Dual carriageway

A very early (perhaps the first) example of a dual carriageway was the Via Portuensis, built in the first century by the Roman emperor Claudius between Rome and its harbor of Portus.

The route between the city and the port experienced a great deal of commercial and pedestrian traffic, as Portus served as the primary avenue for the grain shipments of the Cura Annonae into Rome, as well as transporting the majority of goods imported from across the Mediterranean world.

[1] One claim for the first divided highway in the United States was Savery Avenue in Carver, Massachusetts, first built in 1860, where the two roadways were separated by a narrow strip of trees down the middle.

What may have been the world's first long-distance intercity dual carriageway/freeway was the Queen Elizabeth Way in Southern Ontario in Canada, initially linking the large cities of Toronto and Hamilton 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-mile-long (260 km) Pennsylvania Turnpike was the first rural dual carriageway built in the United States.

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

Unlike in Ireland, there was no official terminology for 'high-quality dual carriageways' until April 2015, when in England a new standard was set to designate certain high-quality routes formally as "Expressways".

[7] Many roads such as the A1, the A14, the A19 and the A42 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 hard shoulders, the height of overpasses or the quality of intersecting junctions.

Although in Ireland 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.

Less important national primary roads, and older sections not yet upgraded may also feature such developments built before the introduction the Irish Planning system in 1964.

This would usually only occur in exceptional circumstances or where planners are overruled 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.

Until 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.

The federal road Bundesstraße 27 is an example where about half of its length is upgraded to a high speed motorway standard.

At the moment some (blue) motorways have been taken out of the Autobahn network programme but still have the blue signs (e. g. the B 59, formerly A 540 near Grevenbroich); and on the other hand some former non-Autobahn (yellow) motorways have been added to Autobahn budgeting but the signs have not been changed either (e. g. parts of the B 6, now A 36 in the north of the Harz highland area in Saxony-Anhalt).

Modern autovías are two carriageways built from scratch, leaving the old road they replace as an alternative route for pedestrians, bicycles and other non-motorized vehicles.

Private properties may have direct access to an autovía, as well as bus stops and gas stations in the hard shoulders.

In the United States, this type of road may be called a divided highway, boulevard, parkway, expressway, freeway, or interstate, and has a grassy median or Jersey barrier separating the traffic directions.

One privately run toll road in Texas, SH 130, has the highest speed limit in the United States at 85 miles per hour (137 km/h).

Frequently in the U.S. the two carriageways are separated by some distance (wide medians with small forests or even hills in them), but drivers can always tell whether the roadway is two-way or one-way—and, if one-way, the direction in which the traffic flows—by looking at the striping coloration.

Unlike some other countries, divided dual carriageways in Canada are seldom equipped with traffic circles, roundabouts, or rotaries as alternatives to stoplights.

However, due to a lack of funding elsewhere, partial controlled-access "expressways" and limited-mobility divided arterial roads are more common in the western provinces where there are no specially numbered systems of freeways.

Some partial limited-access divided highways such as the Hanlon Parkway and Black Creek Drive have stop-controlled at-grade intersections and private entrances, but have sufficient right-of-way to convert them to full freeways with interchanges if traffic warrants.

There are also RIRO expressways, such as Highway 11 and a portion of Highway 35, which are not full freeways since they allow access to existing properties, but traffic speeds are faster than regular roads due to a median barrier preventing left turns (motorists have to use a "turnabout" overpass to access exits on the opposing direction).

VicRoads, the agency responsible for highways in the state of Victoria, has often declared rural limited-access dual carriageways as freeways.

[14] Furthermore, VicRoads applies the M designation to these roads in alpha-numeric route numbers, where most other states will only do so if access is completely controlled.

Dual carriageways exist in and around the major capital cities however there are currently several road projects under construction have now been completed, creating roughly 2,000 kilometres of continuous dual carriageway from Geelong in Victoria to Curra in South East Queensland except for one 14 kilometre section of the Pacific Highway through Coffs Harbour.

In the stretch between the 2 largest cities in the country, São Paulo and Rio de Janeiro, the highway was duplicated in 1967.

Chile doesn't just expand the highway after the city of Caldera because in this part of the country, it enters the Atacama Desert, where there is low traffic of vehicles.