Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. 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 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 Carriageways. 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.

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