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 (43 ft) 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.

In Ireland, a 2+1 road was trialled on a short section of the N20 near Mallow, County Cork and the N2 near Castleblayney, County Monaghan. Following the pilot the National Roads Authority announced in July 2007 that 2+1 roads were unsuitable and that new lower capacity trunk routes would instead be built as 2+2 roads (officially known as Type 2 Dual Carriageways [1] ) - at grade dual-carriageways with a narrow median and no hard shoulder.

In Sweden, many 13-metre-wide (43 ft) roads have been built, especially in the period 1955–1980. These have two 3.5 metres (11 ft) wide lanes, and two 3 metres (9.8 ft) wide shoulders, in the beginning planned as emergency strip, due to the relative unreliability of autos of that period.

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 high speeds. 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 trials were carried on a few roads. It turned out that not only did safety improve, but it was also easier to overtake than before as the 2-lane sections provide safe overtaking opportunities. After the year 2000, more than 1,000 km (620 mi) of roads in Sweden have been converted from wide ordinary roads into 2+1-road, all with barriers.

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Wikipedia