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A curb (American English) or kerb (British English) is the edge where a raised sidewalk/Sidewalk or road median meets a street/other roadway.
A series of Paving Acts in the 18th century, especially the 1766 Paving and Lighting Act, authorized the City of London Corporation to create footways along the streets of London, pave them with Purbeck stone (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 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 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 (ADA) have facilitated travel for wheelchair users and other people.
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 ) make them necessary. Curbs are not universally used, however, even in urban settings (see living street).
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 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 Vehicle rollover crash or vaulted into the air.To be tripped into a rollover, a vehicle generally must slide into the curb at least partly sideways, so that the leading wheels that are sliding on the road catch on the curb; then the wheels cannot pass over the curb, but if the upper body of the vehicle is moving fast enough, it will continue over the curb, so that the vehicle will rotate (roll) on an axis more or less parallel to the curb. The minimum speed for this to happen in a given curb-collision scenario gets lower as the height of the vehicle's center of gravity—including its load—gets higher. The vehicle could be vaulted over a traffic barrier 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. retroreflector road marking 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.
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 and other pedestrian crossings, narrow dropped are used to allow small wheeled vehicles such as , children's tricycles, 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 .
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 manner to a gentle slope, then curves back in a 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 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.
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 forming casting machine. Curbs can also be Precast concrete 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, is durable and resistant to Road salt. It is also chosen for aesthetic reasons. In areas where granite is available, it may be cheaper than concrete curb. (2025). 9781560512639, American Society of State Highway and Transportation Officials. . ISBN 9781560512639 One disadvantage of granite curb is that it can cut a tire 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.
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