Personal rapid transit (PRT), also called
personal automated transport (PAT) or
podcar, is a
public transportPublic transport comprises passenger transportation services which are available for use by the general public, as opposed to modes for private use such as automobiles or vehicles for hire.Public transport services are usually funded by fares charged to each passenger, with varying levels of subsidy...
ation concept that offers on-demand, non-stop transportation, using small, independent vehicles on a network of specially-built guideways. Several different designs have been proposed, and in October 2008, construction of the guideway of a pilot project at
London Heathrow AirportLondon Heathrow Airport or Heathrow , located in the London Borough of Hillingdon, is the world's busiest airport in terms of international passenger traffic. It is the world's second busiest airport in total passenger traffic. It is also the largest and busiest airport in the United Kingdom...
,
United KingdomThe United Kingdom of Great Britain and Northern Ireland is a sovereign state located off the northwestern coast of continental Europe. It is an island country, spanning an archipelago including Great Britain, the northeastern part of Ireland, and many small islands...
based on
ULTraULTra is a personal rapid transit system from Advanced Transport Systems Ltd, a company based in Cardiff, Wales. The system was conceived by Martin Lowson and his design team, Lowson having put £10 million into the project...
was completed.
With completion of the guideway, fit out of the stations and track can begin. The operators now expect the system to open to airport users in late Spring 2010.
A quasi-PRT network, the
Morgantown Personal Rapid TransitThe Morgantown Personal Rapid Transit system is a one-of-a-kind people mover system in Morgantown, West Virginia, United States...
of
West Virginia UniversityWest Virginia University is a public research university in Morgantown, West Virginia, USA. Other campuses include: West Virginia University at Parkersburg in Parkersburg; West Virginia University Institute of Technology in Montgomery; Potomac State College of West Virginia University in Keyser;...
in the
United StatesThe United States of America is a federal constitutional republic comprising fifty states and a federal district...
, has been operational since 1975.
Overview
Most mass transit systems move people in groups over scheduled routes, which have certain inherent inefficiencies. For passengers, time is wasted by waiting for the next arrival, 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 theoretically 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.
Perhaps most importantly, PRT systems offer a more viable long term alternative to cars because they too offer privacy and the ability to choose one's own schedule. Such a system may in fact allow for quicker transportation than cars in some contexts, considering that automated vehicles avoid slowing unnecessarily. The PRT system can, furthermore, be extended to support the transport of freight and other deliveries which, if city-wide, would eliminate the need for cars and mass transit systems altogether.
The low weight of PRT's small vehicles allows smaller guideways and support structures than other mass transit systems like light rail. The smaller structures translate into lower construction cost, smaller easements, and less visually obtrusive infrastructure.
As it stands, however, such a system remains more of a potential than a proven reality. A city-wide deployment with many lines and closely-spaced stations, as envisaged by proponents, has yet to be constructed. Past projects have failed because of financing; cost overruns; regulatory conflicts; political issues; technological limitations; and flaws in design, engineering or review.
However, the theory remains persuasive. For example, from 2002–2005, 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, environmental 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.
Comparison of Personal Rapid Transit with existing transport systems
Similar to automobileAn automobile, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
s |
- 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 tramA tram, tramcar, trolley, trolleycar, or streetcar is a railborne vehicle, of lighter weight and construction than a conventional train, designed for the transport of passengers within, close to, or between villages, towns and/or cities, on tracks running primarily on streets...
s, busA bus is a road vehicle designed to carry passengers. A bus seats a maximum of 8 to 300 passengers...
es, and monorailA monorail is a rail-based transportation system based on a single rail, which acts as its sole support and its guideway. The term is also used variously to describe the beam of the system, or the vehicles traveling on such a beam or track. The term originates from the contraction of the words mono...
s |
A public amenity (although not necessarily publicly owned), shared by multiple users
Reduced local pollution (electric powered)
Passengers embark and disembark at discrete stations, analogous to bus stop A bus stop is a designated place where a public transport bus stops for the purpose of allowing passengers to board or leave a bus.- Type :There are three main kinds of stops:* Scheduled stop: The bus uses the stop irrespective of demand...
s or taxi standA taxicab stand is a queue area on a street or on private property where taxicabs line up to wait for passengers.- How stands work :...
s |
Similar to automated people moverA people mover or automated people mover is a fully automated, grade-separated mass transit system.-Terminology:The term is generally used only to describe systems serving relatively small areas such as airports, downtown districts or theme parks, but is sometimes applied to considerably more...
s |
Fully automated, including vehicle control, routing, and collection of fares
Usually off-grade—typically elevated—reducing land usage and congestion |
| Distinct features |
Vehicle movements may be coordinated, unlike the autonomous human control of automobiles 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 dragIn fluid dynamics, drag refers to forces that oppose the relative motion of an object through a fluid . Drag forces act in a direction opposite to the oncoming flow velocity...
and increase speed, energy efficiency and passenger density |
The PRT acronym was introduced formally in 1978 by
J. Edward AndersonJ. Edward Anderson , is an American engineer and proponent of personal rapid transit.-Career:Anderson was born in China in the 1920s. His family returned to the United States in the 1930s. He obtained a BS from Iowa State University and a masters from the University of Minnesota - both in the field...
. The Advanced Transit Association (ATRA), a group which advocates the use of technological solutions to transit problems, compiled a definition in 1988 that can be seen
here.
PRT networks
Currently, one quasi-PRT network is operational, another full-PRT network is under construction, and several more are in the planning stage.
| Location |
Status |
System |
Date |
Guideway |
Stations / Vehicles |
Notes |
Morgantown, West VirginiaMorgantown is a city in and the county seat of Monongalia County, West Virginia, United States, on the banks of the Monongahela River. Part of the Pittsburgh Tri-State region, Morgantown is the largest city in North-Central West Virginia, and is the principal city of the Morgantown, West Virginia...
, USA |
Operational |
WVU PRTThe Morgantown Personal Rapid Transit system is a one-of-a-kind people mover system in Morgantown, West Virginia, United States...
|
1975 |
km |
5 / 73 |
Up to 20 passengers per vehicle, some rides not point-to-point during low usage periods |
London Heathrow AirportLondon Heathrow Airport or Heathrow , located in the London Borough of Hillingdon, is the world's busiest airport in terms of international passenger traffic. It is the world's second busiest airport in total passenger traffic. It is also the largest and busiest airport in the United Kingdom...
, UK |
Construction Completed, Under Testing |
ULTra ULTra is a personal rapid transit system from Advanced Transport Systems Ltd, a company based in Cardiff, Wales. The system was conceived by Martin Lowson and his design team, Lowson having put £10 million into the project...
|
2009 |
km |
3 / 18 |
Will be the world's first true commercial PRT system, initially connecting Terminal 5 with a long-term car park. If successful, BAA plans to extend it throughout the airport. |
Masdar CityMasdar City is a planned city in Abu Dhabi, in the United Arab Emirates. It is being built by the Abu Dhabi Future Energy Company, a subsidiary of Mubadala Development Company, with the majority of seed capital provided by the government of Abu Dhabi...
, Abu Dhabi, UAE |
Planned |
2getthere |
2011 |
? |
83 / 2500 |
Automobiles will be banned, the only powered transport will be PRT and intercity light rail |
| Daventry Daventry is a market town in Northamptonshire, England, with a population of 22,367 . The town is also the administrative centre of the larger Daventry district, which has a population of 71,838. The town is 124 km north-northwest of London, 22.4 km west of Northampton and 16.4 km...
, Northamptonshire, UK |
Planned |
T.B.D. |
2012 |
km |
5 / 25 |
|
| Capital City, Dubai, UAE |
Proposed |
T.B.D. |
|
|
|
|
| Lulu Island, Abu Dhabi, UAE |
Proposed |
T.B.D. |
|
|
|
|
Santa Cruz, CaliforniaSanta Cruz is the county seat and largest city of Santa Cruz County, California in the United States of America. As of the 2006 census estimate, Santa Cruz had a total population of 54,778, up 0.3% from the 2000 Census...
, USA |
Proposed |
T.B.D. |
|
|
|
|
| Bawadi Bawadi is a project announced by the government of Dubai, United Arab Emirates on 1 May 2006. The developer is Tatweer, a subsidiary of Dubai Holding....
, Dubai, UAE |
Proposed |
T.B.D. |
|
|
|
The overall Bawadi development is 139 million sq. meters and 10 km in length |
PRT designs
The following table summarizes several well-known PRT designs.
| System |
Location |
Active? |
Status |
Seating Capacity
(per vehicle) |
Guideway |
Suspended/
Supported |
Propulsion |
Morgantown PRTThe Morgantown Personal Rapid Transit system is a one-of-a-kind people mover system in Morgantown, West Virginia, United States...
(BoeingThe Boeing Company is a major aerospace and defense corporation, founded by William E. Boeing in Seattle, Washington. Boeing has expanded over the years, merging with McDonnell Douglas in 1997. Its international headquarters has been in Chicago, Illinois, since 2001...
) |
West Virginia |
Yes |
In Service |
8 seated plus 12 standing |
concrete |
supported |
rotary motors |
| ULTra ULTra is a personal rapid transit system from Advanced Transport Systems Ltd, a company based in Cardiff, Wales. The system was conceived by Martin Lowson and his design team, Lowson having put £10 million into the project...
(ATS Ltd) |
UK |
Yes |
Construction of pilot completed |
4 |
concrete |
supported |
rotary motors |
| 2getthere PRT |
the Netherlands |
Yes |
10 vehicles produced |
6 |
concrete |
supported |
rotary motors |
| Vectus PRT (POSCO The Pohang Iron and Steel Company, or POSCO , based in Pohang, South Korea, is the world's second largest steel maker by market value....
) |
Korea |
Yes |
Full Prototype |
4 |
steel |
supported |
linear motors |
| Cabinentaxi Cabinentaxi was a German urban transit development project, undertaken by the joint venture of Mannesmann Demag and Messerschmitt-Bölkow-Blohm under a program of the German Bundesministerium für Bildung und Forschung...
|
Germany |
US Company Active in Private Sector |
Completed system: 1980's approval for federal transit programs in Germany and US |
3,12,18 |
steel |
both |
linear motors |
| CVS |
Japan |
No |
Full Prototype |
4 |
steel |
supported |
rotary motors |
PRT2000 (RaytheonRaytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in defense systems and defense and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...
) |
USA |
No |
Full Prototype |
4 |
steel |
supported |
rotary motors |
| Skyweb Express (Taxi2000) |
Minnesota |
Yes |
Partial prototype |
3 |
steel |
supported |
linear motors |
| MISTER MISTER is a personal rapid transit system developed in Poland. It belongs to the group of PRT systems using a carriage suspended beneath a rail, mounted approximately 6 meters above the ground...
|
Poland |
Yes |
Partial Prototype |
5 |
steel |
suspended |
rotary motors |
| JPods |
USA |
Yes |
Mockup |
4 |
steel |
suspended |
rotary motors |
| SkyTaxi |
Russia |
Yes |
Concept |
1,2,4 |
steel |
supported |
rotary motors |
Morgantown PRT is known as a quasi-PRT system, because it lacks some PRT features such as 100% on-demand service.
History
Some of the key concepts of PRT have been toyed with since the 1890s, but modern PRT really 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. In 1966, the
United States Department of Housing and Urban DevelopmentThe United States Department of Housing and Urban Development, also known by as HUD, is a Cabinet department in the Executive branch of the United States federal government...
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 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 AmericanScientific American is a popular science magazine published since August 28, 1845, which according to the magazine makes it the oldest continuously published magazine in the United States...
.
In 1978 the team also published a book.
In 1967, aerospace giant
MatraMécanique Avion TRAction or Matra was a French company covering a wide range of activities mainly related to automobile, bicycles, aeronautics and weaponry which from 1994 was a subsidiary of Lagardère Group and which now operates under that name....
started the Aramis project in
ParisParis is the capital of France and the country's most populous city. It is situated on the river Seine, in northern France, at the heart of the Île-de-France region...
. After spending about 500 million francs, the project was canceled when it failed its qualification trials in November 1987. The designers tried to make Aramis work like a "virtual train," but control software issues caused cars to bump unacceptably. The project ultimately failed.
The oil crisis of 1973 made vehicle fuels more expensive, stimulating PRT development.
Between 1970 and 1978, Japan operated a project called
Computer-controlled Vehicle System (CVS). In a full-scale test facility, 84 vehicles operated at speeds up to on a guideway; one-second
headwayHeadway is a measurement of the distance between vehicles in a transit system. The precise definition varies depending on the application, but it is most commonly measured as the distance from the tip of one vehicle to the tip of the next one behind it, expressed as the time it will take for the...
s were achieved during tests. Another version of CVS was in public operation for six months from 1975–1976. This system had 12 single-mode vehicles and four dual-mode vehicles on a track with five stations. This version carried over 800,000 passengers. CVS was cancelled when Japan's Ministry of Land, Infrastructure and Transport declared it unsafe under existing rail safety regulations, specifically in respect of braking and headway distances.
On March 23, 1973, U.S. Urban Mass Transportation Administration (UMTA) administrator Frank Herringer testified before Congress: "A DOT program leading to the development of a short, one-half to one-second headway, high-capacity PRT (HCPRT) system will be initiated in fiscal year 1974." However, this HCPRT program was diverted into a modest technology program. According to PRT supporter
J. Edward AndersonJ. Edward Anderson , is an American engineer and proponent of personal rapid transit.-Career:Anderson was born in China in the 1920s. His family returned to the United States in the 1930s. He obtained a BS from Iowa State University and a masters from the University of Minnesota - both in the field...
, this was "because of heavy lobbying from interests fearful of becoming irrelevant if a genuine PRT program became visible". From that time forward people interested in HCPRT were unable to obtain UMTA research funding.
In 1975, the
Morgantown Personal Rapid TransitThe Morgantown Personal Rapid Transit system is a one-of-a-kind people mover system in Morgantown, West Virginia, United States...
project was completed. Despite its name and fact that it has five off-line stations that enable non-stop, individually programmed trips that are characteristic of PRT, this is not considered a PRT system by authorities because its vehicles are too heavy and carry too many people, and because some of the time it does not operate in a point-to-point fashion, running instead like an automated people mover from one end of the line to the other. The PRT system is still in continuous operation at
West Virginia UniversityWest Virginia University is a public research university in Morgantown, West Virginia, USA. Other campuses include: West Virginia University at Parkersburg in Parkersburg; West Virginia University Institute of Technology in Montgomery; Potomac State College of West Virginia University in Keyser;...
in
Morgantown, West VirginiaMorgantown is a city in and the county seat of Monongalia County, West Virginia, United States, on the banks of the Monongahela River. Part of the Pittsburgh Tri-State region, Morgantown is the largest city in North-Central West Virginia, and is the principal city of the Morgantown, West Virginia...
with about 15,000 riders per day . It successfully demonstrates automated control, but was not sold to other sites because the heated track has proven too expensive.
From 1969 to 1980, Mannesmann Demag and
MBBMesserschmitt-Bölkow-Blohm was a German aerospace company formed as the result of several mergers in the late 1960s. Among its best-known products was the MBB Bo 105 light twin helicopter...
cooperated to build the
CabinentaxiCabinentaxi was a German urban transit development project, undertaken by the joint venture of Mannesmann Demag and Messerschmitt-Bölkow-Blohm under a program of the German Bundesministerium für Bildung und Forschung...
urban transportation system in Germany. Together the firms formed the Cabintaxi Joint Venture. They created an extensive PRT technology that was considered fully developed by the German Government and its safety authorities. The system was to have been installed in Hamburg, but budget cuts stopped the proposed project before the start of construction. With no other project potentials on the horizon, the joint venture disbanded, and the fully developed PRT technology was never installed. Cabintaxi Corporation, a US based company obtained the technology in 1985, and remains active in the private sector market for transportation systems.
In the 1990s,
RaytheonRaytheon Company is a major American defense contractor and industrial corporation with core manufacturing concentrations in defense systems and defense and commercial electronics. It was previously involved in corporate and special-mission aircraft until early 2007...
invested heavily in a system called PRT2000 that was based on technology developed by
J. Edward AndersonJ. Edward Anderson , is an American engineer and proponent of personal rapid transit.-Career:Anderson was born in China in the 1920s. His family returned to the United States in the 1930s. He obtained a BS from Iowa State University and a masters from the University of Minnesota - both in the field...
at the
University of MinnesotaThe University of Minnesota, Twin Cities is a public research university located in Minneapolis and St. Paul, Minnesota, United States...
. Raytheon failed to install a contracted system in
Rosemont, IllinoisRosemont is a village in Cook County, Illinois, United States located immediately northwest of Chicago. The village was incorporated in 1956, though it had been settled long before that...
, near
ChicagoChicago is the largest city in the U.S. state of Illinois, and with more than 2.8 million people, the 3rd largest city in the United States...
, when estimated costs escalated to US$50 million per mile, allegedly due to design changes that increased the weight and cost of the Raytheon system relative to Anderson's original design. In 2000, rights to the technology reverted to the University of Minnesota, and were subsequently purchased by Taxi2000.
In 2002 2getthere operated 25 4-passenger "CyberCabs" at Holland's 2002
FloriadeFloriade is:*A flower festival held annually in Canberra, Australia. See: Floriade, Canberra*A large flower and gardening exhibition, held every 10 years in The Netherlands. See: Floriade, Netherlands...
horticultural exhibition. These transported passengers along a track spiraling up to the summit of Big Spotters Hill. The track was approximately long (one-way) and featured only two stations. The 6-month operations were mainly intended to research the public acceptance of PRT-like systems. The CyberCab as designed for the exhibition, being very open, is comparable to a
Neighborhood Electric VehicleA Neighborhood Electric Vehicle is a battery electric vehicle falling under United States Department of Transportation classification for low-speed vehicles. The NEV operates by plugging into a standard outlet at home...
, except it steers itself using magnet guidance points embedded in the lane.
Ford Research proposed a
dual-modeA dual-mode vehicle is a vehicle that can run on either a track or roadways. These include both small individual vehicles as well as larger trollies. The benefits of the tracks are: recharge batteries ; guidance; and the ability to run groups of vehicles in tight formation, which greatly increases...
system called PRISM.
It would use public guideways with privately purchased but certified dual-mode vehicles. The vehicles would weigh less than . Most energy use occurs on highways, so small, elevated guideways would
inductively powerA transformer is a device that transfers electrical energy from one circuit to another through inductively coupled conductors—the transformer's coils. A varying current in the first or primary winding creates a varying magnetic flux in the transformer's core, and thus a varying magnetic field...
highway use and recharge batteries for off-guideway use. Central computers could do routing.
In January 2003, the prototype ULTra ("Urban Light Transport") system from Advanced Transport Systems Ltd. in Cardiff, Wales, was certified to carry passengers by the UK Railway Inspectorate on a test track. ULTra was selected in October 2005 by
BAA plcBAA Airports Ltd. is the owner and operator of seven British airports and the operator of several other airports worldwide, making the company one of the largest transport companies in the world...
for London's Heathrow Airport. This system is planned to initially transport passengers from a remote parking lot to the central terminal area. If the initial system is successful, further plans call for expansion throughout the airport and the surrounding region.
In June 2006, a Korean/Swedish consortium, Vectus Ltd, started constructing a test track in Uppsala, Sweden.
This test system was presented at the 2007 PodCar City conference in Uppsala, Sweden.
System design
Among the handful of prototype systems (and the larger number that exist on paper) there is a substantial diversity of design approaches, some of which are controversial.
Vehicle design
Vehicle weight influences the size and cost of a system's guideways, which are in turn a major part of the capital cost of the system. Larger vehicles are more expensive to produce, require larger and more expensive guideways, and use more energy to start and stop. If vehicles are too large, point-to-point routing also becomes less economically feasible. Against this, smaller vehicles have more surface area per passenger (thus have higher total air resistance which dominates the energy cost of keeping vehicles moving at speed) and larger motors are generally more efficient than smaller ones.
The number of riders who will share a vehicle is a key unknown. In the U.S., the average private automobile carries 1.16 persons, and most industrialized countries commonly average below two people; not having to share a vehicle with strangers is a key advantage of private transport. Based on these figures, some have suggested that two passengers per vehicle (such as with UniModal), or even a single passenger per vehicle is optimum. Other designs choose larger vehicles, making it possible to accommodate families with small children, riders with bicycles, and disabled passengers with wheelchairs.
Propulsion
All current designs are powered by
electricityElectricity is a general term that encompasses a variety of phenomena resulting from the presence and flow of electric charge...
. In order to reduce vehicle weight, power is generally transmitted via lineside conductors rather than using on-board batteries. According to the designer of Skyweb/Taxi2000,
J. Edward AndersonJ. Edward Anderson , is an American engineer and proponent of personal rapid transit.-Career:Anderson was born in China in the 1920s. His family returned to the United States in the 1930s. He obtained a BS from Iowa State University and a masters from the University of Minnesota - both in the field...
, the lightest system is a linear induction motor (LIM) on the car, with a stationary conductive rail for both propulsion and braking. LIMs are used in a small number of rapid transit applications, but most designs use rotary motors.
Switching
Most designers avoid
track switchingA railroad switch, turnout or [set of] points is a mechanical installation enabling railway trains to be guided from one track to another at a railway junction....
, instead advocating vehicle-mounted switches or conventional steering. Those designers say that vehicle-switching simplifies the guideway, makes junctions less visually obtrusive and reduces the impact of malfunctions, because a failed switch on one vehicle is less likely to affect other vehicles. Other designers point out that track-switching simplifies the vehicles, reducing the number of small moving parts in each car. Track-switching replaces in-vehicle mechanisms with larger track-moving components, that can be designed for durability with little regard for weight or size.
Track switching also greatly increases headway distance. A vehicle must wait for the previous vehicle to clear the track, for the track to switch and for the switch to be verified. If the track switching is faulty, vehicles must be able to stop before reaching the switch, and all vehicles approaching the failed junction would be affected.
Mechanical vehicle switching minimizes inter-vehicle spacing or headway distance, but it also increases the minimum distances between consecutive junctions. A mechanically switching vehicle, maneuvering between two immediately adjacent junctions requiring different switch settings, cannot proceed immediately from one junction to the next. The vehicle must wait after clearing the first junction for the in-vehicle switches to adopt a new switch position, and then wait for the in-vehicle switch's locking mechanism to be verified. If the vehicle switching is faulty, that vehicle must be able to stop before reaching the next switch, and all vehicles approaching the failed vehicle would be affected.
Infrastructure design
Guideways
There is some debate over the best type of guideway. Among the proposals are beams similar to monorails, bridge-like trusses supporting internal tracks, and cables embedded in a roadway. Most designs put the vehicle on top of the track, which reduces visual intrusion and cost as well as facilitating ground-level installation. An overhead track is necessarily higher, but may also be narrower. Most designs use the guideway to distribute power and data communications, including to the vehicles. The
Morgantown PRTThe Morgantown Personal Rapid Transit system is a one-of-a-kind people mover system in Morgantown, West Virginia, United States...
failed its cost targets because of its steam-heated track, so most proposals plan to resist snow and ice in ways that should be less expensive.
Stations
Proposals usually have stations close together, and located on side tracks so that through traffic can bypass vehicles picking up or dropping off passengers. Each station might have multiple berths, with perhaps one-third of the vehicles in a system being stored at stations waiting for passengers. Stations are envisioned to be minimalistic, and not include facilities such as rest rooms. For elevated stations, an elevator may be required for accessibility.
Some designs have included substantial extra expense for the track needed to decelerate to and accelerate from stations. In at least one system, Aramis, this nearly doubled the width and cost of the required right-of-way and caused the nonstop passenger delivery concept to be abandoned. Other designs have schemes to reduce this cost, for example merging vertically to reduce the footprint.
Headway distance
Spacing of vehicles on the guideway influences the maximum passenger capacity of a track, so designers prefer smaller
headwayHeadway is a measurement of the distance between vehicles in a transit system. The precise definition varies depending on the application, but it is most commonly measured as the distance from the tip of one vehicle to the tip of the next one behind it, expressed as the time it will take for the...
distances. Computerized control theoretically permits closer spacing than the two-second headways recommended for cars at speed, since multiple vehicles can be braked simultaneously. There are also prototypes for automatic guidance of private cars based on similar principles.
Very short headways are controversial. The UK Railway Inspectorate has evaluated the ULTra design and is willing to accept one-second headways, pending successful completion of initial operational tests at more than 2 seconds. In other jurisdictions, existing rail regulations apply to PRT systems (see CVS, above); these typically calculate headways in terms of absolute stopping distances, which would restrict capacity and make PRT systems unfeasible. No regulatory agency has yet endorsed headways below one second, although proponents believe that regulators may be willing to reduce headways as operational experience increases.
Capacity
PRT is usually proposed as an alternative to rail systems, so comparisons tend to be with rail. PRT vehicles seat fewer passengers than trains and buses, and must offset this by combining higher average speeds, diverse routes, and shorter headways. Proponents assert that equivalent or higher overall capacity could be achieved by these means. Since there are no full-scale installations, capacity calculations are based on simulation and modeling.
Single line capacity
With two-second headways and four-person vehicles, a single PRT line can achieve theoretical maximum capacity of 7,200 passengers per hour. However, most estimates assume that vehicles will not generally be filled to capacity, due to the point-to-point nature of PRT. At a more typical average vehicle occupancy of 1.5 persons per vehicle, the maximum capacity is 2,700 passengers per hour. Some researchers have suggested that rush hour capacity can be improved if operating policies support ridesharing.
Capacity is inversely proportional to headway. Therefore, moving from two-second headways to one-second headways would double PRT capacity. Half-second headways would quadruple capacity. Theoretical minimum PRT headways would be based on the mechanical time to engage brakes, and these are much less than a half second. Although no regulatory agency has as yet (June 2006) approved headways shorter than two seconds, researchers suggest that
high capacity PRT (HCPRT) designs could operate safely at half-second headways.
In simulations of rush hour or high-traffic events, about one-third of vehicles on the guideway need to travel empty to resupply stations with vehicles in order to minimize response time. This is analogous to trains and buses travelling nearly empty on the return trip to pick up more rush hour passengers.
Light rail systems can move 7,500 passengers per hour on a fixed route. Heavy rail subways regularly move more than 12,000 passengers per hour. As with PRT, these estimates depend on having enough trains. Neither light nor heavy rail scales well for off-peak operation.
Networked PRT capacity
The above discussion compares line or corridor capacity and may therefore not be relevant for a networked PRT system, where several parallel lines (or parallel components of a grid) carry traffic. In addition, Muller estimated (see
Muller et al. TRB) that while PRT may need more than one guideway to match the capacity of a conventional system, the capital cost of the multiple guideways may still be less than that of the single guideway conventional system. Thus comparisons of line capacity should include a consideration of per line costs.
In addition, PRT systems would require much less horizontal space than existing metro systems, with individual cars being typically around 50% as wide for side-by-side seating configurations, and less than 33% as wide for single-file configurations. This is an important factor in densely-populated, high-traffic areas.
Travel speed
For a given peak speed, nonstop journeys are about three times as fast as those with intermediate stops. This is not just because of the time for starting and stopping. Scheduled vehicles are also slowed by boardings and exits for multiple destinations.
Therefore, a given PRT seat transports about three times as many passenger miles per day as a seat performing scheduled stops. So PRT should also reduce the number of needed seats for a given number of passenger miles.
While a few PRT designs have operating speeds of 100 km/h (60 mph), and one as high as 241 km/h (150 mph), most are in the region of 40–70 km/h (25–45 mph). Rail systems generally have higher maximum speeds, typically 90–130 km/h (55–80 mph) and sometimes well in excess of 160 km/h (100 mph), but average travel speed is reduced by scheduled stops and passenger transfers.
Ridership attraction
If PRT designs deliver the claimed benefit of being substantially faster than cars in areas with heavy traffic, simulations suggest that PRT could attract many more automobile drivers than other public transit systems. Standard mass transit simulations accurately predict that 2% of auto drivers will switch to trains. These same methods predict that 25% to 60% of auto drivers would switch to PRT.
Control algorithms
The typical control algorithm places vehicles in imaginary moving "slots" that go around the loops of track. Real vehicles are allocated a slot by track-side controllers. On-board computers maintain their position by using a negative feedback loop to stay near the center of the commanded slot. One way vehicles can measure their position is to add up the distance from
odometerAn odometer indicates distance traveled by a car or other vehicle. The device may be electronic, mechanical, or a combination of the two. The word derives from the Greek words ""hodós", meaning "path" or "way", and "métron", "measure".-Description:In the early autos a top reading of 99,999 was...
s, with periodic check points to compensate for cumulative errors.
Next-generation GPS and radio location can also be used for accurate positioning.
Another style of control assigns a path and speed to a vehicle, after verifying that the path does not violate the safety margins of other vehicles. This permits system speeds and safety margins to be adjusted to design or operating conditions, and may use slightly less energy.
The maker of the ULTra PRT system reports that testing of its control system shows lateral (side-to-side) accuracy of 1 cm, and docking accuracy better than 2 cm.
Safety
Computer control is considered more reliable than drivers, and PRT designs should, like all public transit, be much safer than private motoring. Most designs enclose the running gear in the guideway to prevent derailments. Grade-separated guideways would prevent conflict with pedestrians or manually-controlled vehicles. Other public transit
safety engineeringSafety engineering is an applied science strongly related to systems engineering and the subset System Safety Engineering. Safety engineering assures that a life-critical system behaves as needed even when pieces fail.- Overview :...
approaches, such as redundancy and self-diagnosis of critical systems, are also included in designs.
The Morgantown system, more correctly described as an
Automated Guideway TransitA people mover or automated people mover is a fully automated, grade-separated mass transit system.-Terminology:The term is generally used only to describe systems serving relatively small areas such as airports, downtown districts or theme parks, but is sometimes applied to considerably more...
system (AGT), has completed 110 million passenger-miles without serious injury. According to the U.S. Department of Transportation, AGT systems as a group have higher injury rates than any other form of rail-based transit (subway, metro, light rail, or commuter rail) though still much better than ordinary buses or automobiles. More recent research by the British PRT company ATS reported that AGT systems have a better safety than more conventional, non-automated modes.
As with many current transit systems, passenger safety concerns are likely to be addressed through CCTV monitoring, and communication with a central command center from which engineering or other assistance may be dispatched.
Energy efficiency
The energy efficiency advantages claimed by PRT proponents include two basic operational characteristics of PRT: an increased average load factor; and the elimination of intermediate starting and stopping.
Average load factor, in transit systems, is the ratio of the total number of riders to the total theoretical capacity. A transit vehicle running at full capacity has a 100% load factor, while an empty vehicle has 0% load factor. If a transit vehicle spends half the time running at 100% and half the time running at 0%, the
average load factor is 50%. Higher average load factor corresponds to lower energy consumption per passenger, so designers attempt to maximize this metric.
Scheduled mass transit (i.e. buses or trains,) trades off service frequency and load factor. Buses and trains must run on a predefined schedule, even during off-peak times when demand is low and vehicles are nearly empty. So to increase load factor, transportation planners try to predict times of low demand, and run reduced schedules or smaller vehicles at these times. This increases passengers' wait times. In many cities, trains and buses do not run at all at night or on weekends.
PRT vehicles, in contrast, would only move in response to demand, which places a theoretical lower bound on their average load factor. This allows 24-hour service without many of the costs of scheduled mass transit.
ATS Ltd. estimates its ULTra PRT will consume 839 BTU per passenger mile (0.55 MJ per passenger km).
By comparison, automobiles consume 3,496 BTU, and personal trucks consume 4,329 BTU per passenger mile.
Due to PRT's efficiency, some proponents say solar becomes a viable power source. PRT elevated structures provide a ready platform for solar collectors, therefore some proposed designs include solar power as a characteristic of their networks.
For bus and rail transit, energy usage per passenger-mile is dependent on service frequency and ridership, and can vary significantly from peak to non-peak. Therefore, aggregate statistics are used to calculate overall energy usage passenger-mile. In the US, buses consume an average of 4,318 BTU/passenger-mile, transit rail 2,750 BTU/passenger-mile, and commuter rail 2,569 BTU/passenger-mile.
Cost characteristics
The initial capital costs of PRT are large, but compare favorably with those of other transportation modes. Its system design tries to pay down those costs as quickly as possible, while maximizing the useful lifetime of the project. Proponents' cost estimates in passenger mile range from the cost of a bicycle (US $0.01–0.05/passenger-mile, Unimodal) to the cost of a small motorcycle ($0.20/passenger mile, TAXI 2000), and are strongly disputed by opponents. It's agreed that PRT systems require no individual license, parking or insurance fees, and buy energy in bulk from inexpensive providers.
Most of the initial investment is in guideways. Estimates of guideway cost range from US$0.8 million (for MicroRail) to $22 million per mile, with most estimates falling in the $10m to $15m range. These costs may not include the purchase of rights of way or system infrastructure, such as storage and maintenance yards and control centers, and reflect unidirectional travel along one guideway, the standard form of service in current PRT proposals. Bidirectional service is normally provided by moving vehicles around the block. To reach capacities of competing systems, a system requires thousands of vehicles. Some PRT proposals incorporate these costs in their per-mile estimates.
PRT designs generally assume dual-use rights of way, for example by mounting the transit system on narrow poles on an existing street. If dedicated rights of way were required for an application, costs could be considerably higher. If tunneled, small vehicle size can reduce tunnel volume compared with that required for an
automated people mover (APM)A people mover or automated people mover is a fully automated, grade-separated mass transit system.-Terminology:The term is generally used only to describe systems serving relatively small areas such as airports, downtown districts or theme parks, but is sometimes applied to considerably more...
. Dual mode systems would use existing roads, as well as special-purpose PRT guideways. In some designs the guideway is just a cable buried in the street (a technology proven in industrial automation). Similar technology could equally be applied to private automobiles.
A design with many modular components, mass production, driverless operation and redundant systems should in theory result in low operating costs and high reliability. Predictions of low operating cost generally depend on low operations and maintenance costs. Whether these assumptions are valid will not be known until full scale operations are commenced since reliability cannot be proven by prototype systems.
Transportation systems allocate the cost of their roads by measuring wear. PRT routes are disaggregated, and vehicles only move to carry passengers, so PRT measures wear and energy based on passengers or weight carried, rather than vehicle schedules. This brings large theoretical savings compared to trains, but appears more expensive than buses and streetcars, whose roads are subsidized by sunk, preallocated fuel taxes.
So, some planners dispute the cost-estimates of PRT when compared to
light railLight rail or light rail transit is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than traditional street-running tram systems...
systems, whose costs vary widely with non-grade-separated streetcars being relatively low cost and systems involving elevated track or tunnels costing up to US$200 million per mile.
Opposition and controversy
Opposition to PRT schemes has been expressed based on a number of concerns:
Technical feasibility debate
The Ohio, Kentucky, Indiana (OKI) Central Loop Report compared the Taxi 2000 PRT concept proposed by the Skyloop Committee to other transportation modes (
busA bus is a road vehicle designed to carry passengers. A bus seats a maximum of 8 to 300 passengers...
,
light railLight rail or light rail transit is a form of urban rail public transportation that generally has a lower capacity and lower speed than heavy rail and metro systems, but higher capacity and higher speed than traditional street-running tram systems...
and vintage
trolleyA tram, tramcar, trolley, trolleycar, or streetcar is a railborne vehicle, of lighter weight and construction than a conventional train, designed for the transport of passengers within, close to, or between villages, towns and/or cities, on tracks running primarily on streets...
). In the Taxi 2000 PRT system, the Loop Study Advisory Committee identified "significant environmental, technical and potential fire and life safety concerns…" and the PRT system was "…still an unproven technology with significant questions about cost and feasibility of implementation." Skyloop contested this conclusion, arguing that
Parsons BrinckerhoffParsons Brinckerhoff is a planning, engineering, program and construction management organization. The company has been involved in planning and designing some of the world's largest public works projects, such as Boston's Big Dig, Britain's rail system Network Rail, the Sabiya power plant in...
changed several aspects of the system design without consulting with Taxi 2000, then rejected this modified design. Despite the report's concerns regarding the implementation obstacles of PRT, the report did conclude that compared to the other alternatives, PRT offered the most acceptable point-to-point travel times, the most reliable service levels, the highest level of frequency of service and geography coverage, and was most able to maintain schedule. The report further concluded that, compared to the other alternatives, PRT would have over 3 times the ridership of the next closest alternative, including new transit riders over 9 times higher than the next closest alternative.
Vukan R. Vuchic, Professor of Transportation Engineering at the University of Pennsylvania and a proponent of traditional forms of transit, has stated his belief that the combination of small vehicles and expensive guideway makes it highly impractical in both cities (not enough capacity) and suburbs (guideway too expensive). According to Vuchic: "...the PRT concept combines two mutually incompatible elements of these two systems: very small vehicles with complicated guideways and stations. Thus, in central cities, where heavy travel volumes could justify investment in guideways, vehicles would be far too small to meet the demand. In suburbs, where small vehicles would be ideal, the extensive infrastructure would be economically unfeasible and environmentally unacceptable."
PRT supporters claim that Vuchic's conclusions are based on flawed assumptions. PRT proponent J.E. Anderson wrote, in a rebuttal to Vuchic:
"I have studied and debated with colleagues and antagonists every objection to PRT, including those presented in papers by Professor Vuchic, and find none of substance. Among those willing to be briefed in detail and to have all of their questions and concerns answered, I find great enthusiasm to see the system built."
The manufacturers of ULTra acknowledge that current forms of their system would provide insufficient capacity in high density areas such as central London, and that the investment costs for the tracks and stations are comparable to building new roads, making the current version of ULTra more suitable for suburbs and other moderate capacity applications, or as a supplementary system in larger cities.
Lessons from baggage handling
There is a history of PRT style systems constructed at airports for use in moving bags from check in to x-ray and loading points for various aircraft. Some of these systems failed or had problems and this has lead to conclusions that PRT systems would fail in a similar way.
More recently however there have also been some significant success stories in this area. The
"BagtraxTM system provided by Vanderlande Industries is successfully installed at 6 airports now. These include major airports such as Schiphol Airport in Amsterdam and Terminal 5 at Heathrow Airport, London. The performance of these modern systems exceed conventional conveyor systems by far.
Also the
"Telebag System" is operational in 5 airports including London's Luton Airport, which handles significant volumes of traffic.
The "Autover System" is another that is also used at a number of airports. At Dubai Airport for example, 31 vehicles carry 1200 pieces of luggage per hour (one piece of luggage per vehicle) from 6 origins to 24 destinations along 618 m of track making 9 loops with 16 junctions.
Regulatory concerns
Possible regulatory concerns include emergency safety, headways, and accessibility for the disabled.
For example, the California Public Utilities Commission states that its rail regulations apply to PRT, and these require railway-sized headways.
The degree to which CPUC would hold PRT to "light rail" and "rail fixed guideway" safety standards is not clear because it can grant particular exemptions and revise regulations.
If safety or access considerations require the addition of walkways, ladders, platforms or other emergency/disabled access to or egress from PRT guideways, the size of the guideway may be increased. This may impact the feasibility of a PRT system, though the degree of impact would be highly dependent on both the particular design and the municipality involved.
Concerns about PRT research
Wayne D. Cottrell of the University of Utah conducted a critical review of PRT academic literature since the 1960s. He concluded that there are several issues that would benefit from more research, including: urban integration, risks of PRT investment, bad publicity, technical problems, and competing interests from other transport modes. He suggests that these issues,
"while not unsolvable, are formidable," and that the literature might be improved by better introspection and criticism of PRT. He also suggests that more government funding is essential for such research to proceed, especially in the US.
New urbanist opinion
Several proponents of
new urbanismNew Urbanism is an urban design movement, which promotes walkable neighborhoods that contain a range of housing and job types. It arose in the United States in the early 1980s and continues to reform many aspects of real estate development and urban planning....
, an urban design movement that advocates for walkable cities, have expressed opinions on PRT.
Peter CalthorpePeter Calthorpe is an architect and urban planner, and a founding member of the Congress for New Urbanism, a Chicago-based advocacy group formed in 1992 that promotes sustainable building practices.-Biography:...
and
Sir Peter HallSir Peter Geoffrey Hall, FBA is an English town planner, urbanist and geographer. He is the Bartlett Professor of Planning and Regeneration at The Bartlett, University College London and President of both the Town and Country Planning Association and the Regional Studies Association..He is an...
have supported the concept, but
James Howard KunstlerJames Howard Kunstler is an American author, social critic, public speaker, and blogger. He is best known for his books The Geography of Nowhere , a history of American suburbia and urban development, and the more recent The Long Emergency , where he argues that declining oil production is likely...
disagrees:
"If we're going to replace the car why do it with something that's not only like the car, but not really as good as the car? It just seems crazy." He also referred to PRT proponents as
"a particular kind of crank".
Other concerns
Concerns have been expressed about the visual impact of elevated guideways and stations. The 2001 OKI Report stated that Skyloop's elevated guideways would create visual barriers, loss of privacy, and be inconsistent with the character of historic neighborhoods. Some in the business community in Cincinnati who were opposed believed elevated guideways would remove potential customers from the street level where their shops are advertised.
As with other modes of public transit, there are also concerns about policing against terrorism and vandalism. Such concerns are however of greater weight because a vandal would have the entire duration of an unaccompanied journey to inflict damage on a vehicle.
Group rapid transit
Group rapid transit (GRT) is similar to personal rapid transit but with higher-occupancy vehicles and grouping of passengers with potentially different origin-destination pairs. In this respect GRT can be seen as a sort of horizontal elevator. Such systems may have fewer direct-to-destination trips than single-destination PRT but still have fewer average stops than conventional transit, acting more as an automated
share taxiA share taxi is a mode of transport that falls between private transport and conventional bus transport, often with a fixed or semi-fixed route, but with the added convenience of stopping anywhere to pick up or drop off passengers and not having fixed time schedules...
system than a private cab system. Such a system may have advantages over low-capacity PRT in some applications, such as where higher passenger density is required or advantageous. It is also conceivable for a GRT system to have a range of vehicle sizes to accommodate different passenger load requirements, for example at different times of day or on routes with less or more average traffic. Such a system may constitute an "optimal" surface transportation routing solution in terms of balancing trip time and convenience with resource efficiency.
GRT has principally been proposed as a corridor service, where it can potentially provide a travel time improvement over conventional rail or bus and can also interface with PRT systems. However, GRT's necessary grouping of passengers makes it much less attractive in applications with lower passenger density or where few origin-destination pairs are shared among passengers.
The same passenger grouping and destination scheduling approach is used in some advanced elevators, in the form of a destination control system.
External links
Pilots and prototypes
- Austrans, Australia (9 seats per vehicle)
- Cabintaxi PRT System Hagen, Germany (see also Cabinentaxi
Cabinentaxi was a German urban transit development project, undertaken by the joint venture of Mannesmann Demag and Messerschmitt-Bölkow-Blohm under a program of the German Bundesministerium für Bildung und Forschung...
) (3 or 12 seats per vehicle)
- CyberCab PRT, Floriade 2002 Exhibition, Netherlands (5 standing)
- JPods, San Jose, CA—portable, operational rail, vehicle and software. (2 bench seats per vehicle)
- MicroRail, from MegaRail Transportation, Fort Worth, Texas (4 seats per vehicle)
- ParkShuttle GRT, Capelle aan den IJssel, Netherlands (12 seats per vehicle)
- RailCab, Paderborn, Germany—operational test track and prototypes (10 seats per vehicle)
- SkyWebExpress, Minneapolis, Minnesota, U.S.—18 metre sample guideway (3 seats across per vehicle)
- ULTra (Urban Light Transport), Cardiff Wales & Heathrow Airport, UK (4 seats per vehicle)
- Vectus Ltd., A 385 metre test track in Uppsala, Sweden (4 seats per vehicle)
- MISTER In Sept2007, Opole city main square became the show stage for MISTER prototype. MISTER news
Proposals
- Autoway—For passengers and light freights. Virginia, USA (1 adult + 1 child)
- Beamways—Suspended, dual-direction system. Sweden.
- EcoTaxi—Finnish version of PRT, termed "Automated People and Goods Movers" (APGM)
- et3 Evacuated Tube Transport "Space Travel on Earth" (tm)—automated maglev of people & cargo. Florida, USA
- SwedeTrack's Flyway- Flexible suspended PRT / GRT system from Sweden
- MagTube—a dual freight and passenger system based on maglev technology. California, USA
- RUF, Dual-mode
A dual-mode vehicle is a vehicle that can run on either a track or roadways. These include both small individual vehicles as well as larger trollies. The benefits of the tracks are: recharge batteries ; guidance; and the ability to run groups of vehicles in tight formation, which greatly increases...
—Denmark
- Skycab—A Swedish concept
- SkyTaxi— PRT+dual mode, cheap, high speed and traffic capacity, noiseless, all-weather. Moscow, Russia.
- SkyTran—a maglev system project using Inductrack
Inductrack is a completely passive, fail-safe magnetic levitation system, using only unpowered loops of wire in the track and permanent magnets on the vehicle to achieve magnetic levitation. The track can be in one of two configurations, a "ladder track" and a "laminated track"...
. Unimodal, Inc.
- Thuma—A system for varying sizes of containers
- Tritrack—Dual-mode system, but its PRT part is necessary for viability
- Proposal for Individual Sustainable Moblity (PRISM) Craig Stephan, John Miller, Jorge Pacheco, L. Craig Davis, Ford Research and Advanced Engineering; Presented at the 2003 Global Powertrain Conference
Advocacy
PRT skepticism and criticism