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A curb (
North American English North American English (NAmE, NAE) is the most generalized variety of the English language as spoken in the United States and Canada. Because of their related histories and cultures, plus the similarities between the pronunciations (accents), v ...
), or kerb (
Commonwealth English The use of the English language in current and former member countries of the Commonwealth of Nations was largely inherited from British colonisation, with some exceptions. English serves as the medium of inter-Commonwealth relations. Many r ...
except
Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...
; see spelling differences), is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway.


History

Although curbs have been used throughout modern history, and indeed were present in ancient Pompeii, their widespread construction and use only began in the 18th century, as a part of the various movements towards city beautification that were attempted in the period. A series of Paving Acts in the 18th century, especially the 1766 Paving and Lighting Act, authorized the
City of London Corporation The City of London Corporation, officially and legally the Mayor and Commonalty and Citizens of the City of London, is the municipal governing body of the City of London, the historic centre of London and the location of much of the United King ...
to create footways along the streets of London, pave them with
Purbeck stone Purbeck stone refers to building stone taken from a series of limestone beds found in the Upper Jurassic to Lower Cretaceous Purbeck Group, found on the Isle of Purbeck, Dorset in southern England. The best known variety of this stone is Purbeck ...
(the thoroughfare in the middle was generally cobblestone) and raise them above street level with curbs forming the separation. The Corporation was also made responsible for the regular upkeep of the roads, including their cleaning and repair, for which they charged a tax from 1766. Previously, small wooden bollards had been put up to demarcate the area of the street reserved for pedestrian use. By the late 18th century, this method of separating pedestrians from carriageways had largely been supplanted by the use of curbs. With the introduction of macadam roads in the early 19th-century, curbs became ubiquitous in the streets of London. Curbs present an obstacle for accessibility to physically disabled persons in public spaces. In 1945, Jack Fisher of Kalamazoo, Michigan, celebrated the installation of one of the nation's first
curb cut A curb cut (U.S.), curb ramp, depressed curb, dropped kerb ( UK), pram ramp, or kerb ramp ( Australia) is a solid (usually concrete) ramp graded down from the top surface of a sidewalk to the surface of an adjoining street. It is designed primaril ...
s to facilitate mobility in the center of the city. In the United States, activism and passage of federal legislation on accessibility requirements such as the
Americans with Disabilities Act of 1990 The Americans with Disabilities Act of 1990 or ADA () is a civil rights law that prohibits discrimination based on disability. It affords similar protections against discrimination to Americans with disabilities as the Civil Rights Act of 1964, ...
(ADA) have facilitated travel for
wheelchair A wheelchair is a chair with wheels, used when walking is difficult or impossible due to illness, injury, problems related to old age, or disability. These can include spinal cord injuries ( paraplegia, hemiplegia, and quadriplegia), cerebr ...
users and other people.


Function

Curbs may fulfill any or several of a number of functions. By delineating the edge of the pavement, they separate the road from the roadside and discourage drivers from parking or driving on sidewalks and lawns. They also provide structural support to the pavement edge. Curbs can be used to channel runoff water from rain or melted snow and ice into storm drains. There is also an aesthetic aspect, in that curbs look formal and "finished". Since curbs add to the cost of a road, they are generally limited to urban and suburban areas and are rarely found in rural areas except where certain drainage conditions (such as mountains or culverts) make them necessary. Curbs are not universally used, however, even in urban settings (see
living street A living street is a street designed with the interests of pedestrians and cyclists in mind by providing enriching and experiential spaces. Living streets also act as social spaces, allowing children to play and encouraging social interactions ...
).


Safety

In low-speed environments, curbs are effective at channeling motor vehicle traffic and can provide some redirective capacity for low-speed impacts. On higher speed roads, the main function of curbs is to provide drainage, and they are mostly used in areas of a bridge approach or other locations with
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is dis ...
risk. A high-speed vehicle that hits a curb may actually turn towards the sidewalk, rather than be directed away from it. A vehicle that strikes a curb can also be tripped into a rollover crash or vaulted into the air. The vehicle could be vaulted over a
traffic barrier Traffic barriers (sometimes called Armco barriers,AK Steel (formerly Armco) genericized trademark also known in North America as guardrails or guard rails and in Britain as crash barriers) keep vehicles within their roadway and prevent them from ...
into the object the barrier is intended to shield. This is a reason why they are rarely used on rural or high-speed roads. Where a curb is used with a traffic barrier, the barrier should either be close to or well behind the curb, to reduce the chances of a vehicle going over the barrier. Depending on the area and the distance between the travel lane and the edge of the pavement, an edge line can be used to indicate the outside (shoulder) edge of the road.
Retroreflective A retroreflector (sometimes called a retroflector or cataphote) is a device or surface that reflects radiation (usually light) back to its source with minimum scattering. This works at a wide range of angle of incidence, unlike a planar mirror, ...
road marking Road surface marking is any kind of device or material that is used on a road surface in order to convey official information; they are commonly placed with road marking machines (also referred to as road marking equipment or pavement marking eq ...
material can also be applied to the curb itself to make it more conspicuous. Curbs are also meant to inform pedestrians to stop or slow down as they prepare to cross roadways. For example, cultural context and behavioral norms of a society may affect safety in that people are more likely to cross on a red light while standing alone than waiting with others at the curb.


Types of curb

There are a number of types of curbs, categorized by shape, material, height, and whether the curb is combined with a
gutter Gutter may refer to: Water discharge structures * Rain gutter, used on roofs and in buildings * Street gutter, for drainage of streets Design and printing * Gutter, in typography, the space between columns of printed text * Gutter, in bookbi ...
. Most curb is constructed separately from the pavement, and the gutter is formed at the joint between the roadway and the curb. The combined curb and gutter (also called "curb and channel") has a concrete curb and gutter cast together in one piece. "Integral curb" is curbing constructed integrally as a part of the concrete pavement.


Shape

Curbs often have a vertical or nearly-vertical face, also called "barrier", "non-mountable", or "insurmountable curb". A vertical-faced curb is used to discourage motor vehicle drivers from leaving the roadway. The square (90°-edge) or close-to-square type is still almost always used in towns and cities, as it is a straight step down and thus less likely to be tripped-over by pedestrians. By contrast, a slope-faced curb allows motor vehicles to cross it at low speed. Slope-faced curb is most often used on major suburban
thoroughfare A thoroughfare is a primary passage or way as a transit route through regularly trafficked areas, whether by road on dry land or, by extension, via watercraft or aircraft. On land, a thoroughfare may refer to anything from a multi-lane highwa ...
s. In certain locales, such as California, there is an effort to standardize the design to achieve efficiencies in construction and lower costs. Trends include using a gutter that balances the increased initial price with lower maintenance costs. At
crosswalk A pedestrian crossing (or crosswalk in American English) is a place designated for pedestrians to cross a road, street or avenue. The term "pedestrian crossing" is also used in the Vienna and Geneva Conventions, both of which pertain to road ...
s and other pedestrian crossings, narrow dropped
curb cut A curb cut (U.S.), curb ramp, depressed curb, dropped kerb ( UK), pram ramp, or kerb ramp ( Australia) is a solid (usually concrete) ramp graded down from the top surface of a sidewalk to the surface of an adjoining street. It is designed primaril ...
s are used to allow small wheeled vehicles such as
wheelchair A wheelchair is a chair with wheels, used when walking is difficult or impossible due to illness, injury, problems related to old age, or disability. These can include spinal cord injuries ( paraplegia, hemiplegia, and quadriplegia), cerebr ...
s, children's
tricycles A tricycle, sometimes abbreviated to trike, is a human-powered (or gasoline or electric motor powered or assisted, or gravity powered) three-wheeled vehicle. Some tricycles, such as cycle rickshaws (for passenger transport) and freight trikes ...
, prams, and strollers to cross. This makes it easier to traverse for some pedestrians, and especially for those in wheelchairs. Wider curb cuts are also used to allow motor vehicles to cross sidewalks at low speed, typically for
driveway A driveway (also called ''drive'' in UK English) is a type of private road for local access to one or a small group of structures, and is owned and maintained by an individual or group. Driveways rarely have traffic lights, but some that bear ...
s. In Great Britain, "high containment kerbs" are used at locations with pedestrians, fuel station pumps, and other areas that need greater protection from vehicle traffic. These are high - much higher than standard curb, with a sloped lower portion and a concave face. These are also known as "trief" curbs. Rounded curbs are most often used at driveways, and continuously along suburban residential streets where there are many driveways and the sidewalk has a grassy setback from the street. This type of curbing starts out nearly flat like the road, curves up in a
concave Concave or concavity may refer to: Science and technology * Concave lens * Concave mirror Mathematics * Concave function, the negative of a convex function * Concave polygon, a polygon which is not convex * Concave set * The concavity of a ...
manner to a gentle
slope In mathematics, the slope or gradient of a line is a number that describes both the ''direction'' and the ''steepness'' of the line. Slope is often denoted by the letter ''m''; there is no clear answer to the question why the letter ''m'' is use ...
, then curves back in a
convex Convex or convexity may refer to: Science and technology * Convex lens, in optics Mathematics * Convex set, containing the whole line segment that joins points ** Convex polygon, a polygon which encloses a convex set of points ** Convex polytop ...
manner to nearly flat again, making it much easier to drive over, and is also known as a "rolled" or "mountable curb" in some localities. These types of curbs are preferred by builders because they are less expensive than installing straight curbs and gutters. They are easier to lay using
concrete Concrete is a composite material composed of fine and coarse aggregate bonded together with a fluid cement (cement paste) that hardens (cures) over time. Concrete is the second-most-used substance in the world after water, and is the most wid ...
and require less forming as steel templates can be used with only front and back forms needed. Their use also eliminates the need for driveway cuts, curbs, and aprons, thus further reducing costs.


Material

Curbs are constructed of many materials, including asphalt, stone, or masonry blocks, but most often are made of
Portland cement Portland cement is the most common type of cement in general use around the world as a basic ingredient of concrete, mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in the early 19th ...
concrete. The type of material may depend on the type of paving material used for the road and the desired function or need. For example, a Portland concrete curb used with an asphalt concrete road surface provides a highly visible barrier at the edge of the road surface. Other types of curb material include stone slabs, cobblestone, and manufactured pavers. A concrete curb may be constructed by setting forms by hand, filling them, letting them set up, and then removing the forms. When large quantities of curb are to be constructed, it is often more efficient to use a slip form casting machine. Curbs can also be
precast Precast concrete is a construction product produced by casting concrete in a reusable mold or "form" which is then cured in a controlled environment, transported to the construction site and maneuvered into place; examples include precast bea ...
at a central location and trucked to the construction site. Asphalt curb is usually made with a paving machine. It can be cheaper if it is formed at the same time that a road is paved, but is less durable than a concrete curb. Stone curb, often made from
granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies under ...
, is durable and resistant to de-icing salt. It is also chosen for aesthetic reasons. In areas where granite is available, it may be cheaper than concrete curb. One disadvantage of granite curb is that it can cut a tire sidewall if it is rough-faced. Belgian block curbs are made by placing blocks over a concrete slip. Then, more concrete is wedged in between the blocks to hold them together. These blocks can be vertical or angled in order to create a mountable curb.


Height

When designing a curbed roadway, engineers specify the "reveal" or "lip". The reveal is the height of the section that is visible (revealed) above the road surface. Typical reveals are in the range. Curbs at handicapped curb cuts (or "kerb ramps", for example in Australia) should have no reveal. One of the recommendations has been using a 4/12 batter in to accommodate automobile design because steeper batters tend to interfere with body trim, hubcaps, and lower door edges while curb faces in excess of in height may prevent the full opening of car doors. Most curb extends down into the ground below the pavement surface, to improve their stability over time. The total height, including the buried portion, is often .


Integral gutter

Curbs with integral gutters are used where better hydraulic flow performance is needed. However, this places a longitudinal joint (parallel to the direction of travel) near where
bicyclists Cycling, also, when on a two-wheeled bicycle, called bicycling or biking, is the use of cycles for transport, recreation, exercise or sport. People engaged in cycling are referred to as "cyclists", "bicyclists", or "bikers". Apart from two ...
often ride. If the main roadway and gutter settle differently over time, the vertical edge that develops at the joint can cause a hazard for bicyclists.


Paint

Curbs are in some places painted to increase visibility or mark a special street side.


Auto racing curbs

In auto racing, curbs are flat curbstones lining the corners or
chicanes A chicane () is a serpentine curve in a road, added by design rather than dictated by geography. Chicanes add extra turns and are used both in motor racing and on roads and streets to slow traffic for safety. For example, one form of chicane is ...
of racing tracks. They are often painted red and white, and are intended to prevent unauthorized short-cuts and keep the racers safely on the track. Although they are not considered part of the racing track, drivers sometimes "ride the curbs" in order to maintain momentum and gain a time advantage in cornering.


Cultural identifiers

In certain parts of the world, curb design signifies cultural association. For example, in countries of the former
Portuguese Empire The Portuguese Empire ( pt, Império Português), also known as the Portuguese Overseas (''Ultramar Português'') or the Portuguese Colonial Empire (''Império Colonial Português''), was composed of the overseas colonies, factories, and the ...
, such as
Brazil Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
, curbs are often distinctively decorated (along with the footpaths more broadly) in a style known as
Portuguese pavement Portuguese may refer to: * anything of, from, or related to the country and nation of Portugal ** Portuguese cuisine, traditional foods ** Portuguese language, a Romance language *** Portuguese dialects, variants of the Portuguese language ** Portu ...
, marking a clear link to Portugal, where the style originated. More explicitly, curbstones can be painted (by official sanction or otherwise) to stress an identity or ideology; for instance, in
Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...
, curbstones are frequently painted in communities to identify a religious/political affiliation – typically either red, white, and blue for Unionist/Loyalist areas, and green, white, and orange for
Nationalist Nationalism is an idea and movement that holds that the nation should be congruent with the state. As a movement, nationalism tends to promote the interests of a particular nation (as in a group of people), Smith, Anthony. ''Nationalism: Th ...
areas.


See also

*
Curb appeal Curb appeal is attractiveness of the exterior of a residential or commercial property, as viewed from the street. The term was extensively used in the United States during the housing boom and continues to be used as an indicator of the initial ...
* Curb extension *
Curb feeler Curb feelers or curb finders are springs or wires installed on a vehicle which act as "whiskers" to alert drivers when they are at the right distance from the curb while parking. The devices are fitted low on the body, close to the wheels. As ...
* Kassel kerb * Road surface *
Curb stomp A curb stomp, also called curbing, curb checking, curb painting, or making someone bite the curb is a form of assault in which a victim's mouth is forcefully placed on a curb and then stomped from behind, causing severe injuries and sometimes dea ...
*
Kerbside collection Kerbside collection or curbside collection is a service provided to households, typically in urban and suburban areas, of collecting and disposing of household waste and recyclables. It is usually accomplished by personnel using specially built ...


References

{{Authority control Road infrastructure Road hazards