Footbridge
A footbridge (also a pedestrian bridge, pedestrian overpass, or pedestrian overcrossing) is a bridge designed solely for pedestrians. While the primary meaning for a bridge is a structure which links "two points at a height above the ground", a footbridge can also be a lower structure, such as a boardwalk, that enables pedestrians to cross wet, fragile, or marshy land. Bridges range from stepping stones–possibly the earliest man-made structure to "bridge" water–to elaborate steel structures. Another early bridge would have been simply a fallen tree. In some cases a footbridge can be both functional and artistic . For rural communities in the developing world, a footbridge may be a community's only access to medical clinics, schools, businesses and markets. Simple suspension bridge designs have been developed to be sustainable and easily constructed in such areas using only local materials and labor. An enclosed footbridge between two buildings is sometimes known as a skyway. Bridges providing for both pedestrians and cyclists are often referred to as greenbridges and form an important part of a sustainable transport system. Footbridges are often situated to allow pedestrians to cross water or railways in areas where there are no nearby roads . They are also located across roads to let pedestrians cross safely without slowing traffic. The latter is a type of pedestrian separation structure, examples of which are particularly found near schools. Early history. The simplest type of a bridge is stepping stones, so this may have been one of the earliest types of footbridge. Neolithic people also built a form of a boardwalk across marshes, of which the Sweet Track, and the Post Track are examples from England, that are around 6000 years old. Undoubtedly ancient peoples would also have used log bridges; that is a timber bridge that fall  naturally or are intentionally felled or placed across streams. Some of the first man-made bridges with significant span were probably intentionally felled trees. Among the oldest timber bridges is the Holzbrücke Rapperswil-Hurden crossing upper Lake Zürich in Switzerland; the prehistoric timber piles discovered to the west of the Seedamm date back to 1523 B.C. The first wooden footbridge led across Lake Zürich, followed by several reconstructions at least until the late 2nd century AD, when the Roman Empire built a wooden bridge. Between 1358 and 1360, Rudolf IV, Duke of Austria, built a 'new' wooden bridge across the  lake that has been used to 1878 – measuring approximately in length and wide. On April 6, 2001, the reconstructed wooden footbridge was opened, being the longest wooden bridge in Switzerland. A clapper bridge is an ancient form of bridge found on the moors of Devon (Dartmoor and Exmoor) and in other upland areas of the United Kingdom including Snowdonia and Anglesey, Cumbria, Yorkshire and Lancashire. It is formed by large flat slabs of stone, often granite or schist, supported on stone piers (across rivers), or resting on the banks of streams. Although often credited with prehistoric origin, most were erected  in medieval times, and some in later centuries. A famous example is found in the village of Postbridge. First recorded in the 14th century, the bridge is believed to have been originally built in the 13th century to enable pack horses to cross the river. Nowadays clapper bridges are only used as footbridges. The Kapellbrücke is a footbridge crossing the River Reuss in the city of Lucerne in Switzerland. It is the oldest wooden covered bridge in Europe, and one of Switzerland's main tourist attractions. The bridge was originally built 1365 as part of Lucerne's fortifications. An early  example of a skyway is the Vasari Corridor, an elevated, enclosed passageway in Florence, central Italy, which connects the Palazzo Vecchio with the Palazzo Pitti. Beginning on the south side of the Palazzo Vecchio, it then joins the Uffizi Gallery and leaves on its south side, crossing the Lungarno dei Archibusieri and then following the north bank of the River Arno until it crosses the river at Ponte Vecchio. It was built in five months by order of Duke Cosimo I de' Medici in 1565, to the design of Giorgio Vasari. Bank Bridge is a famous 25 metre long pedestrian  bridge crossing the Griboedov Canal in Saint Petersburg, Russia. Like other bridges across the canal, the existing structure dates from 1826. The special popularity of the bridge was gained through angular sculptures of four winged lions crowning the abutments. They were designed by sculptor Pavel Sokolov (1764-1835), who also contributed lions for Bridge of Lions. Design. Design of footbridges normally follows the same principles as for other bridges. However, because they are normally significantly lighter than vehicular bridges, they are more vulnerable to vibration and therefore dynamics effects are often given more attention in design. International attention has been  drawn to this issue in recent years by problems on the Pont de Solférino in Paris and the Millennium Bridge in London. To ensure footbridges are accessible to disabled and other mobility-impaired people, careful consideration is nowadays also given to provision of access lifts or ramps, as required by relevant legislation (e.g. Disability Discrimination Act 1995 in the UK). Some old bridges in Venice are now equipped with a stairlift so that residents with a disability can cross them. Types. Types of footbridges include: The residential-scale footbridges all span a short distance and can be used for a  broad range of applications. Complicated engineering is not needed and the footbridges are built with readily available materials and basic tools. Different types of design footbridges include: Footbridges can also be built in the same ways as road or rail bridges; particularly suspension bridges and beam bridges. Some former road bridges have had their traffic diverted to alternative crossings and have become pedestrian bridges; examples in the UK include The Iron Bridge at Ironbridge, Shropshire, the Old Bridge at Pontypridd and Windsor Bridge at Windsor, Berkshire. Most footbridges are equipped with guard rails to reduce the risk of pedestrians falling . Where they pass over busy roads or railways, they may also include a fence or other such barrier to prevent pedestrians from jumping, or throwing projectiles onto the traffic below. Railways. It was originally usual for passengers to cross from one railway platform to another by stepping over the tracks, but from the mid-19th century onwards safety demanded the provision of a footbridge (or underpass) at busier places. However, in some quieter areas, crossing the line by walking over the tracks is possible. Catwalk. Narrow footbridges or walkways to allow workers access to parts of a structure otherwise difficult to  reach are referred as catwalks or cat walks. Such catwalks are located above a stage (theater catwalk) in a theater, between parts of a building, along the side of a bridge, on the inside of a tunnel, on the outside of any large storage tank in a refinery or elsewhere, etc. The walkway on the outside (top) of a railroad cars such as boxcars, before air brakes came into use, or on top of some covered hopper cars is also called a catwalk. With the exception of those on top of railroad cars, catwalks are equipped with railings or handrails . In developing countries. Since the early 1980s, several charities have developed standardized footbridge designs that are sustainable for use in developing countries. The first charity to develop such designs was Helvetas, located in Zurich, Switzerland. Designs that can be sustainably and efficiently used in developing countries are typically made available to the public gratis. Long footbridges. The record for the longest footbridge in the world was claimed by then New York State Governor David Paterson in an Oct. 3, 2009 Poughkeepsie Journal article about The Walkway Poughkeepsie Bridge across the Hudson River at Poughkeepsie, New York. On July 22, 2017 , the Champlain Bridge Ice Structure (, a bridge built for bicycles and foot traffic only to parallel the Champlain Bridge from Brossard, Quebec west to Nun's Island (L'ile Des Soeurs) & the Island of Montreal, was measured by a calibrated device as being 7,512 feet (2,292 meters) long or 1.4227 miles or 2.292km, starting and ending where the treadway rises above the ground and a pedestrian could access the bridge as close as possible to the St Lawrence River. Arouca 516, the longest pedestrian suspension bridge, which spans the River Paiva, Arouca Geopark, Portugal, opened in April 2021. The 516  metres bridge hangs 175 meters above the river. The United Wholesale Mortgage Pedestrian Bridge in Pontiac, Michigan is the longest enclosed pedestrian bridge, completed in October 1, 2021. The 305 metre bridge was part of a $250 million project to UWM’s offices, which converted a former warehouse and utilized shipping containers for offices, corridors, and other spaces. The Walkway Over The Hudson footbridge was originally built for trains, it was recently restored as a pedestrian walkway. The footbridge has a total length of 2,063 meters (6,768 feet). Before it was demolished in 2011, the Hornibrook Bridge which crossed  Bramble Bay in Queensland, Australia was longer than the Poughkeepsie Bridge at 2.684 km (1.7 mi). Advantages. Much rural travel takes place on local footpaths, tracks and village roads. These provide essential access to water, firewood, farm plots and the classified road network. Communities and/or local government are generally responsible for this infrastructure. Disadvantages. Pedestrian overpasses over highways or railroads are expensive, especially when elevators or long ramps for wheelchair users are required. Without elevators or ramps, people with mobility handicaps will not be able to use the structure. People may prefer to walk across a busy road rather than  climb a bridge, and this may be attributed to being in a hurry, perceiving the safety and security of the footbridge to be low, or simply because of feeling tiredness when climbing the stairs. It is recommended that overpasses should only be used where the number of users justify the costs. The operational concept of the footbridge is based on the notion that pedestrians need to walk a longer distance and exert more physical effort so that the traffic flow is not interrupted. This is not in line with the sustainability goals of the transport system promoting active travel such  as walking and cycling. A change of policy to increase safety and walkability could involve transferring that effort of crossing the road to drivers who will need to wait longer so pedestrians can cross the road safely at street level. Narrow, enclosed structures can result in perceptions of low personal security among users. Wider structures and good lighting can help reduce this.