A curb, or kerb is the edge where a raised pavement/sidewalk/footpath

Sidewalk

A sidewalk, or pavement, footpath, footway, and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade and is normally separated from the vehicular section by a curb...

, road median, or road shoulder meets an unraised street

Street

A street is a paved public thoroughfare in a built environment. It is a public parcel of land adjoining buildings in an urban context, on which people may freely assemble, interact, and move about. A street can be as simple as a level patch of dirt, but is more often paved with a hard, durable...

 or other 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...

way.

Function

Curbs may fulfill any or several of a number of functions. They separate the road from the roadside, discouraging 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

Water

Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...

 from rain

Rain

Rain is liquid precipitation, as opposed to non-liquid kinds of precipitation such as snow, hail and sleet. Rain requires the presence of a thick layer of the atmosphere to have temperatures above the melting point of water near and above the Earth's surface...

, or melted snow

Snow

Snow is a form of precipitation within the Earth's atmosphere in the form of crystalline water ice, consisting of a multitude of snowflakes that fall from clouds. Since snow is composed of small ice particles, it is a granular material. It has an open and therefore soft structure, unless packed by...

 and ice

Ice

Ice is water frozen into the solid state. Usually ice is the phase known as ice Ih, which is the most abundant of the varying solid phases on the Earth's surface. It can appear transparent or opaque bluish-white color, depending on the presence of impurities or air inclusions...

 into storm drain

Storm drain

A storm drain, storm sewer , stormwater drain or drainage well system or simply a drain or drain system is designed to drain excess rain and ground water from paved streets, parking lots, sidewalks, and roofs. Storm drains vary in design from small residential dry wells to large municipal systems...

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

Urban area

An urban area is characterized by higher population density and vast human features in comparison to areas surrounding it. Urban areas may be cities, towns or conurbations, but the term is not commonly extended to rural settlements such as villages and hamlets.Urban areas are created and further...

 and 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 are rarely found in rural

Rural

Rural areas or the country or countryside are areas that are not urbanized, though when large areas are described, country towns and smaller cities will be included. They have a low population density, and typically much of the land is devoted to agriculture...

 areas except where certain drainage conditions (such as mountain

Mountain

Image:Himalaya_annotated.jpg|thumb|right|The Himalayan mountain range with Mount Everestrect 58 14 160 49 Chomo Lonzorect 200 28 335 52 Makalurect 378 24 566 45 Mount Everestrect 188 581 920 656 Tibetan Plateaurect 250 406 340 427 Rong River...

s or culvert

Culvert

A culvert is a device used to channel water. It may be used to allow water to pass underneath a road, railway, or embankment. Culverts can be made of many different materials; steel, polyvinyl chloride and concrete are the most common...

s) make them necessary. Curbs are not universally used, however, even in urban settings (see living street

Living street

A living street is a street in which, unlike in most 20th century streets, the needs of car drivers are secondary to the needs of users of the street as a whole. It is a space designed to be shared by pedestrians, playing children, bicyclists, and low-speed motor vehicles...

).

Safety

In low-speed environments, curbs are effective at channelizing motor vehicle traffic. On higher speed roads, curbs should not be used because they can destabilize vehicles that strike them. 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 be tripped into a rollover

Rollover

A rollover is a type of vehicle accident in which a vehicle tips over onto its side or roof. The most common cause of a rollover is traveling too fast while turning.- Dynamics :Vehicles can roll over in several ways...

 crash or vaulted into the air. The vehicle could be vaulted over a traffic barrier

Traffic barrier

Traffic barriers keep vehicles within their roadway and prevent vehicles from colliding with dangerous obstacles. Traffic barriers installed at the road side also prevent errant vehicles from traversing steep slopes. Traffic barriers installed at the medians of divided highways are also referred...

 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 curb is used with a traffic barrier, the barrier should 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 pavement, the white edge line that normally indicates the outside (shoulder) edge of the road may or may not be present where there is a curb. Reflectorized road marking material can also be applied to the curb itself to make it more conspicuous.

Types of curb

There are a number of types of curb, categorized by shape, material, height, and by whether the curb is combined with a gutter. Most curb is constructed separately from the pavement, and the gutter is formed by the joint between the gutter and the curb. Combined curb and gutter (also called curb and channel) has a concrete curb and gutter cast together in one piece. Integral curb is curb constructed integrally as a part of a concrete pavement.

Shape

Curb often have a vertical or nearly-vertical face, also called barrier, nonmountable or insurmountable curb. Vertical faced curb is used to discourage motor vehicle drivers from leaving the roadway. The square (90°-edge) type is still almost always used in town

Town

A town is a human settlement larger than a village but smaller than a city. The size a settlement must be in order to be called a "town" varies considerably in different parts of the world, so that, for example, many American "small towns" seem to British people to be no more than villages, while...

s and cities, as it is a straight step down and thus less likely to be tripped-over by pedestrians. Slope faced curb allows vehicles to cross it at low speed. Slope-faced curb is most often used on major suburban thoroughfare

Thoroughfare

A thoroughfare is a place of transportation intended to connect one location to another. Highways, roads, and trails are examples of thoroughfares used by a variety of general traffic. On land a thoroughfare may refer to anything from a rough trail to multi-lane highway with grade separated...

s. At driveways, crosswalks and other pedestrian crossing

Pedestrian crossing

A pedestrian crossing or crosswalk is a designated point on a road at which some means are employed to assist pedestrians wishing to cross. They are designed to keep pedestrians together where they can be seen by motorists, and where they can cross most safely across the flow of vehicular traffic...

s, dropped curb cut

Curb cut

A curb cut , curb ramp, dropped kerb , pram ramp, or kerb ramp is a solid ramp graded down from the top surface of a sidewalk to the surface of an adjoining street. It is designed for pedestrian uses and commonly found in urban areas where pedestrian activity is expected...

s are used to allow wheeled vehicles such as automobiles, wheelchairs, prams and strollers to cross it. This makes it easier to traverse for pedestrians, and especially for those in wheelchair

Wheelchair

A wheelchair is a chair with wheels, designed to be a replacement for walking. The device comes in variations where it is propelled by motors or by the seated occupant turning the rear wheels by hand. Often there are handles behind the seat for someone else to do the pushing...

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 350 millimetres (13.8 in) high - much higher than standard curb, with a sloped lower portion and a concave face. These are also known as "Trief" or "Titan" curbs.

Rounded curbs are most often used at driveway

Driveway

A driveway 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....

s, and continuously along suburban residential streets where there are many driveways and the sidewalk has a grassy setback from the street. This type starts out nearly flat like the road, curves up in a concave manner to a gentle slope

Slope

In mathematics, the slope or gradient of a line describes its steepness, incline, or grade. A higher slope value indicates a steeper incline....

, then curves back in a convex manner to nearly flat again, making it much easier to drive over, and are also known as mountable curbs in some localities.

Material

Curbs may be constructed of many materials, including asphalt, stone or masonry blocks, but most often are made of Portland cement 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 pavement provides a highly visible barrier at the edge of the pavement. Other types of curb material include stone slab, cobblestone

Cobblestone

Cobblestones are stones that were frequently used in the pavement of early streets. "Cobblestone" is derived from the very old English word "cob", which had a wide range of meanings, one of which was "rounded lump" with overtones of large size...

, and manufactured pavers

Paver (flooring)

An interlocking concrete paver is a pre-cast piece of concrete or brick commonly used in exterior hardscaping applications. Pavers were developed in Europe and introduced into the United States in the early 1970s....

.

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

Slip forming

This article is about pouring concrete in moving forms. See Slipform stonemasonry for another type of slip forming.Slip forming, continuous poured, continuously formed, or slipform construction is a construction method in which concrete is poured into a continuously moving form...

 casting machine. Curbs can also be precast

Precast concrete

By producing precast concrete in a controlled environment , the precast concrete is afforded the opportunity to properly cure and be closely monitored by plant employees. Utilizing a Precast Concrete system offers many potential advantages over site casting of concrete...

 at a central location and trucked to the construction site.

Asphalt curb is 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 concrete curb.

Stone curb, often made from granite, is durable and resistant to deicing salt. It is also chosen for aesthetic reasons. In areas where granite is available, it may be cost-competitive with concrete curb. One disadvantage is granite curb can cut a tire sidewall if rough-faced curb is used.

Belgian block curbs are made by placing blocks over a concrete slip. Then, concrete is wedged in between each block 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. Most curb extends down into the ground next to the pavement edge. The reveal is the height of the section that is visible (revealed) above the pavement surface. Typical reveals are in the 4 to 8 in (101.6 to 203.2 mm) range. Curbs at handicapped curb cuts should have no reveal, although Americans with Disabilities Act guidelines permit up to 0.25 inches (6.4 mm) of vertical reveal.

Integral gutter

Curbs with integral gutters are used where better hydraulic flow performance is needed. However, this places a longitudinal joint near where bicyclists

Bicycle

A bicycle, also known as a bike, pushbike or cycle, is a human-powered, pedal-driven, single-track vehicle, having two wheels attached to a frame, one behind the other. A person who rides a bicycle is called a cyclist, or bicyclist....

 often ride. If the pavement and gutter settle differently over time, the vertical edge that developes at the joint can cause a hazard for bicyclists.

See also

• Curb extension
  Curb extension
  A curb extension is a traffic calming measure, primarily used to extend the sidewalk, reducing the crossing distance and allowing pedestrians about to cross and approaching vehicle drivers to see each other when vehicles...
  
  
• Curb feeler
  Curb feeler
  Curb feelers or curb finders are springs or wires installed on a vehicle which act as "whiskers" to warn drivers that they are too close to the curb or other obstruction.The devices are fitted low on the body, close to the wheels...
  
  
• Driveway
  Driveway
  A driveway 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....
  
  
• Kassel kerb
  Kassel kerb
  A Kassel kerb is a concave-section made for buses kerb stone which is intended for use at bus stops served by modern low floor buses which have improved accessibility for mobility-impaired people....
  
  
• Living street
  Living street
  A living street is a street in which, unlike in most 20th century streets, the needs of car drivers are secondary to the needs of users of the street as a whole. It is a space designed to be shared by pedestrians, playing children, bicyclists, and low-speed motor vehicles...
  
  
• Pavement (material)
  Pavement (material)
  Road surface or pavement 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 cobblestones and granite setts were extensively used, but these surfaces have mostly been replaced by asphalt or concrete. Such...