Personal rapid transit


Personal rapid transit, also referred to as podcars or guided/railed taxis, is a public transport mode featuring a network of specially built guideways on which ride small automated vehicles that carry few passengers per vehicle. PRT is a type of automated guideway transit, a class of system which also includes larger vehicles all the way to small subway systems. In terms of routing, it tends towards personal public transport systems.
PRT vehicles are sized for individual or small group travel, typically carrying no more than three to six passengers per vehicle. Guideways are arranged in a network topology, with all stations located on sidings, and with frequent merge/diverge points. This allows for nonstop, point-to-point travel, bypassing all intermediate stations. The point-to-point service has been compared to a taxi or a horizontal lift.
Numerous PRT systems have been proposed but most have not been implemented., only a handful of PRT systems are operational: Morgantown Personal Rapid Transit, in Morgantown, West Virginia, has been in continuous operation since 1975. Since 2010 a 10-vehicle 2getthere system has operated at Masdar City, UAE, and since 2011 a 21-vehicle Ultra PRT system has run at London Heathrow Airport. A 40-vehicle Vectus system with in-line stations officially opened in Suncheon, South Korea, in April 2014. A PRT system connecting the terminals and parking has been built at the new Chengdu Tianfu International Airport, which opened in 2021.

Overview

Most mass transit systems move people in groups over scheduled routes. This has inherent inefficiencies. For passengers, time is wasted by waiting for the next vehicle to arrive, indirect routes to their destination, stopping for passengers with other destinations, and often confusing or inconsistent schedules. Slowing and accelerating large weights can undermine public transport's benefit to the environment while slowing other traffic.
Personal rapid transit systems attempt to eliminate these wastes by moving small groups nonstop in automated vehicles on fixed tracks. Passengers can ideally board a pod immediately upon arriving at a station, and can – with a sufficiently extensive network of tracks – take relatively direct routes to their destination without stops.
The low weight of PRT's small vehicles allows smaller guideways and support structures than mass transit systems like light rail. The smaller structures translate into lower construction costs, smaller easements, and less visually obtrusive infrastructure.
As it stands, a citywide deployment with many lines and closely spaced stations, as envisioned by proponents, has yet to be constructed. Past projects have failed because of financing, cost overruns, regulatory conflicts, political issues, misapplied technology, and flaws in design, engineering or review.
However, the theory remains active. For example, from 2002 to 2005, the EDICT project, sponsored by the European Union, conducted a study on the feasibility of PRT in four European cities. The study involved 12 research organizations, and concluded that PRT:
  • would provide future cities "a highly accessible, user-responsive, environmentally friendly transport system which offers a sustainable and economic solution."
  • could "cover its operating costs, and provide a return which could pay for most, if not all, of its capital costs."
  • would provide "a level of service which is superior to that available from conventional public transport."
  • would be "well received by the public, both public transport and car users."
The report also concluded that, despite these advantages, public authorities will not commit to building PRT because of the risks associated with being the first public implementation.
Similar to cars / automobiles
  • Vehicles are small—typically two to six passengers
  • Vehicles are individually hired, like taxis, and shared only with the passengers of one's choosing
  • Vehicles travel along a network of guideways, much like a network of streets. Travel is point-to-point, with no intermediate stops or transfers
  • Potential for on-demand, around-the-clock availability
  • Stops are designed to be off the main guideway, allowing through traffic to bypass stations unimpeded
Similar to trams, buses, and monorails
  • A public amenity, shared by multiple users
  • Reduced local pollution
  • Passengers embark and disembark at discrete stations, analogous to bus stops or taxi stands
    • Similar to automated people movers
  • Fully automated, including vehicle control, routing, and collection of fares
  • Usually above the street—typically elevated—reducing land usage and congestion
    • Distinct features
  • Vehicle movements may be coordinated, unlike the autonomous human control of cars and bikes
  • Small vehicle size allows infrastructure to be smaller than other transit modes
  • Automated vehicles can travel close together. Possibilities include dynamically combined "trains" of vehicles, separated by a few inches, to reduce drag and increase speed, energy efficiency and passenger density
    • The PRT acronym was introduced formally in 1978 by J. Edward Anderson. The Advanced Transit Association, a group which advocates the use of technological solutions to transit problems, compiled a definition in 1988 that can be seen here.

    List of operational automated transit networks (ATN) systems

    Currently, five advanced transit networks systems are operational, and several more are in the planning stage.
    SystemManufacturerTypeLocationsLengthNotes
    Morgantown PRTBoeingGRT
    convert|13.2|km|mi|1|abbr=on|sortable=on

    List of ATN suppliers

    The following list summarizes several well-known automated transit networks suppliers as of 2014, with subsequent amendments.

    Origins

    Modern PRT concepts began around 1953 when Donn Fichter, a city transportation planner, began research on PRT and alternative transportation methods. In 1964, Fichter published a book which proposed an automated public transit system for areas of medium to low population density. One of the key points made in the book was Fichter's belief that people would not leave their cars in favor of public transit unless the system offered flexibility and end-to-end transit times that were much better than existing systems - flexibility and performance he felt only a PRT system could provide. Several other urban and transit planners also wrote on the topic and some early experimentation followed, but PRT remained relatively unknown.
    Around the same time, Edward Haltom was studying monorail systems. Haltom noticed that the time to start and stop a conventional large monorail train, like those of the Wuppertal Schwebebahn, meant that a single line could only support between 20 and 40 vehicles an hour. In order to get reasonable passenger movements on such a system, the trains had to be large enough to carry hundreds of passengers. This, in turn, demanded large guideways that could support the weight of these large vehicles, driving up capital costs to the point where he considered them unattractive.
    Haltom turned his attention to developing a system that could operate with shorter timings, thereby allowing the individual cars to be smaller while preserving the same overall route capacity. Smaller cars would mean less weight at any given point, which meant smaller and less expensive guideways. To eliminate the backup at stations, the system used "offline" stations that allowed the mainline traffic to bypass the stopped vehicles. He designed the Monocab system using six-passenger cars suspended on wheels from an overhead guideway. Like most suspended systems, it suffered from the problem of difficult switching arrangements. Since the car rode on a rail, switching from one path to another required the rail to be moved, a slow process that limited the possible headways.

    UMTA is formed

    By the late 1950s the problems with urban sprawl were becoming evident in the United States. When cities improved roads and the transit times were lowered, suburbs developed at ever increasing distances from the city cores, and people moved out of the downtown areas. Lacking pollution control systems, the rapid rise in car ownership and the longer trips to and from work were causing significant air quality problems. Additionally, movement to the suburbs led to a flight of capital from the downtown areas, one cause of the rapid urban decay seen in the US.
    Mass transit systems were one way to combat these problems. Yet during this period, the federal government was feeding the problems by funding the development of the Interstate Highway System, while at the same time funding for mass transit was being rapidly scaled back. Public transit ridership in most cities plummeted.
    In 1962, President John F. Kennedy charged Congress with the task of addressing these problems. These plans came to fruition in 1964, when President Lyndon B. Johnson signed the Urban Mass Transportation Act of 1964 into law, thereby forming the Urban Mass Transportation Administration. UMTA was set up to fund mass transit developments in the same fashion that the earlier Federal Aid Highway Act of 1956 had helped create the Interstate Highways. That is, UMTA would help cover the capital costs of building out new infrastructure.

    PRT research starts

    However, planners who were aware of the PRT concept were worried that building more systems based on existing technologies would not help the problem, as Fitcher had earlier noted. Proponents suggested that systems would have to offer the flexibility of a car:

    The reason for the sad state of public transit is a very basic one – the transit systems just do not offer a service which will attract people away from their automobiles. Consequently, their patronage comes very largely from those who cannot drive, either because they are too young, too old, or because they are too poor to own and operate an automobile. Look at it from the standpoint of a commuter who lives in a suburb and is trying to get to work in the central business district. If he is going to go by transit, a typical scenario might be the following: he must first walk to the closest bus stop, let us say a five or ten minute walk, and then he may have to wait up to another ten minutes, possibly in inclement weather, for the bus to arrive. When it arrives, he may have to stand unless he is lucky enough to find a seat. The bus will be caught up in street congestion and move slowly, and it will make many stops completely unrelated to his trip objective. The bus may then let him off at a terminal to a suburban train. Again he must wait, and, after boarding the train, again experience a number of stops on the way to the CBD, and possibly again he may have to stand in the aisle. He will get off at the station most convenient to his destination and possibly have to transfer again onto a distribution system. It is no wonder that in those cities where ample inexpensive parking is available, most of those who can drive do drive.

    In 1966, the United States Department of Housing and Urban Development was asked to "undertake a project to study... new systems of urban transportation that will carry people and goods... speedily, safely, without polluting the air, and in a manner that will contribute to sound city planning." The resulting report was published in 1968 and proposed the development of PRT, as well as other systems such as dial-a-bus and high-speed interurban links.
    In the late 1960s, the Aerospace Corporation, an independent non-profit corporation set up by the US Congress, spent substantial time and money on PRT, and performed much of the early theoretical and systems analysis. However, this corporation is not allowed to sell to non-federal government customers. In 1969, members of the study team published the first widely publicized description of PRT in Scientific American.
    In 1978 the team also published a book. These publications sparked off a sort of "transit race" in the same sort of fashion as the space race, with countries around the world rushing to join what appeared to be a future market of immense size.
    The oil crisis of 1973 made vehicle fuels more expensive, which naturally interested people in alternative transportation.