Single-track road

A single-track road or one-lane road is a road that permits two-way travel but is not wide enough in most places to allow vehicles to pass one another (although sometimes two compact cars can pass). This kind of road is common in rural areas across the United Kingdom and elsewhere. To accommodate two-way traffic, many single-track roads, especially those officially designated as such, are provided with passing places (United Kingdom) or pullouts or turnouts (United States), or simply wide spots in the road, which may be scarcely longer than a typical automobile using the road. The distance between passing places varies considerably, depending on the terrain and the volume of traffic on the road. The railway analog for passing places are passing loops.

The term is widely used in Scotland, particularly the Highlands, to describe such roads. Passing places are generally marked with a diamond-shaped white sign with the words "passing place" on it. New signs tend to be square rather than diamond-shaped, as diamond signs are also used for instructions to tram drivers in cities. On some roads, especially in Argyll and Bute, passing places are marked with black-and-white-striped posts. Signs remind drivers of slower vehicles to pull over into a passing place (or opposite it, if it is on the opposite side of the road) to let following vehicles pass, and most drivers oblige. The same system is found very occasionally in rural England and Wales. Sometimes two small vehicles can pass one another at a place other than a designated passing place.

Some A-class and B-class roads in the Highlands are still single-track, although many sections have been widened for the sake of faster travel. In 2009, the A830 "Road to the Isles" and A851 on Skye have had their single-track sections replaced with higher-quality single-carriageway road.

...
Wikipedia