A shoulder, often serving as an emergency stopping lane, is a reserved lane by the verge of a road or motorway, on the right in countries which drive on the right, or on the left side in Japan, the UK, Australia, and other left-side driving countries. Many wider U.S. as well as Swedish freeways 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 (see below).
Shoulders have multiple uses, including:
- 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.
- Emergency vehicles such as ambulances and police cars may use the shoulder to bypass traffic congestion.
- 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 urban areas, shoulders are used as travel lanes during peak commuting hours.
- 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.
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.
The U.S. 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 pavement. The Safety Edge is effective on roads where the shoulder is narrow nor nonexistent.
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 collects 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, as well as 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 meters wide, which is not wide enough for some automobiles. (A standard lane in the US and UK is 12 feet or 3.65 meters.) 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 result is often a traffic jam and occasionally a collision.
Bus bypass shoulder
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); the term "bus-only shoulder lane" is incorrect from a technical and legal standpoint.
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-St. Paul region of Minnesota, over 270 miles of shoulder have been designated for use by buses. The Route 9 BBS in Central New Jersey which runs along two stretches of shoulders are dedicated for exclusive bus use during peak hours. 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.
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.
Peak period use by all traffic
On specially signed sections of highway 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 66 in Virginia between the Capital Beltway and US-50.
In the UK, 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. 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. It has also proved popular with motorists, 60% of whom want to see it expanded to other English motorways. The system has been expanded to the M6, M1 and M25, with plans to implement it to parts of M60 and M62 by 2015.
Increased cyclist safety
Although direct rear impacts only make up 3% of motorist-on-cyclist collisions, they are a more prominent collision type in arterial/rural 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.
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. It is reported that the Danes have also found that separate cycle tracks lead to a reduction in rural collisions.
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, as shoulders may not be intended for wheeled vehicles; and it 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.
Characteristics in various countries
Republic of Ireland
Full-width hard shoulders are provided on most new, upgraded (from the 1980s onwards), and major national roads in the Republic of Ireland, especially on wide two-lane and dual-carriageway roads (the shoulders on most 2+1 roads are narrow however). They are defined within the official document the Rules of the Road as a part of the road that should normally only be used by cyclists and pedestrians. Their provision of on interurban routes in the 1970s reportedly resulted in a 50% decrease in accidents involving pedal cyclists.
The hard shoulder is usually demarcated by road markings in the form of a single dashed yellow line with the addition of yellow cat's eyes. On motorways, and at critical points on other routes (e.g. between junctions or interchanges, or beneath overpasses) a solid yellow line is used, denoting additional restrictions on usage of the hard shoulder. At junctions and on-ramps and off-ramps, the yellow line peels away into the turn, with a dashed white line (with green cats' eyes) denoting a lane division following the main route (i.e. in most cases the road remains the same width, and a turn lane takes the place of the hard shoulder).
In the 2000s, Bus Éireann coaches were allowed to use the hard shoulders on national roads into Dublin. However, dedicated bus lanes are now present on sections of some routes, such as the N7 Naas Road, and such use of actual hard shoulder is not universal.
The right-hand shoulder is separated by a solid white line, and the left-hand shoulder (if the road is one-way, such as part of a divided highway) is separated from the leftmost through lane by a solid yellow line. On many roads the lines are supplemented by reflective raised pavement markers or rumble strips placed every few feet in order to provide additional visual and tactile feedback to drivers crossing the lines.
Normally one is not allowed to drive on the shoulder but in the case of traffic block, in some jurisdictions, use of the shoulder may be allowed for the purpose of reaching an exit if the exit is within 200 feet.
On freeways in foggy areas of California, there is an obvious break in the line of the shoulder before every exit; this is to help drivers find their exits in heavy fog (especially dangerous tule fog).
Full width hard shoulders are usually provided only on motorways and are usually 3.3 meters wide, but there are exceptions. Some motorways do not have hard shoulders at all (for example the A57(M)) and there are a small number of dual carriageway A-roads which do possess hard shoulders (for example, parts of the A1, A2 and A27). Hard shoulders are always marked with a reflectorized solid white line which is 20 cm wide and is provided with a rumble strip. A line of red cats' eyes is also used, and is placed to the side of the line. Sometimes, a hard shoulder will be colored differently (usually red) to that of the main carriageway lanes.
On many modern non-motorway roads, a hard strip is provided. These are usually 1 metre wide, and are bounded by thinner solid white lines, and often without a rumble strip.
The shoulder located on the side of Italy's highway is normally used as emergency lane in case of breakdown or is used by emergency vehicles in case of queues. According to the regulation in force it is mandatory wear a high visibility jacket when dismounting from the vehicle stopped on emergency lane.
Normally one is not allowed to drive on the shoulder but in case of traffic block, use of the shoulder is allowed to reach an exit if the exit is within 500 meters.
In a similar manner to Italy and the United States, as described above, the shoulders located on the side of Australia's highways are normally used as an emergency lane in the case of a breakdown or by emergency vehicles in the case of road congestion. However, no mandatory regulations exist to wear a high visibility jacket when dismounting from the vehicle stopped in an emergency lane.
A recent study conducted by the National Coroners Information System (NCIS) in Australia  has revealed twenty-nine (29) closed case fatalities (and at least a dozen case fatalities still under coronial investigation) that had been reported to Australian coroners where a person was "struck in an emergency lane after their vehicle had stopped" between July 2000 and November 2010.
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