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A curb (
American English American English, sometimes called United States English or U.S. English, is the set of variety (linguistics), varieties of the English language native to the United States. English is the Languages of the United States, most widely spoken lang ...
) or kerb (
British English British English is the set of Variety (linguistics), varieties of the English language native to the United Kingdom, especially Great Britain. More narrowly, it can refer specifically to the English language in England, or, more broadly, to ...
) is the edge where a raised
sidewalk A sidewalk (North American English), pavement (British English, South African English), or footpath (Hiberno-English, Irish English, Indian English, Australian English, New Zealand English) is a path along the side of a road. Usually constr ...
/pavement or road median/central reservation meets a street/other roadway.


History

Although curbs have been used throughout modern history, and indeed were present in ancient
Pompeii Pompeii ( ; ) was a city in what is now the municipality of Pompei, near Naples, in the Campania region of Italy. Along with Herculaneum, Stabiae, and Villa Boscoreale, many surrounding villas, the city was buried under of volcanic ash and p ...
, 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 local authority of the City of London, the historic centre of London and the location of much of the United Kingdom's f ...
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
bollard A bollard is a sturdy, short, vertical post. The term originally referred to a post on a ship or quay used principally for mooring boats. In modern usage, it also refers to posts installed to control road traffic and posts designed to pre ...
s 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 Kalamazoo ( ) is a city in Kalamazoo County, Michigan, United States, and its county seat. At the 2020 United States census, 2020 census, Kalamazoo had a population of 73,598. It is the principal city of the Kalamazoo–Portage metropolitan are ...
, 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 mobilized form of chair using two or more wheels, a footrest, and an armrest usually cushioned. It is used when walking is difficult or impossible to do due to illnesses, injury, disabilities, or age-related health conditio ...
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 drain A storm drain, storm sewer (United Kingdom, U.S. and Canada), highway drain, surface water drain/sewer (United Kingdom), or stormwater drain (Australia and New Zealand) is infrastructure designed to drain excess rain and ground water from i ...
s. 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
culvert A culvert is a structure that channels water past an obstacle or to a subterranean waterway. Typically embedded so as to be surrounded by soil, a culvert may be made from a pipe (fluid conveyance), pipe, reinforced concrete or other materia ...
s) make them necessary. Curbs are not universally used, however, even in urban settings (see
living street A living street or residential street is a street designed with the interests of pedestrians and Cycling, cyclists in mind. Living streets also act as social spaces, allowing children to play and encouraging social interactions on a human scale, ...
).


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 Surface runoff, water flow or wind) that removes soil, Rock (geology), rock, or dissolved material from one location on the Earth's crust#Crust, Earth's crust and then sediment transport, tran ...
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 (known in North America as guardrails or guard rails, in Britain as crash barriers, and in auto racing as Armco barriers AK Steel (formerly Armco) genericized trademark) keep vehicles within their roadway and prevent them from co ...
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 light or other radiation back to its source with minimum scattering. This works at a wide range of angle of incidence, unlike a planar mirror, w ...
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 Film * ''The Gutter'' (1938 film), a French film * ''The Gutter'' (2024 film), an American film Design and p ...
. 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 of transport, whether by road on dry land or, by extension, via watercraft or aircraft. Originally, the word referred to a main road or open street which was frequented thoroughly. Different terms *Roa ...
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 crosswalks and other
pedestrian crossing A pedestrian crossing (or crosswalk in American and Canadian English) is a place designated for pedestrians to cross a road, street or Avenue (landscape), avenue. The term "pedestrian crossing" is also used in the Vienna Convention on Road Sign ...
s, 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 mobilized form of chair using two or more wheels, a footrest, and an armrest usually cushioned. It is used when walking is difficult or impossible to do due to illnesses, injury, disabilities, or age-related health conditio ...
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 private road for local access to one or a small group of structures owned and maintained by an individual or group. Driveways rarely have traffic lights, but some may if they handle heavy ...
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 simple polygon that is not convex is called concave, non-convex or ...
manner to a gentle
slope In mathematics, the slope or gradient of a Line (mathematics), line is a number that describes the direction (geometry), direction of the line on a plane (geometry), plane. Often denoted by the letter ''m'', slope is calculated as the ratio of t ...
, 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 aggregate bound together with a fluid cement that cures to a solid over time. It is the second-most-used substance (after water), the most–widely used building material, and the most-manufactur ...
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 (masonry), mortar, stucco, and non-specialty grout. It was developed from other types of hydraulic lime in England in th ...
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 Cobblestone is a natural building material based on Cobble (geology), cobble-sized stones, and is used for Road surface, pavement roads, streets, and buildings. Sett (paving), Setts, also called ''Belgian blocks'', are often referred to as " ...
, 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 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 (phanerite, phaneritic) intrusive rock, 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 coo ...
, 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 A sett, also known as a block or Belgian block, is a broadly rectangular quarry, quarried Rock (geology), stone used in Road surface, paving roads and walkways. Formerly in widespread use, particularly on steeper streets because setts provide ...
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. File:Curb metal forms under construction.jpg, Metal forms before the concrete is poured and finished by hand File:Curbhandform.jpg, Hand forming at catch basins


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 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 (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 known as bicycling or biking, is the activity of riding a bicycle or other types of pedal-driven human-powered vehicles such as balance bikes, unicycles, tricycles, and quadricycles. Cycling is practised around the world for pur ...
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

In some places curbs are 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 was a colonial empire that existed between 1415 and 1999. In conjunction with the Spanish Empire, it ushered in the European Age of Discovery. It achieved a global scale, controlling vast portions of the Americas, Africa ...
, such as
Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...
, curbs are often distinctively decorated (along with the footpaths more broadly) in a style known as
Portuguese pavement Portuguese pavement, known in Portuguese as or simply (or in Brazil), is a traditional-style pavement used for many pedestrian areas in Portugal. It consists of small pieces of stone arranged in a pattern or image, like a mosaic. It can also ...
, 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 ( ; ) is a Countries of the United Kingdom, part of the United Kingdom in the north-east of the island of Ireland. It has been #Descriptions, variously described as a country, province or region. Northern Ireland shares Repub ...
, 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 or movement that holds that the nation should be congruent with the State (polity), state. As a movement, it presupposes the existence and tends to promote the interests of a particular nation,Anthony D. Smith, Smith, A ...
areas.


See also

* Curb appeal *
Curb cut effect The curb cut effect is the phenomenon of disability-friendly features being used and appreciated by a larger group than the people they were designed for. The phenomenon is named for curb cuts miniature ramps comprising parts of sidewalk which wer ...
*
Curb extension A curb extension (or also neckdown, kerb extension, bulb-out, bump-out, kerb build-out, nib, elephant ear, curb bulge, curb bulb, or blister) is a traffic calming measure which widens the sidewalk for a short distance. This reduces the crossi ...
*
Curb feeler Curb feelers or curb finders are springs or wires installed on a vehicle that 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 t ...
*
Curb stomp A curb stomp, also called curbing, curb painting, or making someone bite the curb, is a form of grievous assault or attempted murder in which a victim's jaw is forcefully placed on a curb and then stomped from behind, causing severe injuries or d ...
*
Kassel kerb A Kassel kerb is a design of kerb (curb in US English) that features a concave-section that allows for an easier alignment for buses. The kerb was first introduced in the German city of Kassel for the low-floor tram system but has since been a ...
* Kerb guidance *
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 buil ...
*
Road surface A road surface (British English) or pavement (North American English) is the durable surface material laid down on an area intended to sustain vehicular or foot traffic, such as a road or walkway. In the past, gravel road surfaces, macadam, ...
* Wheel chock#Parking chocks—Curbs for parking spaces


References


External links

* {{Authority control Road hazards Road infrastructure