Jump to content

Controlled-access highway

From Wikipedia, the free encyclopedia
(Redirected from Motorway)

The cloverleaf interchange between US 131, M-6 and 68th Street in Cutlerville, Michigan, United States, shows many of the features of controlled-access highways: entry and exit ramps, median strips for opposing traffic, no at-grade intersections and no direct access to properties.
This sign, or some variation thereof, is used to denote controlled-access highways in many countries.
Typical overhead signage on Ontario's King's Highway network featuring an airport pictogram, distances to upcoming interchanges, and lane guidance

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.

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.

Definition standards

[edit]
An aerial view of Finnish national road 3 (E12), a motorway between Tampere and Helsinki in Finland
The west coast motorway E6/E20 in central Gothenburg, Sweden
Autostrada A1 (E35/E45) runs through Italy linking some of the largest cities of the country: Milan, Bologna, Florence, Rome and Naples

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;[6]

One green or blue symbol (like .

The definitions of "motorway" from the OECD[7] and PIARC[8] 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.[9]

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).[9]

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.[10] 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."[11] 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.[12]

History

[edit]
The Italian Autostrada dei Laghi ("Lakes Motorway"; now parts of the Autostrada A8 and the Autostrada A9), the first controlled-access highway ever built in the world,[3][4] in 1925, the year following its inauguration.

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.[13] Traffic could turn left between the parkway and connectors, crossing oncoming traffic, so it was not a controlled-access highway (or "freeway" as later defined by the federal government's Manual on Uniform Traffic Control Devices).

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.

A section of the German Reichsautobahn in 1943, the first nationwide highway system.

Italy was the first country in the world to build controlled-access highways reserved for fast traffic and for motor vehicles only.[3][4] The Autostrada dei Laghi ("Lakes Motorway") 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.[4] 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.[14][15] The Southern State Parkway opened in 1927, while the Long Island Motor Parkway was closed in 1937 and replaced by the Northern State Parkway (opened 1931) and the contiguous Grand Central Parkway (opened 1936). In Germany, construction of the Bonn-Cologne Autobahn began in 1929 and was opened in 1932 by Konrad Adenauer, then the mayor of Cologne.[16] The German Autobahn became the first nationwide highway system.[17]

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.[18] 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.[19][20][21][22] Bassett argued that roads should be classified into three basic types: highways, parkways, and freeways.[19] 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.[19] 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.[19]

Design

[edit]
Highway interchange between the Dolphin Expressway and Palmetto Expressway (Dolphin–Palmetto Interchange) in Greater Miami, Florida, United States
Highway 401 in Southern Ontario, Canada. An example of a collector-express freeway design, the route features four carriageways through Toronto.
The A10 near Orléans, France, showing hard shoulder and emergency telephone. The broken demarcation line for the hard shoulder is specific to France, and serves as a safety reference mark for drivers: the advisory distance from the vehicle ahead is two dashes minimum.

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 (pavements) 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 (left-in/left-out in countries that drive on the left) 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 (notorious for the resulting congestion) is the connection from Interstate 70 to the Pennsylvania Turnpike (Interstate 70 and Interstate 76) through the town of Breezewood, Pennsylvania.[23]

Speed limits are generally higher on freeways and are occasionally nonexistent (as on much of Germany's Autobahn network). 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 (either its terminus or the state line). 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.

Diagram showing lanes and road layout (Irish road markings)

In Europe and some other countries, motorways typically have similar characteristics such as:

  • 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.[24]

Cross sections

[edit]
The Plimoth Patuxet Highway in Massachusetts is a two-lane divided freeway.

A controlled access highway may be two lanes known as a two-lane expressway. They are often undivided, are sometimes built when traffic volumes are low (but may be upgraded later), right-of-way is limited or due to low funding. They may be designed for easy conversion to one side of a four-lane freeway and right of way may already be acquired. (For example, most of the Mountain Parkway in eastern Kentucky is two lanes, but work has begun to make all of it four-lane.) These are often called Super two roads. Several such roads are infamous for a high rate of lethal crashes; an outcome because they were designed for short sight distances (sufficient for freeways without oncoming traffic, but insufficient for the years in service as two-lane road with oncoming traffic). An example of such a "Highway to Hell" was European route E4 from Gävle to Axmartavlan, Sweden. The high rate of crashes with severe personal injuries on that (and similar) roads did not cease until a median crash barrier was installed, transforming the fatal crashes into non-fatal crashes. Otherwise, freeways typically have at least two lanes in each direction; some busy ones can have as many as 16 or more lanes[e] in total.

In San Diego, California, Interstate 5 has a similar system of express and local lanes for a maximum width of 21 lanes on a 2-mile (3.2 km) segment between Interstate 805 and California State Route 56. In Mississauga, Ontario, Highway 401 uses collector-express lanes for a total of 18 lanes through its intersection with Highway 403/Highway 410 and Highway 427.

These wide freeways may use separate collector and express lanes to separate through traffic from local traffic, or special high-occupancy vehicle lanes, either as a special restriction on the innermost lane or a separate roadway, to encourage carpooling. These HOV lanes, or roadways open to all traffic, can be reversible lanes, providing more capacity in the direction of heavy traffic, and reversing direction before traffic switches. Sometimes a collector/distributor road, a shorter version of a local lane, shifts weaving between closely spaced interchanges to a separate roadway or altogether eliminates it.

In some parts of the world, notably parts of the US, frontage roads form an integral part of the freeway system. These parallel surface roads provide a transition between high-speed "through" traffic and local traffic. Frequent slip-ramps provide access between the freeway and the frontage road, which in turn provides direct access to local roads and businesses.[25]

Except on some two-lane freeways (and very rarely on wider freeways), a median separates the opposite directions of traffic. This strip may be as simple as a grassy area, or may include a crash barrier such as a "Jersey barrier" or an "Ontario Tall Wall" to prevent head-on collisions.[26] On some freeways, the two carriageways are built on different alignments; this may be done to make use of available corridors in a mountainous area or to provide narrower corridors through dense urban areas.[citation needed]

Control of access

[edit]

Control of access relates to a legal status which limits the types of vehicles that can use a highway, as well as a road design that limits the points at which they can access it.

Major arterial roads will often have partial access control, meaning that side roads will intersect the main road at grade, instead of using interchanges, but driveways may not connect directly to the main road, and drivers must use intersecting roads to access adjacent land. At arterial junctions with relatively quiet side roads, traffic is controlled mainly by two-way stop signs which do not impose significant interruptions on traffic using the main highway. Roundabouts are often used at busier intersections in Europe because they help minimize interruptions in flow, while traffic signals that create greater interference with traffic are still preferred in North America. There may be occasional interchanges with other major arterial roads. Examples include US 23 between SR 15's eastern terminus and Delaware, Ohio, along with SR 15 between its eastern terminus and I-75, US 30, SR 29/US 33, and US 35 in western and central Ohio. This type of road is sometimes called an expressway.

Non-motorized access on freeways

[edit]

Freeways are usually limited to motor vehicles of a minimum power or weight; signs may prohibit cyclists, pedestrians and equestrians and impose a minimum speed. It is possible for non-motorized traffic to use facilities within the same right-of-way, such as sidewalks constructed along freeway-standard bridges and multi-use paths next to freeways such as the Suncoast Trail along the Suncoast Parkway in Florida.

De Lucht Rest Area on the Dutch A2 - a typical rest area in the Netherlands with services (fuel, refreshments and toilets). The only access is via the highway that it serves.

In some US jurisdictions, especially where freeways replace existing roads, non-motorized access on freeways is permitted. Different states of the United States have different laws. Cycling on freeways in Arizona may be prohibited only where there is an alternative route judged equal or better for cycling.[27] Wyoming, the second least densely populated state, allows cycling on all freeways. Oregon allows bicycles except on specific urban freeways in Portland and Medford.[28]

In countries such as the United Kingdom new motorways require an Act of Parliament to ensure restricted right of way. Since upgrading an existing road (the "King's Highway") to a full motorway will result in extinguishing the right of access of certain groups such as pedestrians, cyclists and slow-moving traffic, many controlled access roads are not full motorways.[29] In some cases motorways are linked by short stretches of road where alternative rights of way are not practicable such as the Dartford Crossing (the furthest downstream public crossing of the River Thames) or where it was not economic to build a motorway alongside the existing road such as the former Cumberland Gap. The A1 is a good example of piece-wise upgrading to motorway standard—as of January 2013, the 639-kilometre-long (397 mi) route had five stretches of motorway (designated as A1(M)), reducing to four stretches in March 2018 with completion of the A1(M) through North Yorkshire.

Construction techniques

[edit]
The Belgrade Urban Motorway, constructed between 1970 and 1977, required demolitions of streets and houses, characteristic of urban motorways. In Novi Beograd, the motorway path was already laid out, requiring no demolitions.

The most frequent way freeways are laid out is by building them from the ground up after obstructions such as forestry or buildings are cleared away. Sometimes they deplete farmland, but other methods have been developed for economic, social and even environmental reasons.

Full freeways are sometimes made by converting at-grade expressways or by replacing at-grade intersections with overpasses; however, in the US, any at-grade intersection that ends a freeway often remains an at-grade intersection. Often, when there is a two-lane undivided freeway or expressway, it is converted by constructing a parallel twin corridor, and leaving a median between the two travel directions. The median-side travel lane of the old two-way corridor becomes a passing lane.

Other techniques involve building a new carriageway on the side of a divided highway that has a lot of private access on one side and sometimes has long driveways on the other side since an easement for widening comes into place, especially in rural areas.

When a third carriageway is added, sometimes it can shift a directional carriageway by 20–60 metres (50–200 ft) (or maybe more depending on land availability) as a way to retain private access on one side that favours over the other. Other methods involve constructing a service drive that shortens the long driveways (typically by less than 100 metres (330 ft)).

Interchanges and access points

[edit]
The High Five Interchange in Dallas, Texas, a stack interchange with elevated entrance and exit ramps connecting Interstate 635 and U.S. Route 75
An aerial view of the Lakalaiva interchange in the Tampere Ring Road between the Highway 3 (E12) and Highway 9 (E63) near city of Tampere

An interchange or a junction is a highway layout that permits traffic from one controlled-access highway to access another and vice versa, whereas an access point is a highway layout where traffic from a distributor or local road can join a controlled-access highway. Some countries, such as the United Kingdom, do not distinguish between the two, but others make a distinction; for example, Germany uses the words Kreuz ("cross") or Dreieck ("triangle") for the former and Ausfahrt ("exit") for the latter. In all cases one road crosses the other via a bridge or a tunnel, as opposed to an at-grade crossing.

The inter-connecting roads, or slip-roads, which link the two roads, can follow any one of a number of patterns. The actual pattern is determined by a number of factors including local topology, traffic density, land cost, building costs, type of road, etc. In some jurisdictions feeder/distributor lanes are common, especially for cloverleaf interchanges; in others, such as the United Kingdom, where the roundabout interchange is common, feeder/distributor lanes are seldom seen.

Motorways in Europe typically differentiate between exits and junctions. An exit leads out of the motorway system, whereas a junction is a crossing between motorways or a split/merge of two motorways. The motorway rules end at exits, but not at junctions. However, on some bridges, motorways, without changing appearance, temporarily end between the two exits closest to the bridge (or tunnel), and continue as dual carriageways. This is in order to give slower vehicles a possibility to use the bridge. The Queen Elizabeth II Bridge / Dartford tunnel at London Orbital is an example of this. London Orbital or the M25 is a motorway surrounding London, but at the last River Thames crossing before its mouth, motorway rules do not apply. (At this crossing the London Orbital is labelled A282 instead.)

A few of the more common types of junction are shown below:[30][31][32]

Follow Lee on X/Twitter - Father, Husband, Serial builder creating AI, crypto, games & web tools. We are friends :) AI Will Come To Life!

Check out: eBank.nz (Art Generator) | Netwrck.com (AI Tools) | Text-Generator.io (AI API) | BitBank.nz (Crypto AI) | ReadingTime (Kids Reading) | RewordGame | BigMultiplayerChess | WebFiddle | How.nz | Helix AI Assistant