Shoulder (road)

A shoulder (American English), hard shoulder (British English) or breakdown lane (Australian English) is an emergency stopping lane by the verge on the outer side of a road or motorway. Many wider freeways, or expressways elsewhere have shoulders on both sides of each directional carriageway—in the median, as well as at the outer edges of the road, for additional safety. Shoulders are not intended for use by through traffic, although there are exceptions.

Shoulders have multiple uses, including:

The shoulder is usually slightly narrower than a full traffic lane. In some cases, particularly on older rural roadways, shoulders that initially existed were hardened with gravel rather than being paved with asphalt, tarmac or concrete. In Britain, motorway shoulders are now paved, but are still known as "hard shoulders". Older, gravel shoulders have sometimes been termed soft shoulders by comparison. Because the paved surface ends at that point, they are less safe if they need to be used for emergency manoeuvres. Notably, the section of Ontario Highway 401 between Windsor and London had soft shoulders with a sharp slope which was blamed for facilitating vehicle rollovers, if drivers accidentally drifted off the paved section of the road and then overreacted after hitting the gravel. Modern practice is to build a continuous paved shoulder whenever possible.

The US Federal Highway Administration encourages the placement of a Safety Edge—a 30° compacted taper on the end of the pavement drop-off—to ensure that any driver running off the edge of the roadway is better able to maintain control while trying to steer back onto the roadway. The Safety Edge is effective on roads where the shoulder is narrow or non-existent.

To save money, the shoulder was often not paved to the same thickness as the through lanes, so if vehicles were to attempt to use it as a through lane regularly, it would rapidly deteriorate. In Britain, shoulder running can occur during roadworks, and full depth construction is now standard. In some metro areas, road authorities also allow shoulders to be used as lanes at peak periods. However, rural shoulders often collect various bits of road debris that can make driving there less safe.

Drivers will sometimes drift into the shoulder when being overtaken by passing vehicles, particularly on two-lane roads. However, it is extremely unsafe, and in most jurisdictions illegal, to abuse the shoulder by 'undertaking' passing vehicles that are nearer the centre of the road.

On older roads, the shoulder may disappear for short periods, near exits or when going across or under bridges or tunnels where the cost savings were thought to outweigh the safety benefits of the shoulder. Some roads have a narrow shoulder for significant distances. This makes it difficult for large vehicles to pull into the hard shoulder altogether.

The Jingjintang Expressway in north-eastern China is an example of this phenomenon. Its shoulder is only 2.4 metres (7.9 ft) wide, which is not wide enough for some automobiles—a standard lane in the U.S. and UK is 3.7 metres (12 ft). As a result, some motorists are unable to fully exit the mainline when they need to pull over, so they end up in a position that is halfway in the rightmost lane and only partly on the shoulder. The end result is often a traffic jam and occasionally a collision.