Highway

A highway in the broadest sense of the term is any public or private road or other public way on land, including not just major roads but also other public roads and rights of way. In the United States, the term means a major road that carries motor traffic at considerable speed, denoting a controlled-access highway and being a translation for motorway, Autobahn, autostrada, autoroute, etc.
According to Merriam-Webster, the use of the term predates the 12th century. According to Etymonline, "high" is in the sense of "main".
In North American and Australian English, major roads such as controlled-access highways or arterial roads are often state highways. Other roads may be designated "county highways" in the US and Ontario. These classifications refer to the level of government that maintains the roadway. In British English, "highway" is primarily a legal term. Everyday use normally implies roads, while the legal use covers any route or path with a public right of access, including footpaths etc.
The term has led to several related derived terms, including highway system, highway code, highway patrol and highwayman.

Overview

Major highways are often named and numbered by the governments that typically develop and maintain them. Australia's Highway 1 is the longest national highway in the world at over and runs almost the entire way around the continent. China has the world's largest network of highways, followed closely by the United States. Some highways, like the Pan-American Highway or the European routes, span multiple countries. Some major highway routes include ferry services, such as US Route 10, which crosses Lake Michigan.
Traditionally highways were used by people on foot or on horses. Later they also accommodated carriages, bicycles and eventually motor cars, facilitated by advancements in road construction. In the 1920s and 1930s, many nations began investing heavily in highway systems in an effort to spur commerce and bolster national defence.
Major highways that connect cities in populous developed and developing countries usually incorporate features intended to enhance the road's capacity, efficiency, and safety to various degrees. Such features include a reduction in the number of locations for user access, the use of dual carriageways with two or more lanes on each carriageway, and grade-separated junctions with other roads and modes of transport. These features are typically present on highways built as motorways.

Terminology

England and Wales

The general legal definition deals with right of use, not the form of construction; this is distinct from e.g. the popular use of the word in the US. A highway is defined in English common law by a number of similarly worded definitions such as "a way over which all members of the public have the right to pass and repass without hindrance" usually accompanied by "at all times"; ownership of the ground is for most purposes irrelevant, thus the term encompasses all such ways from the widest trunk roads in public ownership to the narrowest footpath providing unlimited pedestrian access over private land.
A highway might be open to all forms of lawful land traffic or limited to specific modes of traffic; usually a highway available to vehicles is also available to foot or horse traffic, a highway available to horse traffic is available to cyclists and pedestrians; but there are exceptional cases in which a highway is only available to vehicles, or is subdivided into dedicated parallel sections for different users.
A highway can share ground with a private right of way for which full use is not available to the general public: for example farm roads which the owner may use for any purpose but for which the general public only has a right of use on foot or horseback. The status of highway on most older roads has been gained by established public use, while newer roads are typically dedicated as highways from the time they are adopted. In England and Wales, a public highway is also known as "The King's Highway".
The core definition of a highway is modified in various legislation for a number of purposes but only for the specific matters dealt with in each such piece of legislation. This is typically in the case of bridges, tunnels and other structures whose ownership, mode of use or availability would otherwise exclude them from the general definition of a highway. Recent examples include toll bridges and tunnels which have the definition of highway imposed upon them to allow application of most traffic laws to those using them but without causing all of the general obligations or rights of use otherwise applicable to a highway.
Limited access highways for vehicles, with their own traffic rules, are called "motorways" in the UK.

Scotland

is similar to English law with regard to highways but with differing terminology and legislation. What is defined in England as a highway will often in Scotland be what is defined by s.151 Roads Act 1984 simply as a road, that is:

"any way over which there is a public right of passage and includes the road’s verge, and any bridge over which, or tunnel through which, the road passes; and any reference to a road includes a part thereof"

The word highway is itself no longer a statutory expression in Scots law but remains in common law.

United States

In American law, the word "highway" is sometimes used to denote any public way used for travel, whether a "road, street, and parkway"; however, in practical and useful meaning, a "highway" is a major and significant, well-constructed road that is capable of carrying reasonably heavy to extremely heavy traffic. Highways generally have a route number designated by the state and federal departments of transportation.
California Vehicle Code, Sections 360, 590, define a "highway" as only a way open for use by motor vehicles, but the California Supreme Court has held that "the definition of 'highway' in the Vehicle Code is used for special purposes of that act" and that canals of the Los Angeles neighborhood of Venice are "highways" that are entitled to be maintained with state highway funds.

History

Large scale highway systems developed in the 20th century as automobile usage increased. The first United States limited-access road was constructed on Long Island, New York, and known as the Long Island Motor Parkway or the Vanderbilt Motor Parkway. It was completed in 1911. 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.
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 , the first built in the world, connecting Milan to Lake Como and Lake Maggiore, and now parts of the A8 and A9 highways, was devised by Piero Puricelli and was inaugurated in 1924. This highway, called autostrada, contained only one lane in each direction and no interchanges.
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. Soon the Autobahn was the first limited-access, high-speed road network in the world, with the first section from Frankfurt am Main to Darmstadt opening in 1935.
In the US, the Federal Aid Highway Act of 1921 enacted a fund to create an extensive highway system. In 1922, the first blueprint for a national highway system was published. The Federal Aid Highway Act of 1956 allocated $25 billion for the construction of the Interstate Highway System over a 20-year period.
In Great Britain, the Special Roads Act 1949 provided the legislative basis for roads for restricted classes of vehicles and non-standard or no speed limits applied ; in terms of general road law this legislation overturned the usual principle that a road available to vehicular traffic was also available to horse or pedestrian traffic as is usually the only practical change when non-motorways are reclassified as special roads. The first section of motorway in the UK opened in 1958 and then in 1959 the first section of the M1 motorway.

Design

Classification

In the United States, Federal Highway Administration classifies highways into the following categories:

Principal arterial, which can be further recognized in urban and rural forms
Minor arterial
Collector, which can be further recognized in urban and rural forms
Local

This classification is based on the concept of accessibility and mobility. High mobility roads are considered arterial roads, roads with high accessibility are considered local roads, while those balancing between mobility and accessibility are called collectors.
Similarly in Europe, the European Commission defines the road categories as:

Arterial / through traffic flow routes are roads with a flow function, which encourage efficient throughput of motor vehicles and can be further divided to primary and local arterials.
Distributor roads are roads with an area distribution function which permits transition from residential, industrial, recreational areas to scattered destinations. These roads can be further divided to primary and local distributors.
Access roads are roads with an access function, allowing actual access to road-side properties.
Metrics

There are three speed performance measures for highways:

Free-flow speed: a speed selected by most drivers when they are driving alone on the subject highway with green lights, but facing other restrictions such as pedestrians, parking, and road geometrics. Free-flow speed reflects the driving "environment" and may vary by the time of the day.
Running speed / average running speed: average vehicle speed while in motion, which might be slower than free flow speed.
Average travel speed: actual traveling speed, a metric used for determining the subject highway's level of service.

An additional metric involves delays. Control delays are delays caused by traffic control devices. According to Highway Capacity Manual, control delay at a signalized intersection may be calculated as a sum of uniform delay, incremental delay, and initial queue delay:
where:

= delay due to pre-existing queue before the next arrival, seconds per vehicle
= cycle length, s
= effective green time, s
= volume-to-capacity ratio
= progression adjustment factor, to account for the timing of traffic arriving in platoon, and decreases as the platoon arrival performance increases
= duration of analysis period, hour
= incremental delay adjustment for actuated control
= incremental delay adjustment for upstream signals filtering and equals to 1.0 when the intersection is isolated
= capacity of the lane group, vehicle per hour