A curb (American English) or kerb (British English) is the edge where a raised sidewalk or road median/central reservation meets a street or other roadway.
A curb (American English) or kerb (British English) is the edge where a raised sidewalk 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, [1] 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. [2]
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. [3]
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 roads in the early 19th-century, curbs became ubiquitous in the streets of London. [4]
Curbs present an obstacle for accessibility to physically disabled persons in public spaces. [5] In 1945, Jack Fisher of Kalamazoo, Michigan, celebrated the installation of one of the nation's first curb cuts to facilitate mobility in the center of the city. [5] 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. [5]
Curbs may fulfill any or several of a number of functions. [6] 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 drains.
There is also an aesthetic aspect, in that curbs look formal and "finished".[ citation needed ]
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 and can provide some redirective capacity for low-speed impacts. [6]
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. [6]
A high-speed vehicle that hits a curb may actually turn towards the sidewalk, rather than be directed away from it. [6] A vehicle that strikes a curb can also be tripped into a rollover crash or vaulted into the air. [7] 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. [8]
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 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. [9] 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. [9]
There are a number of types of curbs, categorized by shape, material, height, and whether the curb is combined with a gutter. 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.
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.[ citation needed ] 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 thoroughfares.
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 24-inch (610 mm) gutter that balances the increased initial price with lower maintenance costs. [10]
At crosswalks and other pedestrian crossings, narrow dropped curb cuts are used to allow small wheeled vehicles such as wheelchairs, 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 driveways.
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 14 inches (36 cm) high - much higher than standard curb, with a sloped lower portion and a concave face. These are also known as "trief" curbs. [11]
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 manner to a gentle slope, then curves back in a convex 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. [12] They are easier to lay using concrete and require less forming as steel templates can be used with only front and back forms needed. [12] Their use also eliminates the need for driveway cuts, curbs, and aprons, thus further reducing costs. [12]
Curbs are 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 road surface provides a highly visible barrier at the edge of the road surface. Other types of curb material include stone slabs, cobblestone, 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.[ citation needed ]
Stone curb, often made from granite, 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. [13] One disadvantage of granite curb is that it can cut a tire sidewall if it is rough-faced. [14]
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.
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 4 to 8 inches (100 to 200 mm) range. Curbs at handicapped curb cuts (or "kerb ramps", for example in Australia) should have no reveal. [15] 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 6 in (152 mm) in height may prevent the full opening of car doors. [10] 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 16 in (406 mm). [16]
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 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. [17]
In some places curbs are painted to increase visibility or mark a special street side.
In auto racing, curbs are flat curbstones lining the corners or chicanes of racing tracks. [18] 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, [19] drivers sometimes "ride the curbs" in order to maintain momentum and gain a time advantage in cornering. [18]
In certain parts of the world, curb design signifies cultural association. For example, in countries of the former Portuguese Empire, such as Brazil, curbs are often distinctively decorated (along with the footpaths more broadly) in a style known as Portuguese pavement, 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, 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 areas. [20] [21]
A road is a thoroughfare for the conveyance of traffic that mostly has an improved surface for use by vehicles and pedestrians. Unlike streets, whose primary function is to serve as public spaces, the main function of roads is transportation.
A sidewalk, pavement, footpath in Australia, India, New Zealand and Ireland, or footway is a path along the side of a road. Usually constructed of concrete, pavers, brick, stone, or asphalt, it is designed for pedestrians. A sidewalk is normally higher than the roadway, and separated from it by a kerb. There may also be a planted strip between the sidewalk and the roadway and between the roadway and the adjacent land.
A curb cut (U.S.), curb ramp, depressed curb,dropped kerb (UK), pram ramp, or kerb ramp (Australia) is a solid ramp graded down from the top surface of a sidewalk to the surface of an adjoining street. It is designed primarily for pedestrian usage and commonly found in urban areas where pedestrian activity is expected. In comparison with a conventional curb a curb cut is finished at an intermediate gradient that connects both surfaces, sometimes with tactile paving.
Pavement or paving may refer to:
Traffic calming uses physical design and other measures to improve safety for motorists, car drivers, pedestrians and cyclists. It has become a tool to combat speeding and other unsafe behaviours of drivers. It aims to encourage safer, more responsible driving and potentially reduce traffic flow. Urban planners and traffic engineers have many strategies for traffic calming, including narrowed roads and speed humps. Such measures are common in Australia and Europe, but less so in North America. Traffic calming is a calque of the German word Verkehrsberuhigung – the term's first published use in English was in 1985 by Carmen Hass-Klau.
A street is a 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 surface such as tarmac, concrete, cobblestone or brick. Portions may also be smoothed with asphalt, embedded with rails, or otherwise prepared to accommodate non-pedestrian traffic.
A 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, gravel road surfaces, macadam, hoggin, cobblestone and granite setts were extensively used, but these have mostly been replaced by asphalt or concrete laid on a compacted base course. Asphalt mixtures have been used in pavement construction since the beginning of the 20th century and are of two types: metalled (hard-surfaced) and unmetalled roads. Metalled roadways are made to sustain vehicular load and so are usually made on frequently used roads. Unmetalled roads, also known as gravel roads or dirt roads, are rough and can sustain less weight. Road surfaces are frequently marked to guide traffic.
Asphalt concrete is a composite material commonly used to surface roads, parking lots, airports, and the core of embankment dams. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. It consists of mineral aggregate bound together with bitumen, laid in layers, and compacted.
A curb extension is a traffic calming measure which widens the sidewalk for a short distance. This reduces the crossing distance and allows pedestrians and drivers to see each other when parked vehicles would otherwise block visibility. The practice of banning car parking near intersections is referred to as daylighting the intersection.
Permeable paving surfaces are made of either a porous material that enables stormwater to flow through it or nonporous blocks spaced so that water can flow between the gaps. Permeable paving can also include a variety of surfacing techniques for roads, parking lots, and pedestrian walkways. Permeable pavement surfaces may be composed of; pervious concrete, porous asphalt, paving stones, or interlocking pavers. Unlike traditional impervious paving materials such as concrete and asphalt, permeable paving systems allow stormwater to percolate and infiltrate through the pavement and into the aggregate layers and/or soil below. In addition to reducing surface runoff, permeable paving systems can trap suspended solids, thereby filtering pollutants from stormwater.
Cobblestone is a natural building material based on cobble-sized stones, and is used for pavement roads, streets, and buildings. Setts, also called Belgian blocks, are often referred to as "cobbles", although a sett is distinct from a cobblestone by being quarried and shaped into a regular form, while cobblestones are naturally occurring forms less uniform in size.
A driveway is a private road for local access to one or a small group of structures owned and maintained by an individual or group.
Standards for Interstate Highways in the United States are defined by the American Association of State Highway and Transportation Officials (AASHTO) in the publication A Policy on Design Standards: Interstate System. For a certain highway to be considered an Interstate Highway, it must meet these construction requirements or obtain a waiver from the Federal Highway Administration.
Tactile paving is a system of textured ground surface indicators found at roadsides, by and on stairs, and on railway station platforms, to assist pedestrians who are vision impaired.
Traffic barriers keep vehicles within their roadway and prevent them from colliding with dangerous obstacles such as boulders, sign supports, trees, bridge abutments, buildings, walls, and large storm drains, or from traversing steep (non-recoverable) slopes or entering deep water. They are also installed within medians of divided highways to prevent errant vehicles from entering the opposing carriageway of traffic and help to reduce head-on collisions. Some of these barriers, designed to be struck from either side, are called median barriers. Traffic barriers can also be used to protect vulnerable areas like school yards, pedestrian zones, and fuel tanks from errant vehicles. In pedestrian zones, like school yards, they also prevent children or other pedestrians from running onto the road.
A street gutter is a depression that runs parallel to a road and is designed to collect rainwater that flows along the street diverting it into a storm drain. A gutter alleviates water buildup on a street, allows pedestrians to pass without walking through puddles, and reduces the risk of hydroplaning by road vehicles. When a curbstone is present, a gutter may be formed by the convergence of the road surface and the vertical face of the sidewalk; otherwise, a dedicated gutter surface made of concrete may be present. Depending on local regulations, a gutter usually discharges, as a nonpoint pollution source in a storm drain whose final discharge falls into a detention pond or into a body of water. Street gutters are most often found in areas of a city which have high pedestrian traffic. In rural areas, gutters are seldom used and are frequently replaced by a borrow ditch.
A snowmelt system prevents the build-up of snow and ice on cycleways, walkways, patios and roadways, or more economically, only a portion of the area such as a pair of 2-foot (0.61 m)-wide tire tracks on a driveway or a 3-foot (0.91 m) center portion of a sidewalk, etc. It is also used to keep entire driveways and patios snow free in snow prone climates. The "snow melt" system is designed to function during a storm to improve safety and eliminate winter maintenance labor including shoveling, plowing snow and spreading de-icing salt or traction grit (sand). A snowmelt system may extend the life of the concrete, asphalt or under pavers by eliminating the use of salts or other de-icing chemicals, and physical damage from winter service vehicles. Many systems are fully automatic and require no human input to maintain a snow/ice-free horizontal surface.
Road traffic collisions generally fall into one of five common types:
Terminology related to road transport—the transport of passengers or goods on paved routes between places—is diverse, with variation between dialects of English. There may also be regional differences within a single country, and some terms differ based on the side of the road traffic drives on. This glossary is an alphabetical listing of road transport terms.
A stroad is a type of street–road hybrid. Common in the United States and Canada, stroads are wide arterials that often provide access to strip malls, drive-throughs, and other automobile-oriented businesses. Stroads have been criticized by urban planners for their safety issues and inefficiencies. While streets serve as a destination and provide access to shops and residences at safe traffic speeds, and roads serve as a high-speed connection that can efficiently move traffic at high speed and volume, stroads are often expensive, inefficient, and dangerous.
20.2 Drivers must use the track at all times. For the avoidance of doubt the white lines defining the track edges are considered to be part of the track but the kerbs are not.
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