Single carriageway

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Single Carriageway
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Birmingham's A38(M) is an example of a multi-lane single carriageway road
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A Single carriageway road is a road where there is a single continuous surface to the road, with no physical barrier separating the directions of travel. It is the most common form of road standard in the United Kingdom and Ireland. The term does not refer to the number of lanes - whilst most single carriageway roads have one lane per direction of traffic (known as S2), two lanes per direction of traffic (known as S4) can be found in many locations. Up until the early 1980s, it was common to find three-lane single carriageway roads (known as S3), where the central lane was designed for use by traffic wishing to overtake slower vehicles but these roads (colloqually known as suicide lanes for obvious reasons) are now very rare - probably the best example is on the A6 near Shap, Westmorland.

The widest single carriageway road in the United Kingdom is the A38(M) Aston Expressway in Birmingham, which is 7 lanes wide and uses Tidal Flow.

Single carriageway roads are generally found on routes with low to medium volumes of traffic.

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Single carriageway
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