterials may cross through urban areas, serving suburban movements. The traffic is characterized by
high speeds and full or partial access control. 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 and the maximum speed is not higher than .

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: 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; does not cross at level with any road, railway or tramway track, or footpath; 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.

History

The first version of modern controlled-access highways evolved during the first half of the 20th century. The Long Island Motor Parkway on Long Island, New York, opened in 1908 as a private venture, was the world's first limited-access roadway. It included many modern features, including banked turns, guard rails and reinforced concrete tarmac. Traffic could turn left between the parkway and connectors, crossing oncoming traffic, so it was not a controlled-access highway.
Modern controlled-access highways originated in the early 1920s in response to the rapidly increasing use of the automobile, the demand for faster movement between cities and as a consequence of improvements in paving processes, techniques and materials. These original high-speed roads were referred to as "dual highways" and have been modernized and are still in use today.
Italy was the first country in the world to build controlled-access highways reserved for fast traffic and for motor vehicles only. The Autostrada dei Laghi connected Milan to Lake Como and Lake Maggiore, and is now parts of the A8 and A9 motorways. It was devised by Piero Puricelli and was inaugurated in 1924. This motorway, called autostrada, contained only one lane in each direction and no interchanges. The Bronx River Parkway was the first road in North America to utilize a median strip to separate the opposing lanes, to be constructed through a park and where intersecting streets crossed over bridges. The Southern State Parkway opened in 1927, while the Long Island Motor Parkway was closed in 1937 and replaced by the Northern State Parkway and the contiguous Grand Central Parkway. In Germany, construction of the Bonn-Cologne Autobahn began in 1929 and was opened in 1932 by Konrad Adenauer, then the mayor of Cologne. The German Autobahn became the first nationwide highway system.
In Canada, the first precursor with semi-controlled access was The Middle Road between Hamilton and Toronto, which featured a median divider between opposing traffic flow, as well as the nation's first cloverleaf interchange. This highway developed into the Queen Elizabeth Way, which featured a cloverleaf and trumpet interchange when it opened in 1937, and until the Second World War, boasted the longest illuminated stretch of roadway built. A decade later, the first section of Highway 401 was opened, based on earlier designs. It has since gone on to become the busiest highway in the world.
The word freeway was first used in February 1930 by Edward M. Bassett. Bassett argued that roads should be classified into three basic types: highways, parkways, and freeways. In Bassett's zoning and property law-based system, abutting property owners have the rights of light, air and access to highways, but not parkways and freeways; the latter two are distinguished in that the purpose of a parkway is recreation, while the purpose of a freeway is movement. Thus, as originally conceived, a freeway is simply a strip of public land devoted to movement to which abutting property owners do not have rights of light, air or access.

Design

Freeways, by definition, have no at-grade intersections with other roads, railroads or multi-use trails. Therefore, no traffic signals are needed and through traffic on freeways does not normally need to stop at traffic signals. Some countries, such as the United States, allow for limited exceptions: some movable bridges, for instance the Interstate Bridge on Interstate 5 between Oregon and Washington, do require drivers to stop for ship traffic.
The crossing of freeways by other routes is typically achieved with grade separation either in the form of underpasses or overpasses. In addition to sidewalks attached to roads that cross a freeway, specialized pedestrian footbridges or tunnels may also be provided. These structures enable pedestrians and cyclists to cross the freeway at that point without a detour to the nearest road crossing.
Access to freeways is typically provided only at grade-separated interchanges, though lower-standard right-in/right-out access can be used for direct connections to side roads. In many cases, sophisticated interchanges allow for smooth, uninterrupted transitions between intersecting freeways and busy arterial roads. However, sometimes it is necessary to exit onto a surface road to transfer from one freeway to another. One example in the United States is the connection from Interstate 70 to the Pennsylvania Turnpike through the town of Breezewood, Pennsylvania.
Speed limits are generally higher on freeways and are occasionally nonexistent. Because higher speeds reduce decision time, freeways are usually equipped with a larger number of guide signs than other roads, and the signs themselves are physically larger. Guide signs are often mounted on overpasses or overhead gantries so that drivers can see where each lane goes. Exit numbers are commonly derived from the exit's distance in miles or kilometres from the start of the freeway. In some areas, there are public rest areas or service areas on freeways, as well as emergency phones on the shoulder at regular intervals.
In the United States, mileposts usually start at the southern or westernmost point on the freeway. California, Ohio and Nevada use postmile systems in which the markers indicate mileage through the state's individual counties. However, Nevada and Ohio also use the standard milepost system concurrently with their respective postmile systems. California numbers its exits off its freeways according to a milepost system but does not use milepost markers.
In Europe and some other countries, motorways typically have similar characteristics such as:

A typical design speed in the range of
Minimum values for horizontal curve radii around.
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 each, separated by a central median.
An obstacle-free zone varying from, 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 construction of tunnels and overpasses, requiring complex equipment and methods of operation.
Installation of highly efficient road equipment and traffic control devices.