|The A465 near Gilwern, an example of an S2+1 road|
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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.