Shoulder (road)

Shoulders have multiple uses, including:

• Emergency vehicles such as ambulances, fire trucks and police cars may use the shoulder to bypass traffic congestion in some countries.
• In the event of an emergency or breakdown, a motorist can pull into the shoulder to get out of the flow of traffic and obtain a greater degree of safety.
• Active traffic management, used on busy multi-lane roads, may allow 'hard shoulder running' by general traffic at reduced speeds during periods of high traffic volumes.
• In some places a "bus bypass shoulder" may be provided which allows bus services to pass stationary traffic.
• Paved shoulders provide additional space should a motorist need to take evasive action (such as avoiding a wrong-way driver) or need to recover control of their vehicle before a run-off-road collision occurs.
• In some rural areas without sidewalks, pedestrians and cyclists may be allowed to walk or ride on the shoulders.
• On curbed roadways, shoulders move the gutter away from the travel lanes which reduces the risk of hydroplaning, and reduces splash and spray of stormwater onto pedestrians using any adjacent sidewalk.
• Paved shoulders move water away from the roadway before it can infiltrate into the road's subbase, increasing the life expectancy of the road surface.
• Shoulders help provide extra structural support of the roadway.
• When semi-truck drivers need sleep and there are no available parking spaces at truck stops and rest areas, either because there are no such facilities nearby or because all semi-truck parking spaces are filled to capacity, drivers may pull over to the highway shoulder and sleep in their truck cabin.
• In some countries, parking in the shoulder is not prohibited by the law, and mushroom and berry pickers commonly use them on roads going through a forest.

In Ireland, dashed yellow lines demarcate hard shoulders on non-motorways, as can be seen along this dual carriageway on the N11.

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 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 maneuvers. 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.[2]

The US Federal Highway Administration encourages the placement of a Safety Edge—a 30° compacted taper on the end of the pavement dropoff—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 nonexistent.[3]

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 center 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 northeastern 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 12 feet (3.7 m). 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.

The Dulles Airport Express bypassing traffic using the shoulder lane

In some jurisdictions in the United States and Canada, buses are allowed to drive on the shoulder to pass traffic jams, which is called a bus-only shoulder or bus-bypass shoulder (BBS);[4] the term "bus-only shoulder lane" is incorrect from a technical and legal standpoint.[5] In Ontario, Highway 403 had its shoulders between Hurontario Street and Erin Mills Parkway widened in 2003 so they serve a dual purpose as bus lanes and accident lanes. In the Minneapolis–Saint Paul region of Minnesota, over 270 miles of shoulder have been designated for use by buses.[6] The Route 9 BBS in Central New Jersey which runs along two stretches of shoulders are dedicated for exclusive bus use during peak hours.[7][8] The bus lanes, which run for approximately 3 miles (4.83 km) are the first component of a planned 20-mile (32.19 km) BBS corridor.[9] In the Chicago area, Pace buses are authorized to use the shoulder of the Jane Addams Memorial Tollway, Edens Expressway, and Stevenson Expressway to avoid traffic congestion.[10]

In the Seattle area, Community Transit and Sound Transit Express commuter buses are authorized to use the shoulders of Interstate 5 and Interstate 405 on small segments in Snohomish County as part of a pilot project that aims to reduce delayed bus trips.[11]

There are also some bus-bypass shoulders in the United Kingdom, on the motorways of Northern Ireland heading towards Belfast and the M90 motorway in Scotland towards Edinburgh.

Sign-controlled peak shoulder lane on Interstate 405 near Seattle, Washington, U.S.

The M42, with lowered speed limits and hard-shoulder running, as seen on the matrix Variable Message Sign (VMS) on the left.

In the United Kingdom, usage of the hard shoulder is known as "hard shoulder running". A pilot project on an 11-mile stretch of the M42 motorway, near Birmingham, began in September 2006. Active traffic management with special signage, new turnouts (laybys) and a variable speed limit have been put in place to improve safety. This has proved very successful, with journey times decreasing by 26% northbound and 9% southbound. Drivers can also better predict their journey times as the variability decreased by 27%. The average accident rate dropped from 5.2 to 1.5 per month.[12] It has also proved popular with motorists, 60% of whom want to see it expanded to other English motorways. This 'smart motorway' system has been expanded to the M6,[13] M1[14] and M25,[15] as well as parts of the M60 and M62.[16]

In the United States, on Interstate 93 between Exit 35 (formerly 41)[17] and Exit 43 (formerly 46)[18] and SR 3 between Exit 27 (formerly 12)[19] and Exit 38 (formerly 16)[20] in the Boston metro area, cars are allowed to use the shoulder as they would a normal lane during morning and evening rush hours. The same scheme is employed elsewhere, such as on Interstate 580 in California on the Richmond-San Rafael Bridge, on Interstate 66 in Virginia between the Capital Beltway and US-50, and on Interstate 405 between SR 527 and I-5 in Bothell.[21]

Florida has developed a plan for the use of shoulders by moving traffic during hurricane evacuations on select portions of Interstate 4, Interstate 10, Interstate 75, and Interstate 95.[22][23] The shoulder-use plan was implemented in place of labor- and resource-intensive contraflow lane reversal, in which both sides of an interstate highway are used for one direction of traffic.[23] The first implementation of the plan occurred on 8–9 September 2017 before the arrival of Hurricane Irma.[24][25][26] Texas has also considered emergency shoulder use for hurricane evacuations.[23]

Although direct rear impacts only make up 3% of motorist-on-cyclist collisions, they are a more prominent collision type in arterial road type situations. When they occur in such circumstances, they are also associated with significantly increased risk of fatality. Data collated by the OECD indicates that rural locations account for 35% or more of cycling fatalities in Denmark, Finland, France, Great Britain, Japan, the Netherlands, and Spain.[27]

The use of appropriately designed segregated space on arterial or interurban routes appears to be associated with reductions in overall risk. In Ireland, the provision of hard shoulders on interurban routes in the 1970s reportedly resulted in a 50% decrease in accidents.[28] It is reported that the Danes have also found that separate cycle tracks lead to a reduction in rural collisions.[29]

In some countries, the use of shoulders is optional for cyclists, who may choose not to use it for reasons such as: it being too narrow, inviting dangerously close passes at high speed by motorists; it having a road surface unsuitable for cycling or putting the path of the cyclist in direct conflict with the paths of other road users, such as those turning across the shoulder. Generally, the usable width of the road begins where one can ride without increased danger of falls, jolts or blowouts. A road may have a gravel shoulder, its edge may be covered with sand or trash and the pavement may be broken.[30]

• Bus lane
• Road verge
• Rumble strip
• Wide outside lane

• Traffic Signs about Shoulders
• Deaths in Emergency Lanes - National Coroners Information System (NCIS) Fact-Sheet, January 2011