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 13 metres width can be converted to 2+1 roads and reach near-motorway safety levels at a much lower cost than an actual conversion to motorway or dual carriageway. Denmark and Sweden have been building 2+1 roads since the 1990s.

Introduction of 2+1 in Ireland

In the Republic of Ireland, 2+1 refers to a particular class of divided carriageway that for the most part has three lanes, officially called Type 3 Dual CarriagewaysFact|date=April 2008. Such roads alternate between two lanes on one side, and one lane on the other; although there is only one lane in each direction for short distances at changeover points, and for the mainline where turning lanes are present on one or both sides of the carriageway approaching junctions. The road type is distinct from ordinary two lane single carriageway roads (S2) or wide two lane roads (WS2) that have sporadic additional lanes on one side for hills (climbing lanes) or right turns at junctions.

Many national primary roads in the Republic were upgraded in the 1990s and 2000s to "wide two lane" road (two lane road with space for three lanes, in addition to hard shoulders) to allow more space for overtaking (a very common maneuver in a country that had little dual carriageway until the early 2000s). However, due to the deceptive perception of safety given by such roads, many future upgrade projects are intended to be constructed as 2+1 road where traffic volume suits.

A pilot installation was used on the N20 near Mallow, County Cork. As of 2006, the National Roads Authority had decided to install 2+1 on other routes; including some under construction in 2006. As of 2006, existing 2+1 roads in the Republic of Ireland use a central crash barrier of similar design to that installed from 2004 onwards for straight sections of dual-carriageways and motorways (prior to 2004, only narrow median and obstacles such as flyover supports and embankments used crash barriers). These barriers consist of closely spaced poles, fixed below ground, carrying three high-tension thick wound cables. There are interim plans for maintaining these barriers daily, as they require prompt attention in the event of their being damaged in an accident.

In July 2007, it was announced that the National Roads Authority would no longer be building 2+1 roads, and instead replacing them with 2+2 roads (officially known as Type 2 Dual Carriageways [http://www.nra.ie/RoadSchemeActivity/WaterfordCountyCouncil/N25KilmacthomasBypass22/SchemeName,9948,en.html] )- at grade dual-carriageways with a narrow median and no hard shoulders. A large portion of the country's 'N' road network will be upgraded to either motorway or dual carriageway by 2013-5. Existing 2+1 pilot schemes will be left intact for now. Ordinary two lane, and even wide two lane, will still be used on routes requiring lower capacity. High quality dual carriageway/motorway is being installed on the major high capacity national primary roads.

Northern Ireland

In the late 1950's when the Northern Ireland motorway network was being planned it was originally intended that the M4 would run from Sprucefield (where it connects with the M1 near Belfast) all the way to Enniskillen however in the end the M4 terminated near Dungannon with the A4 continuing as a 2 lane highway via Enniskillin to the border at Belcoo. However recently short streaches of the A4 route between Enniskillen and Dungannon have been converted to 2+1 layout.

weden

In Sweden, many 13 meters wide road have been built, especially in the period 1955-1980. These have two 3.5 m wide lanes, and two 3 m wide shoulders, in the beginning planned as emergency strip. Cars weren't as reliable then.

Around 1990 the idea emerged to build fences in the middle of them and to have 2+1 lane. This would be a cheap way of increasing traffic safety, since these roads have had a bad safety record. The width invites to high speed. Some people were for example overtaking against meeting traffic assuming meeting cars would go to the side. The roads are a little narrow for 3 lanes, but tests were made on a few roads. It turned out that not only safety improved, but it was also easier to overtake than before, since the 2-lane parts give safe overtaking opportunities. After year 2000 more than 1000 km of road in Sweden have been converted from wide ordinary road into 2+1-road. [Swedish Wikipedia]

North America

In North America there are similar 2-lane highways with occasional segments where a passing lane is added to only one side at a time (2:1 lane ratio), usually without a barrier between the directions. These are often called climbing lanes as they allow drivers to pass slow moving trucks as they ascend a hill or mountain. The 2+1 roads in North America are often similar to having a 3-lane reversible lane road, but with a yield: right-of-way setup where the oncoming side has a sign stating "yield to oncoming traffic".

This is a common set up in Canada especially in British Columbia where traffic volumes are lower and terrain extremely mountainous making expanding roads expensive if not impossible. The same design can be also found on Highway 8 in New Brunswick Canada, running between Miramichi and Bathurst.

ee also

*Reversible lane

References

*" [http://www.trm.dk/sw9212.asp 2+1 roads - Danish experiences] ", report from Danmarks Transportforskning, November 16, 2001
* [http://www.nra.ie/ National Roads Authority] :
** [http://www.nra.ie/PublicationsResources/DownloadableDocumentation/RoadDesignConstruction/file,1317,en.pdf Interim Advice Note on Road Link Design for 2+1 roads] (PDF 4.7MB)
** [http://www.nra.ie/mapping// Major Road Schemes in Ireland 2008 update]