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A sidewalk (or pavement in British English), (footpath, footway in Australian and New Zealand English), and sometimes platform, is a path along the side of a road. A sidewalk may accommodate moderate changes in grade (height) and is normally separated from the vehicular section by a curb (British English: kerb). There may also be a road verge (a strip of vegetation, grass or bushes or trees or a combination of these, referred to as either a verge or a nature strip in Australia) either between sidewalk and the roadway (British English: carriageway) or between the sidewalk and the boundary.
In the United States, the term sidewalk is used for the pedestrian path beside a road. shared-use path and multi-use path is reserved for use for ones available for use by both pedestrians and bicyclists. Walkway is a more comprehensive term that includes stairs, ramps, passageways, and related structures that facilitate the use of a path as well as the sidewalk.
There is evidence that sidewalks were built in ancient times. It was claimed that the Greek city of Corinth was paved by the 4th-century, and the Romans were particularly prolific sidewalk builders - they called them semitas.
However, by the Middle Ages, narrow roads had reverted to being simultaneously used by pedestrians and wagons, without any formal separation between the two categories. Early attempts at ensuring the adequate maintenance of sidewalks were often made, such as the 1623 Act for Colchester, although they were generally not very effective.
Following the Great Fire of London in 1666, attempts were slowly made to bring some order to the sprawling city. In 1671, 'Certain Orders, Rules and Directions Touching the Paving and Cleansing The Streets, Lanes and Common Passages within the City of London' were formulated, calling for all streets to be adequately paved for pedestrians with cobblestones. Purbeck stone was widely used as a durable paving material. Bollards were also installed to protect pedestrians from the traffic in the middle of the road.
A series of Paving Acts from the House of Commons during the 18th century, especially the 1766 Paving & Lighting Act, authorized the City of London Corporation to create foot-ways along all the streets of London, to pave them with Purbeck stone (the thoroughfare in the middle was generally cobblestone) and to raise them above the 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. By the late 19th-century large and spacious sidewalks were routinely constructed in European capitals, and were associated with urban sophistication.
Sidewalks play an important role in transportation, as they provide a safe path for people to walk along that is separated from the motorized traffic.
In suburban areas, sidewalks helps to provide equal access to people who cannot drive, notably children, the elderly and the economically disadvantaged. Sidewalks also play an important role in accommodating people that, while perfectly able to drive, may choose not to depending on the length and type of trip they are undertaking - such as a walk to a local shop, a walk for recreation or physical exercise, or taking a pet (such as a dog) for a walk.
In urban areas, such as a downtown district, sidewalks are heavily used as the densely built environment prevents each destination from providing their own parking.
Sidewalks may have a small effect on reducing vehicle miles traveled and carbon dioxide emissions. A study of sidewalk and transit investments in Seattle neighborhoods found vehicle travel reductions of 6 to 8% and CO2 emission reductions of 1.3 to 2.2% 
Research commissioned for the Florida Department of Transportation, published in 2005, found that, in Florida, the Crash Reduction Factor (used to estimate the expected reduction of crashes during a given period) resulting from the installation of sidewalks averaged 74%. Research at the University of North Carolina for the U.S. Department of Transportation found that the presence or absence of a sidewalk and the speed limit are significant factors in the likelihood of a vehicle/pedestrian crash. Sidewalk presence had a risk ratio of 0.118, which means that the likelihood of a crash on a road with a paved sidewalk was 88.2 percent lower than one without a sidewalk. “This should not be interpreted to mean that installing sidewalks would necessarily reduce the likelihood of pedestrian/motor vehicle crashes by 88.2 percent in all situations. However, the presence of a sidewalk clearly has a strong beneficial effect of reducing the risk of a ‘walking along roadway’ pedestrian/motor vehicle crash.” The study does not count crashes that happen when walking across a roadway. The speed limit risk ratio was 1.116, which means that a 16.1-km/h (10-mi/h) increase in the limit yields a factor of (1.116)10 or 3.
The presence or absence of sidewalks was one of three factors that were found to encourage drivers to choose lower, safer speeds.
On the other hand, the implementation of schemes which involve the removal of sidewalks, such as shared space schemes, are reported to deliver a dramatic drop in crashes and congestion too, which indicates that a number of other factors, such as the local speed environment, also play an important role in whether sidewalks are necessarily the best local solution for pedestrian safety.
Riding bicycles on sidewalks is discouraged since it is more dangerous than riding in the street. Some jurisdictions prohibit sidewalk riding except for children. In addition to the risk of cyclist/pedestrian collisions, cyclists face increase risks from collisions with motor vehicles at street crossings and driveways. Riding in the direction opposite to traffic in the adjacent lane is especially risky.
Since residents of neighborhoods with sidewalks are more likely to walk, they tend to have lower rates of cardiovascular disease, obesity, and other health issues related to sedentary lifestyles. Also, children who walk to school have been shown to have better concentration.
Contemporary sidewalks are most often made of concrete in the United States and Canada, while tarmac, asphalt, brick, stone, slab and (increasingly) rubber are more common in Europe. Different materials are more or less friendly environmentally: pumice-based trass, for example, when used as an extender is less energy-intensive than Portland cement concrete or petroleum-based materials such as asphalt or tar-penetration macadam). Multi-use paths alongside roads are sometimes made of materials that are softer than concrete, such as asphalt.
In the 19th century and early 20th century, sidewalks of wood were common in some North American locations. They may still be found at historic beach locations and in conservation areas to protect the land beneath and around, called boardwalks.
In the United States and Canada, the most common type of sidewalk consists of a poured concrete ribbons, examples of which from as early as the 1860s can be found in good repair in San Francisco, and stamped with the name of the contractor and date of installation. When quantities of Portland cement were first imported to the United States in the 1880s, its principal use was in the construction of sidewalks. Today, most sidewalk ribbons are constructed with cross-lying strain relief grooves placed at regular intervals typically 5 feet (1.5 m) apart. This partitioning, an improvement over the continuous slab, was patented in 1924 by Arthur Wesley Hall and William Alexander McVay who wished to minimize damage to the concrete from the effects of tectonic and temperature fluctuations, both of which can crack longer segments. The technique is not perfect, as freeze-thaw cycles (in cold-weather regions) and tree root growth can eventually result in damage which requires repair.
Brick sidewalks are found in some urban areas, usually for aesthetic purposes. Brick sidewalk construction usually involves the usage of a mechanical vibrator to lock the bricks in place after they have been laid (and/or to prepare the soil before laying). Although this might also be done by other tools (as regular hammers and heavy rolls), a vibrator is often used to speed up the process.
In the United Kingdom, Australia and France suburban pavements are most commonly constructed of tarmac, which is however not environmentally friendlier. In urban or inner-city areas pavements are most commonly constructed of slabs, stone, or brick depending upon the surrounding street architecture and furniture.
Stone slabs called flagstones or flags are sometimes used where an attractive appearance is required, as in historic town centres. In other places, pre-cast concrete slabs (called paving slabs or, less correctly, paving stones) are used. These may be coloured or textured to resemble stone.
A sidewalk with street trees in Oak Park, Illinois, USA
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