Curb

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (October 2008)

Curb, gutter, and storm drain

Metal forms before the concrete is poured and finished by hand.

A road side curb.

Old pavement with granite curb in Kutná Hora

Curb construction using a slip form casting machine

Hand forming at catch basins

A curb or kerb (see spelling differences) is the edge where a raised pavement/sidewalk/footpath, road median, or road shoulder meets an unraised street or other roadway. Typically made from concrete, asphalt, or long stones (often granite), the purpose is twofold: first as a gutter for proper drainage of the roadway, and second for safety, to prevent motorists from driving onto the shoulder, median, sidewalk, or pavement.

Function

Curbs guide water from melted snow, rain, and ice into storm drains, so that it does not gather on the road. Big puddles can be dangerous, because they can cause hydroplaning at higher speeds and loss of control of a vehicle. At lower speeds, water can spray from tires onto following vehicles, causing poor visibility. Also pedestrians can be splashed by water.

Curbs also keep vehicles on the road and prevent people from using sidewalks as a hard shoulder.

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 addition to driveway aprons, curbs also slope down to street level at crosswalks and other pedestrian crossings. This is called a curb cut (U.S.), dropped kerb (UK), pram ramp (Australia), or dish (Ireland). This makes it easier to traverse for pedestrians, and especially for those in wheelchairs, or for people with prams and strollers.

Depending on the area, the white line that normally indicates the outside (shoulder) edge of the road may or may not be present where there is a curb.

Variations

There are a number of types of curb - basic curb (the pavement abuts the curb without a gutter), combined curb and gutter (also called curb and channel - may be rolled, traversable, or barrier) and integral curb (curb constructed integrally as a part of a concrete pavement).

Typical types of curb based on the cross sectional shape: insurmountable, rolled, or rounded (used in many residential areas), surmountable or traversable (used along islands at intersections allowing errant vehicles to cross), and barrier ("L" shaped and used as a boundary to prevent vehicle from exiting the pavement).

Curbs may be squared-off, angled, or rounded. 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 starts out nearly flat like the road, curves up in a concave manner to a gentle slope, 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. The angled type is most often used on major suburban thoroughfares, and is more modern than the other two. The square (90°-edge) 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.

Curbs may be constructed of many materials but most often are made of concrete or asphalt. 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 concrete curb used with an asphalt pavement provides a highly visible barrier at the edge of the pavement. Other types of curb material include stone slab, cobblestone, and manufactured pavers.

Construction

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. Belgium Block curbs used in north New Jersey, are made by placing blocks over a concrete slip. Then, concrete is wedged in between each block to hold them together. In newer subdivisions, these blocks are angled in order to create a mountable curb.

See also

• Curb extension
• Curb feeler
• Driveway
• Kassel kerb
• Living street
• Pavement (material)

References