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A465 Gilwern - Coppermine - 12701.jpg
The A465 near Gilwern, an example of an S2+1 road
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S2+1 roads refer to a specific class of single carriageway roads which have two lanes in one direction and only one lane in the opposing direction. The opposing flows are not separated from each other by anything more than painted lines.

Some S2+1 roads allow overtaking from the one lane section into the two lane section, others have double white lines meaning overtaking from the one lane section is not permitted.

They are most often found in long distance single carriageway roads where an up hill crawler lane is required, or to give overtaking opportunities where sometimes 'alternating S2+1' is used.

In Ireland, the 1998 Road Needs Study concluded: "this type of road would not give any additional capacity compared with the wide 2 lane road typically used, has a poor safety record and is generally incompatible with the frequency of junctions and roadside developments in Irish conditions". It observed that Scotland had some success with the layout, while the Netherlands was trialling S2+1 with a central barrier.

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