Curb (road)

A curb (North American English), or kerb (British English), is the edge where a raised sidewalk (pavement in British English) or road median/central reservation meets a street or other roadway.

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 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. Previously, small wooden bollards had been put up to demarcate the area of the street reserved for pedestrian use. 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.

With the introduction of macadam roads in the early 19th-century, curbs became ubiquitous in the streets of London.

Curbs may fulfill any or several of a number of functions. 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).

In low-speed environments, curbs are effective at channeling 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 crash or vaulted into the air. 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 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.

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