Median strip

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Typical left-hand motorway road layout in Ireland and South Africa. Ireland Road Lanes.svg
Typical left-hand motorway road layout in Ireland and South Africa.
Divided median strip on a highway in Huizhou Divided median strip on a highway in Huizhou.jpg
Divided median strip on a highway in Huizhou

The median strip, central reservation, roadway median, or traffic median is the reserved area that separates opposing lanes of traffic on divided roadways such as divided highways, dual carriageways, freeways, and motorways. The term also applies to divided roadways other than highways, including some major streets in urban or suburban areas. The reserved area may simply be paved, but commonly it is adapted to other functions; for example, it may accommodate decorative landscaping, trees, a median barrier, or railway, rapid transit, light rail, or streetcar lines.

Contents

Regional terminology

There is no international English standard for the term. Median, median strip, and median divider island are common in North American and Antipodean English. Variants in North American English include regional terms such as neutral ground in New Orleans usage.

In British English the central reservation or central median is the preferred usage; it also occurs widely in formal documents in some non-British regions such as South Africa, where there are other informal regional words (for example middelmannetjie, which originally referred to the hump between wheel ruts on a dust road). [1] [2] Neutral section and central nature strip[ citation needed ] are coinages in Australian English.

Additionally, different terminology is used to identify traffic lanes in a multi-lane roadway. North American usage calls the leftmost lanes located closest to the roadway centerline the "inner" lanes, while British usage calls these lanes the "outer" lanes. Thus, it is less confusing to call these central lanes the "passing", "fast", or "overtaking" lanes in international contexts, instead of using the ambiguous inner/outer distinction. Regional differences between right-hand traffic and left-hand traffic can cause further confusion.

Physical attributes

A grass median strip on Interstate 80 in Pennsylvania, United States Interstate 80 in Hemlock Township, Columbia County, Pennsylvania.JPG
A grass median strip on Interstate 80 in Pennsylvania, United States

Some medians function secondarily as green areas and green belts to beautify roadways. Jurisdictions can: plant lawn grasses with regular mowing; hydroseed or scatter wildflower seeds to germinate, bloom, and re-seed themselves annually; or create extensive landscape plantings of trees, shrubs, herbaceous perennials and ornamental grasses. Where space is at a premium, dense hedges of shrubs filter the headlights of oncoming traffic and provide a resilient barrier. In other areas, the median may be occupied by a right-of-way for a public transportation system such as a light rail or rapid transit line; for example, the Red and Blue Lines of the Chicago 'L' partially run in the medians of the Dan Ryan, Eisenhower, and Kennedy Expressways. [3]

A California arterial road median with decorative cobblestones inset Rockmedian.jpg
A California arterial road median with decorative cobblestones inset

In contrast to the median of a major road, those in urban areas often take the form of central traffic islands that rise above the roadway. These are frequently found on urban arterial roads. In their simplest form, these are just raised concrete curbs, but can also be landscaped with grass or trees or decorated with bricks or stones. Such medians are also sometimes found on more minor or residential streets, where they serve primarily as a traffic-calming or landscaping element rather than a safety enhancement to restrict turns and separate opposite directions of high-volume traffic flow.

In some areas such as California, highway medians are sometimes no more than a demarcated section of the paved roadway, indicated by a space between two sets of double yellow lines. Such a double-double yellow line or painted median is legally similar to an island median: vehicles are not permitted to cross it, unlike a single set of double yellow lines which may in some cases permit turns across the line. [4] This arrangement has been used to reduce costs, including narrower medians than are feasible with a planted strip, but research indicates that such narrow medians may have minimal safety benefit compared to no median at all. [5]

The medians of United States Interstate Highways break only for emergency service lanes, with no such restrictions on lower classification roads. On British motorways, the median is never broken (except on the tidal flow of Aston Expressway), but there are no such restrictions on other dual carriageways.

Width

The wide median strip in Main Street, Bairnsdale, Victoria, Australia has been made into a garden feature of the town, wide enough to accommodate features such as flowerbeds and street furniture like benches and postboxes. From-Rotunda-Looking-West-Bairnsdale-Vic.jpg
The wide median strip in Main Street, Bairnsdale, Victoria, Australia has been made into a garden feature of the town, wide enough to accommodate features such as flowerbeds and street furniture like benches and postboxes.

The central reservation in the United Kingdom and other densely populated European countries (where it is known by their local names) is usually no wider than a single lane of traffic. In some cases, however, it is extended. For instance, if the road is running through hilly terrain, the carriageways may have to be built on different levels of the slope. An example of this is on the M5 motorway as it climbs up the side of the Gordano Valley south of Bristol. In Birmingham and many other cities, suburban dual carriageways may have trees or cycle lanes in the middle as a wide central reservation.

Two examples on the UK road network where the carriageways are several hundred yards/metres apart, are on a section of the M6 between Shap and Tebay, which allows a local road to run between them, and on the M62 where the highest section through the Pennines famously splits wide enough to contain a farm. [6] The other major exception is the A38(M) Aston Expressway, which is a single carriageway of seven lanes, where the median lane moves to account for traffic flow (a system known as tidal flow or reversible lane).

With effect from January 2005 and based primarily on safety grounds, the UK's Highways Agency's policy is that all new motorway schemes are to use high containment concrete step barriers in the median (central reservation). All existing motorways will introduce concrete barriers as part of ongoing upgrades and through replacement as and when the current systems have reached the end of their useful life. This change of policy applies only to barriers in the median of high speed roads and not to verge side barriers. Other routes will continue to use steel barriers.

In North America, and some other countries with large sparsely populated areas, opposing lanes of traffic may be separated by several hundred meters of fields or forests outside of heavily populated areas (an extreme example being the Trans-Canada Highway near Ernfold, Saskatchewan, Canada, where eastbound and westbound lanes go as far as 5 kilometres (3.1 mi) apart from each other), but converge to a lane's width of separation in suburban areas and cities. In urban areas, concrete barriers (such as Jersey barriers) and guard rails (or guide rails) are used.

In Dedham, Massachusetts, the Norfolk County Correctional Center (a state prison) is located entirely within a wide median of Massachusetts Route 128. This 502-bed facility was opened in 1993 as infill construction in the previously unused real estate that had been isolated by the divided highway in the early 1950s. An extreme example of a wide median can be found on Interstate 75 near Cincinnati, Ohio; nearly the entire village of Arlington Heights, as well as the downtown district of Lockland, are both located between the two directions of I-75.

A 50-metre-wide median strip in Inagi, Tokyo. Onekankoyodai.JPG
A 50-metre-wide median strip in Inagi, Tokyo.

Inverted median

Some freeways in North America include "inverted" medians, which separate roadways running in the opposite direction from the standard for the country they are located in. Roads are so designed for a number of reasons, including to save space or for the creation of continuous flow intersections.

Inverted medians are also used in rare cases on local streets that historically had unusual traffic patterns, such as Bainbridge Street between 3rd Street and 5th Street in Philadelphia.

Safety impact

Concrete median barrier on the N11 road near Dublin, Ireland N11 dual-carriageway median barrier.jpg
Concrete median barrier on the N11 road near Dublin, Ireland

An August 1993 study by the US Federal Highway Administration quantified the correlation between median width and the reduction of both head-on accidents and severe injuries. The study found that medians without barriers should be constructed more than 30 feet (9.1 m) wide in order to have any effect on safety, and that safety benefits of wider medians continue to increase to a width of 60 to 80 feet (18.3 to 24.4 m). [5]

A consequence of this finding is that decreasing the size of a median to 20 feet (6.1 m) from 30 feet (9.1 m) to add lanes to a highway may result in a less safe highway. Statistics regarding medians with barriers were not calculated in this study. [5]

Bus rapid transit

Central reservations may also be used for reserved bus lanes, as in Istanbul's Metrobus, Los Angeles's J Line and Bogotá's TransMilenio. Center-lane running and island platforms installed in the medium reduce conflicts with stopped and parked cars as well as pedestrians near the curb, thus speeding service.

Railway use

In some cases, the median strip of the highway may contain a train line, usually around major urban centers. This is often done to share a right-of-way, because of the expense and difficulty of clearing a route through dense urban neighborhoods. A reserved right-of-way is contrasted with street running, in which rail cars and automobiles occupy the same lanes of traffic.

Train lines that run in the median of highways include:

Asia

Europe

North America

Canada

United States

California

Oceania

South America


City planners also commonly use median strips to accommodate urban tram tracks along a central segregated track, and examples of this layout are found across Europe. Some of the earliest practices of incorporating central tramways into road designs were pioneered in Liverpool by John Alexander Brodie, and later emulated in Manchester, such as along Princess Parkway or Kingsway. [8]

See also

Related Research Articles

<span class="mw-page-title-main">Highway</span> Public road or other public way on land

A highway is any public or private road or other public way on land. It is used for major roads, but also includes other public roads and public tracks. In the United States, it is used as an equivalent term to controlled-access highway, or a translation for Autobahn, autoroute, etc.

<span class="mw-page-title-main">Interstate 45</span> Interstate Highway in Texas

Interstate 45 (I-45) is a major Interstate Highway located entirely within the U.S. state of Texas. While most Interstate routes which have numbers ending in "5" are cross-country north–south routes, I-45 is comparatively short, with the entire route located in Texas. Additionally, it has the shortest length of all the interstates that end in a "5". It connects the cities of Dallas and Houston, continuing southeast from Houston to Galveston over the Galveston Causeway to the Gulf of Mexico.

The Frederick G. Gardiner Expressway, commonly known as the Gardiner Expressway or simply the Gardiner, is a partially at grade and elevated municipal expressway in Toronto, Ontario, Canada. Running close to the shore of Lake Ontario, it extends from the foot of the Don Valley Parkway (DVP) in the east, just past the mouth of the Don River, to the junction of Highway 427 and the Queen Elizabeth Way (QEW) in the west, for a total length of 18.0 kilometres (11.2 mi). East of Dufferin Street to just east of the Don River, the roadway is elevated for a length of 6.8 kilometres (4.2 mi), unofficially making it the longest bridge in Ontario. It runs above Lake Shore Boulevard east of Spadina Avenue. The Gardiner Expressway is wholly owned and operated by the City of Toronto.

<span class="mw-page-title-main">Frontage road</span> Type of road

A frontage road is a local road running parallel to a higher-speed, limited-access road. A frontage road is often used to provide access to private driveways, shops, houses, industries or farms. Where parallel high-speed roads are provided as part of a major highway, these are also known as local lanes. Sometimes a similar arrangement is used for city roads; for example, the collector portion of Commonwealth Avenue in Boston, Massachusetts, is known as a carriage road.

<span class="mw-page-title-main">Shoulder (road)</span> Reserve lane by the verge of a roadway

A shoulder, hard shoulder (British) or breakdown lane 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.

<span class="mw-page-title-main">Dual carriageway</span> Type of road

A dual carriageway (BrE) or a divided highway (AmE) is a class of highway with carriageways for traffic travelling in opposite directions separated by a central reservation (BrE) or median (AmE). Roads with two or more carriageways which are designed to higher standards with controlled access are generally classed as motorways, freeways, etc., rather than dual carriageways.

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<span class="mw-page-title-main">Interstate 695 (Maryland)</span> Highway in Maryland

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<span class="mw-page-title-main">Reversible lane</span> Lane in which traffic may travel in either direction

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<span class="mw-page-title-main">Limited-access road</span> High-speed road with many characteristics of a controlled-access highway (freeway or motorway)

A limited-access road, known by various terms worldwide, including limited-access highway, dual-carriageway, expressway, and partial controlled-access highway, is a highway or arterial road for high-speed traffic which has many or most characteristics of a controlled-access highway, including limited or no access to adjacent property, some degree of separation of opposing traffic flow, use of grade separated interchanges to some extent, prohibition of slow modes of transport, such as bicycles, horse-drawn vehicles or ridden horses, or self-propelled agricultural machines; and very few or no intersecting cross-streets or level crossings. The degree of isolation from local traffic allowed varies between countries and regions. The precise definition of these terms varies by jurisdiction.

<span class="mw-page-title-main">Interstate 264 (Virginia)</span> Interstate Highway in southeastern Virginia, US

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<span class="mw-page-title-main">Controlled-access highway</span> Highway designed for high-speed, regulated traffic flow

A controlled-access highway is a type of highway that has been designed for high-speed vehicular traffic, with all traffic flow—ingress and egress—regulated. Common English terms are freeway, motorway and expressway. Other similar terms include throughway and parkway. Some of these may be limited-access highways, although this term can also refer to a class of highways with somewhat less isolation from other traffic.

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This article describes the highway systems available in selected countries.

<span class="mw-page-title-main">Glossary of road transport terms</span>

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References

  1. Branford, Jean & Branford, William. A Dictionary of South African English. Oxford University Press 1992 ISBN   978-0195705959
  2. Bosman, D. B.; Van der Merwe, I. W.; Hiemstra, L. W. (1984). Tweetalige Woordeboek Afrikaans-Engels. Tafelberg-uitgewers. ISBN   978-0-624-00533-9.
  3. Buck, Thomas (September 28, 1969). "Ryan Rail Service Starts Today". Chicago Daily Tribune. p. 22.
  4. "Crossing double yellow lines", Spokesman-Review , April 28, 2014.
  5. 1 2 3 Federal Highway Administration (August 1993). "The Association Of Median Width And Highway Accident Rate" . Retrieved 2008-01-09.
  6. Google Maps
  7. Ortofoto (Map). Lantmäteriet . Retrieved 17 August 2018.
  8. Crosby, Alan, ed. (1998). Leading the way : a history of Lancashire's roads. Preston: Lancashire County Books. p. 212. ISBN   9781871236330.