Central reservation
Encyclopedia
On divided roads, such as divided highways or freeways/motorway
s, the central reservation (British English
), median, parkway (North American English
), median strip (North American English, New Zealand, and Australian English
) or central nature strip (Australian English) is the area which separates opposing lane
s of traffic
. It may contain landscaping
, planted tree
s, a median barrier, or be simply paved.
s to beautify road
ways. Jurisdiction
s can: plant lawn grasses
with regular mow
ing; hydroseed or scatter wildflower
seed
s to germinate, bloom, and re-seed themselves annually; or create extensive landscape plantings of tree
s, shrub
s, herbaceous perennials
and ornamental grass
es. Where space is at a premium, dense hedge
s of shrubs filter the headlights of oncoming traffic and provide a resilient barrier.
In contrast to the central reservation of a major road, those in urban areas often take the form of central traffic island
s that rise above the roadway. These are frequently found on urban arterial road
s. 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 central reservations 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 reserved central section of the paved roadway, indicated by a space between two sets of double-yellow lines. Similar to an island median, vehicles are only permitted to cross at designated locations. 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.
On British motorways the central reservation is never broken (except on the tidal flow of Aston Expressway), but there are no such restrictions on other dual carriageways. The medians of United States Interstate Highways break only for emergency service lanes, again with no such restrictions on lower classification roads.
The central reservation in the United Kingdom
and other densely populated European countries 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. Two examples of this on the UK road network are on a section of the M6
between Shap and Tebay, where the carriageways are several hundred yards apart, which allows a local road to run between them, and on the M62
where the highest section through the Pennines
famously splits wide enough for a farm in the central reservation. 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).
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 barrier
s in the central reserve. All existing motorways will introduce concrete barriers into the central reserve 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 central reserve 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 5km apart from each other), but converge to a lane's width in suburb
an areas and cities. In urban areas, concrete barriers (such as Jersey barrier
s) and guard rail
s (or guide rail
s) are used.
One median of note is the inverted median of the Golden State Freeway (I-5
) in the Tehachapi Mountains
between Los Angeles, California
and the San Joaquin Valley
. For several miles, the median is inverted—northbound traffic is on the western roadway and southbound traffic on the eastern road. A similar example exists in western Montreal
, on the Autoroute 20
, between the Route 138
and the Turcot Interchange
, where the two directions, on opposite sides of a railway, are reversed (and one enters or exits via the left side). Similarly, I-85
, in central North Carolina, features an inverted median so that an in-median, right-exit rest area can feature a historic bridge.
An August 1993 study by the U.S. 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) in order to have any effect on safety, and that safety benefits of medians increase to a width of 60 to 80 ft (18.3 to 24.4 m). 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.
Controlled-access highway
A controlled-access highway is a highway designed exclusively for high-speed vehicular traffic, with all traffic flow and ingress/egress regulated...
s, the central reservation (British English
British English
British English, or English , is the broad term used to distinguish the forms of the English language used in the United Kingdom from forms used elsewhere...
), median, parkway (North American English
North American English
North American English is the variety of the English language of North America, including that of the United States and Canada. Because of their shared histories and the similarities between the pronunciation, vocabulary and accent of American English and Canadian English, the two spoken languages...
), median strip (North American English, New Zealand, and Australian English
Australian English
Australian English is the name given to the group of dialects spoken in Australia that form a major variety of the English language....
) or central nature strip (Australian English) is the area which separates opposing lane
Lane
A lane is a part of the roadway within a road marked out for use by a single line of vehicles in such a way as to control and guide drivers for the purpose of reducing traffic conflicts. Most public roads have at least two lanes, one for traffic in each direction, separated by Lane markings...
s of traffic
Traffic
Traffic on roads may consist of pedestrians, ridden or herded animals, vehicles, streetcars and other conveyances, either singly or together, while using the public way for purposes of travel...
. It may contain landscaping
Landscape design
Landscape design is an independent profession and a design and art tradition, practised by landscape designers, combining nature and culture. In contemporary practice landscape design bridges between landscape architecture and garden design.-Design scope:...
, planted tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s, a median barrier, or be simply paved.
Physical attributes
Some central reservations function secondarily as green areas and green beltGreen belt
A green belt or greenbelt is a policy and land use designation used in land use planning to retain areas of largely undeveloped, wild, or agricultural land surrounding or neighbouring urban areas. Similar concepts are greenways or green wedges which have a linear character and may run through an...
s to beautify road
Road
A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...
ways. Jurisdiction
Jurisdiction
Jurisdiction is the practical authority granted to a formally constituted legal body or to a political leader to deal with and make pronouncements on legal matters and, by implication, to administer justice within a defined area of responsibility...
s can: plant lawn grasses
Lawn
A lawn is an area of aesthetic and recreational land planted with grasses or other durable plants, which usually are maintained at a low and consistent height. Low ornamental meadows in natural landscaping styles are a contemporary option of a lawn...
with regular mow
Lawn mower
A lawn mower is a machine that uses a revolving blade or blades to cut a lawn at an even length.Lawn mowers employing a blade that rotates about a vertical axis are known as rotary mowers, while those employing a blade assembly that rotates about a horizontal axis are known as cylinder or reel...
ing; hydroseed or scatter wildflower
Wildflower
A wildflower is a flower that grows wild, meaning it was not intentionally seeded or planted. Yet "wildflower" meadows of a few mixed species are sold in seed packets. The term "wildflower" has been made vague by commercial seedsmen who are interested in selling more flowers or seeds more...
seed
Seed
A seed is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and angiosperm plants which occurs after fertilization and some growth within the mother plant...
s to germinate, bloom, and re-seed themselves annually; or create extensive landscape plantings of tree
Tree
A tree is a perennial woody plant. It is most often defined as a woody plant that has many secondary branches supported clear of the ground on a single main stem or trunk with clear apical dominance. A minimum height specification at maturity is cited by some authors, varying from 3 m to...
s, shrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
s, herbaceous perennials
Perennial plant
A perennial plant or simply perennial is a plant that lives for more than two years. The term is often used to differentiate a plant from shorter lived annuals and biennials. The term is sometimes misused by commercial gardeners or horticulturalists to describe only herbaceous perennials...
and ornamental grass
Ornamental grass
Ornamental grasses are grasses grown as ornamental plants. They have become increasingly popular in gardens in recent years.-Classifications:...
es. Where space is at a premium, dense hedge
Hedge (gardening)
A hedge or hedgerow is a line of closely spaced shrubs and tree species, planted and trained in such a way as to form a barrier or to mark the boundary of an area. Hedges used to separate a road from adjoining fields or one field from another, and of sufficient age to incorporate larger trees, are...
s of shrubs filter the headlights of oncoming traffic and provide a resilient barrier.
Traffic island
A traffic island is a solid or painted object in a road that channelises traffic. It can also be a narrow strip of island between roads that intersect at an acute angle. If the island uses road markings only, without raised kerbs or other physical obstructions, it is called a painted island...
s that rise above the roadway. These are frequently found on urban arterial road
Arterial road
An arterial road, or arterial thoroughfare, is a high-capacity urban road. The primary function of an arterial road is to deliver traffic from collector roads to freeways, and between urban centres at the highest level of service possible. As such, many arteries are limited-access roads, or feature...
s. 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 central reservations 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
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, highway medians are sometimes no more than a reserved central section of the paved roadway, indicated by a space between two sets of double-yellow lines. Similar to an island median, vehicles are only permitted to cross at designated locations. 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.
On British motorways the central reservation is never broken (except on the tidal flow of Aston Expressway), but there are no such restrictions on other dual carriageways. The medians of United States Interstate Highways break only for emergency service lanes, again with no such restrictions on lower classification roads.
Width
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and other densely populated European countries 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. Two examples of this on the UK road network are on a section of the M6
M6 motorway
The M6 motorway runs from junction 19 of the M1 at the Catthorpe Interchange, near Rugby via Birmingham then heads north, passing Stoke-on-Trent, Manchester, Preston, Carlisle and terminating at the Gretna junction . Here, just short of the Scottish border it becomes the A74 which continues to...
between Shap and Tebay, where the carriageways are several hundred yards apart, which allows a local road to run between them, and on the M62
M62 motorway
The M62 motorway is a west–east trans-Pennine motorway in Northern England, connecting the cities of Liverpool and Hull via Manchester and Leeds. The road also forms part of the unsigned Euroroutes E20 and E22...
where the highest section through the Pennines
Pennines
The Pennines are a low-rising mountain range, separating the North West of England from Yorkshire and the North East.Often described as the "backbone of England", they form a more-or-less continuous range stretching from the Peak District in Derbyshire, around the northern and eastern edges of...
famously splits wide enough for a farm in the central reservation. The other major exception is the A38(M) Aston Expressway
A38(M) motorway
The A38, also known as the Aston Expressway, is a motorway in Birmingham, England. It is long and was opened on 24 May 1972. It forms part of the much longer A38 route....
, which is a single carriageway of seven lanes, where the median lane moves to account for traffic flow (a system known as tidal flow).
With effect from January 2005 and based primarily on safety grounds, the UK’s Highways Agency
Highways Agency
The Highways Agency is an executive agency, part of the Department for Transport in England. It has responsibility for managing the core road network in England...
's policy is that all new motorway schemes are to use high containment concrete step barrier
Concrete step barrier
A concrete step barrier is a safety barrier used on the central reservation of motorways and dual carriageways as an alternative to the standard steel crash barrier.The barrier has contained all vehicles up to 13.5 tonnes.-United Kingdom:...
s in the central reserve. All existing motorways will introduce concrete barriers into the central reserve 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 central reserve of high speed roads and not to verge side barriers. Other routes will continue to use steel barriers.
In North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
, 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
Trans-Canada Highway
The Trans-Canada Highway is a federal-provincial highway system that joins the ten provinces of Canada. It is, along with the Trans-Siberian Highway and Australia's Highway 1, one of the world's longest national highways, with the main route spanning 8,030 km...
near Ernfold
Ernfold, Saskatchewan
- See also :* List of communities in Saskatchewan* Villages of Saskatchewan-External links:*******-Footnotes:...
, Saskatchewan
Saskatchewan
Saskatchewan is a prairie province in Canada, which has an area of . Saskatchewan is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, and on the south by the U.S. states of Montana and North Dakota....
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, where eastbound and westbound lanes go as far as 5km apart from each other), but converge to a lane's width in suburb
Suburb
The word suburb mostly refers to a residential area, either existing as part of a city or as a separate residential community within commuting distance of a city . Some suburbs have a degree of administrative autonomy, and most have lower population density than inner city neighborhoods...
an areas and cities. In urban areas, concrete barriers (such as Jersey barrier
Jersey barrier
A Jersey barrier or Jersey wall is a modular concrete barrier employed to separate lanes of traffic. It is designed to both minimize vehicle damage in cases of incidental contact while still preventing crossover in the case of head-on accidents....
s) and guard rail
Guard rail
Guard rail or guardrail, sometimes referred to as guide rail or railing, is a system designed to keep people or vehicles from straying into dangerous or off-limits areas...
s (or guide rail
Guide rail
A Guide Rail is a system designed to guide vehicles back to the roadway and away from potentially hazardous situations. There is a legal distinction between a Guide rail and a Guard rail.- Guide Rail Types :...
s) are used.
Interstate 5
Interstate 5 is the main Interstate Highway on the West Coast of the United States, running largely parallel to the Pacific Ocean coastline from Canada to Mexico . It serves some of the largest cities on the U.S...
) in the Tehachapi Mountains
Tehachapi Mountains
The Tehachapi Mountains , regionally also called The Tehachapis, are a mountain range in the Transverse Ranges system of California in the Western United States...
between Los Angeles, California
Los Angeles, California
Los Angeles , with a population at the 2010 United States Census of 3,792,621, is the most populous city in California, USA and the second most populous in the United States, after New York City. It has an area of , and is located in Southern California...
and the San Joaquin Valley
San Joaquin Valley
The San Joaquin Valley is the area of the Central Valley of California that lies south of the Sacramento – San Joaquin River Delta in Stockton...
. For several miles, the median is inverted—northbound traffic is on the western roadway and southbound traffic on the eastern road. A similar example exists in western Montreal
Montreal
Montreal is a city in Canada. It is the largest city in the province of Quebec, the second-largest city in Canada and the seventh largest in North America...
, on the Autoroute 20
Quebec Autoroute 20
Autoroute 20 is a major Quebec Autoroute, following the Saint Lawrence River through one of the more densely-populated parts of Canada, and is part of the Trans-Canada Highway. At , it is the longest Autoroute in Quebec...
, between the Route 138
Quebec route 138
Route 138 is a major highway in the Canadian province of Quebec, following the entire north shore of the Saint Lawrence River past Montreal to the eastern terminus in Natashquan on the Gulf of Saint Lawrence. The western terminus is in Elgin, at the border with New York State south-west of Montreal...
and the Turcot Interchange
Turcot Interchange
The Turcot Interchange is a freeway interchange within the city of Montreal, Quebec, Canada, that links Autoroutes 15, 20, and 720. It takes its name from the currently-abandoned Turcot rail yards over which it is built....
, where the two directions, on opposite sides of a railway, are reversed (and one enters or exits via the left side). Similarly, I-85
Interstate 85
Interstate 85 is a major interstate highway in the Southeastern United States. Its current southern terminus is at an interchange with Interstate 65 in Montgomery, Alabama; its northern terminus interchanges with Interstate 95 in Petersburg, Virginia, near Richmond...
, in central North Carolina, features an inverted median so that an in-median, right-exit rest area can feature a historic bridge.
Safety
Federal Highway Administration
The Federal Highway Administration is a division of the United States Department of Transportation that specializes in highway transportation. The agency's major activities are grouped into two "programs," the Federal-aid Highway Program and the Federal Lands Highway Program...
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) in order to have any effect on safety, and that safety benefits of medians increase to a width of 60 to 80 ft (18.3 to 24.4 m). 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.