A dual carriageway (North American English

North American English

North American English is the variety of the English language of North America, including that of the United States and Canada. Because of their shared histories and the similarities between the pronunciation, vocabulary and accent of American English and Canadian English, the two spoken languages...

: divided highway) is a class of highway

Highway

A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...

 with two carriageways for traffic travelling in opposite directions separated by a central reservation

Central reservation

On divided roads, such as divided highways or freeways/motorways, the central reservation , median, parkway , median strip or central nature strip is the area which separates opposing lanes of traffic...

 (North American English: median). Roads with two or more carriageways which are designed to higher standards with limited access

Limited-access road

A limited-access road known by various terms worldwide, including limited-access highway, dual-carriageway and expressway, is a highway or arterial road for high-speed traffic which has many or most characteristics of a controlled-access highway , including limited or no access to adjacent...

 and grade separation are generally classed as motorways, freeways, etc., rather than dual carriageways. A road without a central reservation is a single carriageway

Single carriageway

A single carriageway is a road with 1, 2 or more lanes arranged within a single carriageway with no central reservation to separate opposing flows of traffic. Two-lane road or two-lane highway are single carriageway with one lane for each direction...

 (North American English undivided highway) regardless of the number of lanes. Dual carriageways have improved road traffic safety over single carriageway

Single carriageway

A single carriageway is a road with 1, 2 or more lanes arranged within a single carriageway with no central reservation to separate opposing flows of traffic. Two-lane road or two-lane highway are single carriageway with one lane for each direction...

s and typically have higher speed limits as a result. In some places, express lanes and local/collector lanes are used within a local-express-lane system

Local-express lanes

A Local-express lane system is an arrangement of roadways within a major highway providing one of more roadways for express lanes with a limited number of entrances and exits and also separate roadways for local or collector lanes which provide access to all interchanges...

 to provide more capacity and to smoothe traffic flows for longer-distance travel.

History

A very early (perhaps the first) example of a dual carriageway was the Via Portuensis

Via Portuensis

Via Portuensis was an ancient Roman road, leading to the Portus constructed by Claudius on the right bank of the Tiber, at its mouth. It started from the Pons Aemilius, and the first part of its course is identical with that of the Via Campana...

, built in the first century by the Roman emperor Claudius

Claudius

Claudius , was Roman Emperor from 41 to 54. A member of the Julio-Claudian dynasty, he was the son of Drusus and Antonia Minor. He was born at Lugdunum in Gaul and was the first Roman Emperor to be born outside Italy...

 between Rome

Rome

Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...

 and its port Ostia at the mouth of the Tiber

Tiber

The Tiber is the third-longest river in Italy, rising in the Apennine Mountains in Emilia-Romagna and flowing through Umbria and Lazio to the Tyrrhenian Sea. It drains a basin estimated at...

.

In 1907 the Long Island Motor Parkway

Long Island Motor Parkway

The Long Island Motor Parkway , also known as the Vanderbilt Parkway and Motor Parkway, was the first roadway designed for automobile use only. It was privately built by William Kissam Vanderbilt with overpasses and bridges to remove intersections...

 opened and roughly 20% of it featured a semi-dual-carriageway design. The New York City

New York City

New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...

 Belt Parkway

Belt Parkway

The Belt System is a series of connected limited-access highways that form a belt-like circle around the New York City boroughs of Brooklyn and Queens. The system comprises four officially separate parkways; however, three of the four are signed as the Belt Parkway...

 system, which was built between 1907 and 1934, also pioneered the same design. However the majority of it featured concrete or brick railings as lane dividers instead of grass medians.

In 1924 the first Italian autostrada

Autostrade of Italy

The Autostrada is the Italian national system of motorways. The total length of the system is about 6,400 km. In North and Central Italy this is mainly as tollways, with the biggest portion in concession to the Atlantia group which operates some 3,408 km...

was opened running 55 km (34.2 mi) from Milan to Varese. It featured a broad road bed and did not feature lane dividers except near cities and through the mountains.

The London end of the Great West Road became Britain's first dual carriageway when it was opened in 1925 by King George V.

In 1927 the Rome bypass was opened. It ran 92 km (57.2 mi) bypassing Rome to the east. Almost the entire length featured a dual-carriageway design. In the early 1930s it was extended southward all the way to Naples

Naples

Naples is a city in Southern Italy, situated on the country's west coast by the Gulf of Naples. Lying between two notable volcanic regions, Mount Vesuvius and the Phlegraean Fields, it is the capital of the region of Campania and of the province of Naples...

 and northward to Florence. Most of the original routing was destroyed by the Allies in the World War II

World War II

World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

.

By 1930 several US and European cities had built dual-carriageway highways, mostly to control traffic jams and/or to provide bypass routes for traffic.

In 1932 the first German autobahn opened between Cologne and Bonn. It ran 21 km (13 mi) and became a precedent for future highways. Although it, like the first autostrada, did not feature a dual-carriageway design, it inspired the mass construction of future high-speed roadways.

During the 1930s, Germany, Italy, and the Soviet Union began construction of a network of dual carriageway expressways. By 1942, Germany had over 3200 km (1,988.4 mi) of dual carriageway roads, Italy had nearly 1300 km (807.8 mi), and the Soviet Union had 400 km (248.5 mi).

What may be the world's first long-distance intercity dual carriageway/freeway is the Queen Elizabeth Way

Queen Elizabeth Way

The Queen Elizabeth Way, commonly abbreviated as the QEW, is a 400-Series highway in the Canadian province of Ontario. The freeway links Buffalo, New York and the Niagara Peninsula with Toronto. It begins at the Peace Bridge in Fort Erie and travels around the western shore of Lake Ontario, ending...

 in Southern Ontario

Southern Ontario

Southern Ontario is a region of the province of Ontario, Canada that lies south of the French River and Algonquin Park. Depending on the inclusion of the Parry Sound and Muskoka districts, its surface area would cover between 14 to 15% of the province. It is the southernmost region of...

 in Canada

Canada

Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...

, initially linking the large cities of Toronto

Toronto

Toronto is the provincial capital of Ontario and the largest city in Canada. It is located in Southern Ontario on the northwestern shore of Lake Ontario. A relatively modern city, Toronto's history dates back to the late-18th century, when its land was first purchased by the British monarchy from...

 and Hamilton

Hamilton, Ontario

Hamilton is a port city in the Canadian province of Ontario. Conceived by George Hamilton when he purchased the Durand farm shortly after the War of 1812, Hamilton has become the centre of a densely populated and industrialized region at the west end of Lake Ontario known as the Golden Horseshoe...

 together by 1939, with construction on this stretch of the present-day Queen Elizabeth Way beginning in 1936 as "Middle Road".

Opened to traffic in 1940, the 160 miles (257.5 km) long Pennsylvania Turnpike

Pennsylvania Turnpike

The Pennsylvania Turnpike is a toll highway system operated by the Pennsylvania Turnpike Commission in the Commonwealth of Pennsylvania, United States. The three sections of the turnpike system total . The main section extends from Ohio to New Jersey and is long...

 was the first rural dual carriageway built in the United States. By 1955 several states had built dual carriageway freeways and turnpikes and in 1957 the Interstate Highway System

Interstate Highway System

The Dwight D. Eisenhower National System of Interstate and Defense Highways, , is a network of limited-access roads including freeways, highways, and expressways forming part of the National Highway System of the United States of America...

 began. Completed in 1994, the major highway system links all the major cities of the United States.

United Kingdom

In the UK

United Kingdom

The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

, although the term dual carriageway applies to any road with physically separated lanes, it is frequently used as a descriptive term for major route

Highway

A highway is any public road. In American English, the term is common and almost always designates major roads. In British English, the term designates any road open to the public. Any interconnected set of highways can be variously referred to as a "highway system", a "highway network", or a...

s built in this style. Such major dual carriageways usually have two lanes of traffic in each direction, with the lane nearest the centre being reserved for overtaking. Occasionally dual carriageways have only one lane in each direction, or more than two lanes each way (usually to permit easier overtaking of slower uphill traffic). Different speed limits apply on dual carriageway sections from those that apply on single carriageway

Single carriageway

A single carriageway is a road with 1, 2 or more lanes arranged within a single carriageway with no central reservation to separate opposing flows of traffic. Two-lane road or two-lane highway are single carriageway with one lane for each direction...

 sections of the same class of road, except in cities and built-up areas where the dual carriageway is more of a safety measure, often intended to prevent pedestrian

Pedestrian

A pedestrian is a person traveling on foot, whether walking or running. In some communities, those traveling using roller skates or skateboards are also considered to be pedestrians. In modern times, the term mostly refers to someone walking on a road or footpath, but this was not the case...

s from crossing a busy road.

When first constructed, many dual carriageways - including the first motorways - had no crash or other barriers in the central reservation. Hence in the event of delays on the road, or if a driver missed his exit, there was a widespread problem of drivers making a U-turn onto the other carriageway; many accidents were caused as a result of their misjudging the speed of approaching traffic on the other carriageway when doing so. The majority of dual carriageway roads now have barriers. Some are heavy concrete obstructions which can have the effect of bouncing a vehicle back into the path of other traffic; others are made from steel ropes mounted on moderately weak posts, where the rope cuts into the vehicle body to slow the vehicle while keeping it against the barrier until it has stopped. Often on urban dual carriageways where the road has been converted from a four-lane single carriageway the central reservation will be nominal and often just a small steel divider to save space.

Turning right (that is, across the line of traffic heading in the opposite direction) is usually permitted only at specific locations. Often the driver will be required to turn left (away from the dual carriageway) in order to loop around to an access road that permits crossing the major road. Roundabout

Roundabout

A roundabout is the name for a road junction in which traffic moves in one direction around a central island. The word dates from the early 20th century. Roundabouts are common in many countries around the world...

s on dual carriageways are relatively common, especially in cities or where the cost of a grade-separated junction would be prohibitive. Where space is even more limited, intersections may be controlled by traffic lights. Smaller residential roads adjoining urban dual carriageways may be blocked off at one end in an attempt to limit the number of junctions on a dual carriageway, often other roads may pass over or under the dual-carriageway without an intersection.

A dual carriageway with grade-separated junctions and which meets other requirements may be upgraded to motorway standard, denoted as an (M) added after the road number (e.g. "A1(M)" or "A38(M)"). Unlike in the Republic of Ireland

Republic of Ireland

Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

, there is no official terminology for 'high-quality dual carriageways'. Many roads such as the A1, the A14, the A19

A19 road

The A19 is a major road in England running approximately parallel to and east of the A1 road, although the two roads meet at the northern end of the A19, the two roads originally met at the southern end of the A19 in Doncaster but the old route of the A1 was changed to the A638. From Sunderland...

 and the A42

A42 road

The A42 is a major trunk road in the East Midlands region of the United Kingdom. It links junction 23A of the M1 motorway to junction 11 of the M42 motorway. The A42 is in effect a continuation of the M42, and its junctions are numbered accordingly....

 are built to a high quality, with grade-separated junctions, full barriers at roadside and central reservations and, in some cases, three lanes of traffic. They may still fall short of motorway standard in terms of the height of overpasses or the quality of intersecting junctions.

Speed limits

The national speed limit applies on dual carriageways (unless it is in a 'built-up area', or a lower limit is posted), which is as follows:

National speed limits on dual carriageways in the UK

Type of vehicle	Speed limit
Car Automobile An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor... , motorcycle Motorcycle A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...  or a car-based van Van A van is a kind of vehicle used for transporting goods or groups of people.In British English usage, it can be either specially designed or based on a saloon or sedan car, the latter type often including derivatives with open backs...  up to 2 metric tonnes	70 mi/h
Car with caravan Travel trailer A travel trailer or caravan is towed behind a road vehicle to provide a place to sleep which is more comfortable and protected than a tent . It provides the means for people to have their own home on a journey or a vacation, without relying on a motel or hotel, and enables them to stay in places...  or trailer	60 mi/h
Bus Bus A bus is a road vehicle designed to carry passengers. Buses can have a capacity as high as 300 passengers. The most common type of bus is the single-decker bus, with larger loads carried by double-decker buses and articulated buses, and smaller loads carried by midibuses and minibuses; coaches are...  or coach Coach (vehicle) A coach is a large motor vehicle, a type of bus, used for conveying passengers on excursions and on longer distance express coach scheduled transport between cities - or even between countries...  up to 12 m long	60 mi/h
Goods vehicle up to 7.5 t	60 mi/h
Goods vehicle over 7.5 t	50 mi/h

A dual carriageway in a built up area will have a statutory speed limit of 30 mi/h unless otherwise sign-posted. It is common for such urban dual carriageways to have an increased speed limit of 40 mi/h. A built up road is indicated by the presence of street lights, on lit dual carriageways that are not considered to be in a built-up area, the speed limit will be clarified with intermittent signs.

Ireland

Although in the Republic of Ireland

Republic of Ireland

Ireland , described as the Republic of Ireland , is a sovereign state in Europe occupying approximately five-sixths of the island of the same name. Its capital is Dublin. Ireland, which had a population of 4.58 million in 2011, is a constitutional republic governed as a parliamentary democracy,...

 the term dual carriageway technically applies to any road with physically separated lanes, it is usually used only to refer to those route sections that do not have a motorway designation. Most often it is national roads (roads with a route number prefix of N; e.g. N8) that are built as or upgraded to dual carriageway. A number of non-national roads (for example, regional road

Regional road

A regional road in Ireland is a class of road not forming a major route , but nevertheless forming a link in the national route network. There are over 11,600 kilometres of regional roads. Regional roads are numbered with three digit route numbers, prefixed by "R" A regional road in Ireland is a...

s) are dual carriageway, for example in urban areas near or in cities, or where the road was formerly part of a national route.

Dual carriageways of this class differ from motorways in a number of ways. The hard shoulder is demarcated with a dashed yellow line (as opposed to an unbroken yellow line on motorways). The standard speed limit of 100 km/h (62 mph) for national routes usually applies (by default the limit is 80 km/h (50 mph) for non-national roads, even if dual carriageway). Local authorities have the power to apply a limit of up to 120 km/h (75 mph) as used on most motorways (The High Quality Dual Carriageway section of the N1 between the end of the M1 and the border with Northern Ireland

Northern Ireland

Northern Ireland is one of the four countries of the United Kingdom. Situated in the north-east of the island of Ireland, it shares a border with the Republic of Ireland to the south and west...

 and the N25/N22 Ballincollig Bypass in Cork are the only route sections with such special limits). Traffic lights and junctions are permitted at grade on dual carriageways. For older sections of dual carriageway, this has resulted in fewer flyover junctions. Newer dual carriageway sections are usually near motorway standard, with grade-separated junctions, but may not be designated as motorways due to the need to preserve access to adjoining property or to the absence of a non-motorway alternative route. Also, dual carriageways that are not motorway classified do not need to be equipped with emergency phones.

Motorway restrictions only apply to motorway sections, rather than all dual carriageway sections of national roads (these are signposted with the N prefix on the route number, rather than M). Some national secondary road

National secondary road

A national secondary road is a category of road in Ireland. These roads form an important part of the national route network, but are secondary to the main arterial routes which are classified as national primary roads. National secondary roads are designated with route numbers higher than those...

s, and regional roads in particular often have houses, schools and other developments fronting on to them. Less important national primary road

National primary road

A national primary road is a road classification in the Republic of Ireland. National primary roads form the major routes between the major urban centres. There are over 2,700km of national primary roads. This category of road has the prefix "N" followed by one or two digits...

s, and older sections not yet upgraded may also feature such developments built before the introduction the Irish Planning system in 1964. Today Irish planning policy prohibits such development on National Primary or National Secondary roads where the speed limit exceeds 60 km/h (37 mph). This policy results from concerns expressed by the National Roads Authority. However, a local authority is not obliged to implement this policy and can disregard this policy at it own discretion. This would usually only occur in exceptional circumstances or where planners are over ruled by elected councillors using section 140 of the Local Government Act 2001. Accordingly, hard shoulders are included wherever feasible to provide for the resulting pedestrian and cyclist traffic, and are present on much of the national route network. These hard shoulders may also be used as running lanes by motorised traffic under certain conditions.

Until 2004/2005, many motorways and dual carriageways in Ireland did not have crash barriers in the central reservation, the policy being to use a wider median instead. Crash barriers are now mandatory for such routes, and wire cabling or full crash barriers (depending on whether or not the route is a motorway, and median width) have been fitted to existing routes.

three major types of dual carriageway are being built on national road schemes in the Republic of Ireland:

• High Quality Dual Carriageways (HQDC) - these are being built mainly on the major inter-urban routes, to full motorway standard but without motorway regulations. The Roads Act 2007 allows for these roads to be redesignated as motorways by ministerial order. Many of the sections of HQDC on the major inter-urban routes have been redesignated as motorways and full motorway regulations will apply when the redesignations come into effect.
• Standard dual carriageway of the traditional type is mainly planned for schemes on the N11 road, the N18 road and the N25 road
  N25 road
  The N25 road is a national primary road in Ireland, forming the route from Cork to Rosslare Europort via Waterford City. The road is part of the E30 European route and a short section is also part of the E01 European route...
  
  . Plans for this type of dual carriageway on the N20 road have been superseded by newer plans to build a motorway, the M20, to replace most of this route. Traditionally this type of dual-carriageway had a mixture of at grade junctions (including roundabouts), grade separated junctions, and median crossings. Nowadays they are similar to HQDCs, but minor at grade exits - generally left turn only - are allowed and the design speed (by Irish standards) is only 100 km/h. Median crossings and roundabouts are no longer generally found on these schemes. An example of a standard dual carriageway scheme, opened in 2006, is the Ennis
  Ennis
  Ennis is the county town of Clare in Ireland. Situated on the River Fergus, it lies north of Limerick and south of Galway. Its name is a shortening of the original ....
  
   bypass although this road has grade separated junctions and no median crossings. This route has now been upgraded to motorway status.
• 2+2 road
  2+2 road
  A 2+2 road is a specific type of dual-carriageway being built in Ireland and Sweden, consisting of two lanes in each direction separated with a steel cable barrier. They do not have hard shoulders. Junctions are at-grade roundabouts and minor roads cross under or over the mainline without...
  
  s - officially these roads are designated as Type 2 dual carriageways by the National Roads Authority
  National Roads Authority
  The National Roads Authority is a state body in the Republic of Ireland, responsible for the national road network. The NRA was established as part of the Roads Act 1993 and commenced operations on 23 December 1993 in accordance with S.I. 407 of 1993.County councils remain responsible for local...
  
   (NRA). They will be created by widening existing roads or building new roads, and will have two lanes in each direction with a steel cable barrier
  Cable barrier
  Cable barrier, sometimes referred to as guard cable, is a type of roadside or median barrier. It consists of steel wire ropes mounted on weak posts. As is the case with any roadside barrier, its primary purpose is to prevent a vehicle from leaving the traveled way and striking a fixed object or...
  
   in the middle but no hard shoulder. Most junctions will be at grade. With the exception of the restricted median width and the lack of lay-bys, this type of dual carriageway is similar to many dual carriageways found in the UK. The first 2+2 scheme (and the only example as of 2008), the N4 Dromod
  Dromod
  Dromod is a village in County Leitrim, Ireland. Dromod is a noted fishing village on Loughs Bofin and Boderg, which are threaded by the River Shannon....
  
   Roosky
  Roosky
  Roosky or Rooskey is a village on the River Shannon in County Roscommon, Ireland in the northern midlands of Ireland, near the point where counties Leitrim, Longford, and Roscommon meet. The N4 road from Dublin to Sligo passes by the Leitrim side of the village.- History :Roosky has had a...
  
   bypass, opened on 7 December 2007.
• 2+1 road
  2+1 road
  2+1 road is a specific category of three-lane road, consisting of two lanes in one direction and one lane in the other, alternating every few kilometres, and separated usually with a steel cable barrier. Traditional roads of at least width can be converted to 2+1 roads and reach near-motorway...
  
  s - officially these roads are designated as Type 3 dual carriageways by the NRA. They have two lanes in one direction and one lane in the other, alternating every few kilometres, and usually separated with a steel cable barrier. Sections of 2+1 road have been built on the N20 and the N2. In July 2007, the NRA announced that it would no longer build 2+1 roads and 2+2 roads will be built instead.

Germany

In Germany the term "Schnellstraße" (expressway) refers to streets that allow for higher speed traffic than is common on other streets which in turn requires them to have a dual carriageway in most cases. A special exception is the 2+1 road

2+1 road

2+1 road is a specific category of three-lane road, consisting of two lanes in one direction and one lane in the other, alternating every few kilometres, and separated usually with a steel cable barrier. Traditional roads of at least width can be converted to 2+1 roads and reach near-motorway...

 system in some rural areas that are also referred to as expressways (three lanes on a single carriageway where bypassing on the lane of the opposite direction is prohibited so that speed restriction is not required to increase safety - they are generally built to a 100 or 120 km/h traffic standard). This is based on the definition of expressways as having an increased amount of grade-separated sections. Technically a dual carriageway with central reservation is the legal foundation that no blank speed limit exists - comparable to the German Autobahn - but expressways are factually always given speed limit signs.

Expressways however can be upgraded to motorway standard which is colloquially referred to as "Gelbe Autobahn" (yellow motorway) because they have the same technical standard of the German autobahn but they use black on yellow signs instead of the white on blue signs on the Autobahn motorway network. These are generally high speed arterial roads of larger cities and important streets inside a federal state that do not connect major cities so that they do not fall under the federal budgeting program for the Autobahn network. The federal road Bundesstraße 27 is an example where about half of its length is upgraded to a high speed motorway standard. Some of these non-Autobahn motorways do not have an actual speed limit (design speed 130 km/h).

Exit signs.