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Personal rapid transit (PRT) is a category of proposed public transport modes designed to offer automated, on-demand, and non-stop transportation on a network of specially built guideways. The concept dates back to the mid 1960s, and has been independently reinvented many times since then. Although elements of PRT design have influenced the design of some existing people mover systems, and several fully automated mass transit systems exist, as of 2006 no PRT project has progressed beyond the prototype stage.

The design concepts and engineering challenges of PRT are well understood, but questions remain concerning actual production and operational costs, safety, aesthetics, and public acceptance. The concept is considered controversial partly because there has never been a real-world installation to confirm of cost and ridership predictions. Past projects have failed due to: lack of financing, cost overruns, regulatory conflicts, political interference in the design requirements, and flaws in engineering or design. There is also opposition from advocates of other transport modes.

Two projects are currently under development: one at Heathrow Airport in London , scheduled to come into operation in 2007; and another at Dubai International Financial Center in Dubai scheduled to come into operation in 2008.

Overview

The PRT concept is designed to satisfy the divergent geographic and chronologic requirements of users by incorporating off-grade guideways, off-line access points, and small, fully-automated vehicles whose size would discourage unrelated riders in the same vehicle. By doing so, PRT vehicles on main guideways would not be free of both non-PRT traffic and other PRT vehicles entering or exiting the main guideway. Small vehicles would ensure few passengers per vehicle, encouraging single destination trips, i.e where all the passengers in the vehicle are going to the same place. These features are intended to keep the average end-to-end speed high and relatively uniform from day to day.

The diagram (right) shows a highly simplified PRT system serving a small urban community. The depiction shows two interconnected loops. This is highly simplified to help visualize the concept and a real-world installations would be vastly more complex in every respect.

Assuming all modes of tranportation serve the same area surrounding each access point, a private automobile, presumably, offers the highest level of time independence and possible points of origination and destination. On the other hand, according to PRT proponents, trains and light-rail systems offer the least time independence and fewest possible points of origination and destination. Somewhere between the two, a PRT system would place small access points within a reasonable distance of a significant number of homes and businesses.

PRT has similarities to and differences from other forms of transport. To compare the proposed features:

History

The basic concept of PRT was proposed by some inventors in early 1950. Don Fichter, a city transportation planner, wrote a book entitled "Individualized Automated Transit in the City" in 1964. It is originally proposed as a public transit system for areas of medium to low population density, in a 1968 report of US Department of Housing and Urban Development, "Tomorrow's Transportation: New Systems for the Urban Future". This report was related to government funding for prototypes in US and other countries. Today, the concept of PAT (Personal Automated Transport) is often used to describe automated personal transportation systems for both passengers and freights.

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. Members of the study team published in Scientific American in 1969, the first wide-spread publication of the concept. The team subsequently published a text on PRT entitled Fundamentals of Personal Rapid Transit.

The Morgantown Personal Rapid Transit project has been in continuous operation at West Virginia University in Morgantown, West Virginia since 1975, with about 15,000 riders per day (as of 2003). The vehicles are rubber-tired and powered by electrified rails. Steam heating keeps the elevated guideway free of snow and ice. Most WVU students habitually use it. This system was not sold to other sites because the heated track has proven too expensive. The Morgantown system demonstrates automated control, but authorities no longer consider it a true PRT system. Its vehicles are too heavy and carry too many people, making it more similar to light rail schemes. Most of the time it does not operate in a point to point fashion for individuals or small groups, running instead like an automated people mover or elevator from one end of the line to the other. It therefore has reduced capacity utilization compared to true PRT. Morgantown vehicles also weigh several tons and run on the ground for the most part, with higher land costs than other systems.

The Aramis project in Paris, by aerospace giant Matra, started in 1967, spent about 500 million francs, and was cancelled 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.

A project called Computer-controlled Vehicle System (CVS) operated in Japan from 1970 to c.1978. In a full scale test facility, 84 vehicles operated at speeds up to 60 km/h on a 4.8 km guideway; 1 second headways were achieved during tests. Another version of CVS was in public operation for six months during 1975–76. This system had 12 single-mode vehicles and 4 dual-mode vehicles on a one mile track with five stations. This version had over 800,000 passengers. CVS was cancelled when Japan's Ministry of Land, Infrastructure and Transport adjudged it unsafe under existing rail safety regulations, specifically in respect of braking and headway distances.

In Germany, the Cabinentaxi project, a joint venture from Mannesmann Demag and MBB, created an extensive PRT development in the 1970-80s considered fully developed by the German Government and its safety authorities. This project was canceled when a disagreement over the site for the initial implementation coincided with non-defense budget cuts by the German government.

In the 1990s, Raytheon invested heavily in a system called PRT2000 that was based on technology developed by J.Edward Anderson at the University of Minnesota. Raytheon failed to install a contracted system in Rosemont, Illinois, near Chicago, when estimated costs escalated to $50,000,000 per mile, allegedly due to design changes that increased the weight and cost of the Raytheon system relative to Anderson's original design This system may be available for sale by York PRT. In 2000, rights to the technology reverted to the University of Minnesota, and were subsequently purchased by Taxi2000.

The UniModal (also known as SkyTran) project, originated by Douglas Malewicki, proposes using Inductrack passive magnetic levitation in vehicles with few moving parts to achieve speeds of 100 mph (161 km/h). Its assumptions of capacities are based on these speeds and on half-second headways, and includes many other hypothetical features such as speech recognition. Malewicki acknowledges that this is at present a paper concept, and no prototype yet exists.

In 2002, 2getthere, a consortium of Frog Navigation Systems and Yamaha, operated "CyberCabs" at Holland's 2002 Floriade festival. These transported passengers up to 1.2 km on Big Spotters Hill. CyberCab is like a Neighborhood Electric Vehicle, except it steers itself using magnet guidance points embedded in the lane.

In 2003, Ford Research proposed a dual-mode system called PRISM. It would use public guideways with privately-purchased but certified dual-mode vehicles. The vehicles would be less than 600 kg (1200 lb), allowing small elevated guideways which could use centralized computer controls and power.

In January 2003, a prototype ULTra ("Urban Light Transport") system from Advanced Transport Systems Ltd in Cardiff, Wales was certified to carry passengers by the UK Rail Inspectorate on a 1 km test track. It had successful passenger trials and has met all project milestones for time and cost.

ULTra was recently (October, 2005) selected] by BAA plc for London's Heathrow Airport. This system is planned to transport 11,000 passengers per day from remote parking lots to the central terminal area. PRT is favored because of zero on-site emissions from the electrically powered vehicles. PRT will also increase the capacity of existing tunnels without enlargement. BAA plans begin operation by the end of 2007 and to expand the system in 2009.

Vectus Ltd., a Korean/Swedish consortium, is constructing (2006) a test track in Sweden.

PRT System Design

There are currently no agreed-upon standards in 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 contentious.

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 economical (for example, when the system at West Virginia University moved from 6-passenger to 20-passenger vehicles, point-to-point operations were largely abandoned). Against this, smaller vehicles are more affected by air resistance, which dominates the energy cost of keeping vehicles moving at speed. Larger motors are also generally more efficient than smaller ones.

The number of riders who will share a vehicle is thus a key unknown variable. Until a public system is operating, this can only be estimated because ridership cannot be directly extrapolated from fixed-route, Mass Transit, systems such as buses and trains or from private automobile usage. Some designers use private automobiles as an analog to estimate potential PRT ridership. For example, in the U.S., the average private automobile carries 1.16 persons, and most industrialized countries commonly average below 2 people. Thus, some PRT designers choose an optimum vehicle capacity of 2 passengers or even a single passenger, notably designs by UniModal / SkyTran. Other designs choose larger vehicles, making it possible to accommodate families, riders with bicycles, and disabled passengers with wheelchairs. As of 2006 all systems known to be under active development use 4-passenger vehicles.

Propulsion

All current designs are powered by electricity, generally transmitted via lineside conductors rather than using on-board batteries, to reduce vehicle weight. According to designer of Skyweb/Taxi2000, J.E. Anderson, the lightest-weight 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 PRT designs use rotary motors.

Switching

Most PRT designers avoid track switching, preferring vehicle-mounted switches or conventional steering. The reasons are multiple. PRT designers say that track switching complicates the guideway, making junctions more visually obtrusive and malfunctions impact all vehicles approaching the failed junction. Track switching requires more complex failure detection and adequate warning time to allow approaching vehicles to stop before reaching the failed junction. By using vehicle-mounted switching, guideway design is simplified and switch position detection is faster thus allowing closer spacing of vehicles. Switch failures are also limited only a single vehicle and don't interfere with other vehicles.

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. Overhead suspended vehicles are said to unload the skins of the vehicle, which can therefore be lighter since many materials are stronger in tension than they are in compression. 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. Following some issues with prototypes many also aim to be self clearing in bad weather.

Stations

Stations are usually proposed to be frequent, 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 1/3 of the vehicles in a system being stored at stations waiting for passengers. Embarkation stations are not envisaged to include facilities such as rest rooms. For elevated stations, an elevator may be required for accessibility.

Some designs have included substantial extra expense from the track needed to decelerate 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 footprint.

Operational Characteristics

Headway Distance

"Headway Distance" can mean "distance/time between vehicles (front to back)" or "distance/time between the fronts of vehicles (front to front)". Usually the latter is referred to when talking about capacity and vehicle frequency.

Spacing of vehicles on the guideway influences the maximum passenger capacity of a track, so designers aim to minimize the headway, the distance between the vehicles. 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. Some regulators (e.g. the British Rail inspectorate, regulating ULTra) are willing to accept two second headways. In other jurisdictions rail regulations apply to PRT systems (See CVS, above); these typically calculate headways in terms of absolute stopping distances and may make PRT systems uneconomical. No regulatory agency has yet endorsed headways as short as one second. Regulators may be willing to reduce headways with increased operational experience.

Capacity

PRT is usually proposed as an alternative to rail systems, so comparisons tend to be with rail. Since there are no full-scale installations, capacity calculations are based on simulation and modelling and are contested by skeptics. PRT vehicles seat fewer passengers than trains and buses, and must offset this by higher average speeds and shorter headways. Proponents assert that equivalent or higher overall capacity could be achieved by these means.

With two-second headways, an average of 1.5 persons per vehicle implies a maximum capacity per guideway route of 2,700 passengers per hour, dependent on having sufficient vehicles available. In simulations of rush hour or high-traffic events, about 1/3 of vehicles on the guideway need to travel empty to resupply stations with vehicles in order to minimize response time.

Light rail systems can achieve capacities over 7,500 passengers per hour under normal operations. Heavy rail subway systems regularly transport 12,000 passengers per hour or more. Neither light nor heavy rail scales well for off-peak operation.

Travel Speed

For a given peak speed, point-to-point journeys are quicker than scheduled stopping services. While a few PRT designs have operating speeds of 60 mph, most are in the region of 25-45 mph. Rail systems generally have higher maximum speeds, typically 55-80 mph and sometimes well in excess of 100 mph; but average travel speed may be reduced by the need to stop at all stations, as well as the need for passengers to transfer.

Ridership Attraction

If PRT designs ultimately deliver the claimed benefit of being substantially faster than cars in areas with heavy traffic, simulations suggest that PRT might attract significantly higher than the predicted mode switch from private motoring than is the case for other proposed public transit systems (figures between 25% and 60% have been discussed).

Against this, the relationship of delays to traffic density for road travel is observed to be non-linear and the congestion delays which give rise to the predicted attraction may be eroded. London's Congestion Charge achieved approximately 20% reduction in private motor traffic, with an immediate and measurable improvement in journey times for all road transport in the City. This was achieved without substantial up-front investment, although revenue raised has been re-invested in additional public transport capacity.

Control Algorithms

One possible 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 keep track of their position is by integrating the input from speedometers, using periodic check points to compensate for cumulative errors.

Another style of algorithm assigns a trajectory to a vehicle, after verifying that the trajectory does not violate the safety margins of other vehicles. This system permits system parameters 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 engineering approaches, such as redundancy and self-disagnosis of critical systems, are also included in designs.

The Morgantown system, more correctly described as an Automated Guideway Transit 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.

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.

Cost Characteristics

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. In high-traffic single-point destinations, such as stadiums, multiple larger stations would be needed, and in major transport corridors or congested central business districts, additional guideways and stations would be needed, increasing the costs. These estimates do not account for cost overruns common in public projects and new technologies and are considered low by skeptics. Further, to reach capacities anywhere approaching competing systems, a system requires of the order of thousands of vehicles. Some PRT proposals may 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 tunnelled, small vehicle size can reduce tunnel volume compared with that required for an automated people mover (APM). 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. There are already some operational driverless transit systems, mostly at airports and tourist attractions. Cost data from these small-scale systems indicates that while automation reduces labor costs by eliminating drivers, these savings are eroded by increased vehicle maintenance and system monitoring. It is not clear whether larger systems would have the same maintenance and monitoring inefficiencies.

Predictions of low operating cost generally depend on low operations and maintenance costs (O&M). Whether these assumptions are valid will not be known until full scale operations are commenced since assumptions regarding reliability cannot be proven by prototype systems; U.S. federal data shows that O&M costs are nearly constant per seat for a wide variety of systems: buses, trains, aircraft and private automobiles. Low operating cost projections also depend on relatively high capacity utilization (for a public transport system) delivered through on-demand service.

Some planners dispute the cost-estimates of PRT when compared to light rail 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. Systems such as streetcars, which run over the road network, and buses, require no further rights of way, which can represent a substantial cost saving over those requiring new, dedicated routes.

Ridership and cost

For scheduled mass transit such as buses or trains, there is a fundamental tradeoff between service and cost. This is due to the fact that buses and trains must run on a predefined schedule, even during non-peak times when demand is low and vehicles run nearly empty. For this reason, transportation planners typically control costs by attempting to predict periods of low demand, running on reduced schedules and/or with smaller vehicles at these times. This, however, increases wait times for passengers. In many cities, trains and buses do not run at all at night or on weekends, because the low demand does not justify the cost.

PRT vehicles, in contrast, would only run in response to demand, allowing 24-hour service without many of the cost implications of scheduled mass transit.

Proposals

ULTra

ULTra ("Urban Light Transport") is a system from Advanced Transport Systems Ltd in Cardiff, Wales. The ULTra system differs from many other systems in its focus on using off-the-shelf technology and rubber tires running on an open guideway. This approach has resulted in a system that is more economical than designs requiring custom technology. ULTra was recently (October, 2005) selected] by BAA plc for London's Heathrow Airport.

Cabinentaxi Main article: Cabinentaxi.

Cabinentaxi was a German urban transit development project, undertaken by the joint venture of Mannesmann Demag and MBB under a program of the German BMFT (German Ministry of Research and Development.)

UniModal / SkyTran

main page: UniModal

UniModal or SkyTran is a concept by Douglas Malewicki for a 160km/h (100mph) personal rapid transit system that would use electric linear propulsion and a form of passive magnetic levitation called Inductrack.

Opposition and controversy

Opposition has been expressed to PRT schemes and their proponents 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 (bus, light rail and vintage trolley). Consulting engineers with Parsons Brinckerhoff found the Taxi 2000 PRT system had "...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 disputed this conclusion.

Vukan R. Vuchic, Professor of Transportation Engineering at the University of Pennsylvania and a proponent of light rail, has stated that "the PRT concept is imagined to capture the advantages of personal service by private car with the high efficiency of rapid transit. Actually, 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." This has prompted a debate between Vuchic and PRT proponents

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.

Regulatory concerns

Possible regulatory concerns include emergency safety, headways, and accessability for the disabled. 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 is substantially increased. Because minimizing guideway size is important to the PRT concept and costs these concerns may be significant barriers to PRT adoption. The US and Europe both have legislation mandating disabled accessibility for public transport systems.

For example, the California Public Utilities Commission states that its "Safety Rules and Regulations Governing Light Rail Transit" (General Order 143-B) and "Rules and Regulations Governing State Safety Oversight of Rail Fixed Guideway Systems" (General Order 164-C) are applicable to PRT . Both documents are available online . The degree to which CPUC would hold PRT to "light rail" and "rail fixed guideway" safety standards as a condition for safety certification is not clear.

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 would be inconsistent with the character of historic neighborhoods. Some in the business community in Cincinnati were opposed to Skyloop's elevated guideway because it would remove potential customers from the street level.

As with other modes of public transit, there are also concerns about policing against terrorism and vandalism. Israeli proponents say that PRT may protect against terrorism by reducing the scope of vehicle that can be attacked.

Some have also objected to PRT promotion on the grounds that it is a distraction from other, more proven transit solutions. Objectors claim that advocacy for PRT has reduced support for other alternatives to private motoring, with the result that neither alternative has been implemented.

See also

• Morgantown Personal Rapid Transit, 1975-present
• Cabinentaxi - 1970s West German PRT system.
• UniModal - hypothetical implementation.
• People mover
• Light Rail

External links

Pilots and prototypes

• Austrans, Australia
• ULTra (Urban Light Transport), Cardiff Wales, UK
• ParkShuttle, Capelle aan den IJssel, Netherlands
• MicroRail, from MegaRail Transportation, Fort Worth, Texas
• Postech, Pohang University, Korea
• SkyWebExpress, Minneapolis, Minnesota, US. 18-meter sample guideway.

Proposals

• Autoway— For passengers and light freights. Virginia, USA.
• EcoTaxi — Finnish version of PRT, termed "Automated Goods & People Mover" (APGM).
• RUF, Dual-mode — Denmark.
• Intelligent Transportation - Ultra light, passenger and cargo networks
• Skycab — A Swedish concept
• Skytran
• Thuma —A system for varying sizes of containers.
• Tritrack — Dual-mode system, but its PRT part is necessary for viability.
• UniModal — California & Montana, US; New Delhi, India.
• Vectus Ltd. — Has 385 meter test track under construction in Uppsala, Sweden.

Advocacy

• ATRA, The Advanced Transit Association, a professional group.
• CPRT, Citizens for Personal Rapid Transit (US)
• Get There Fast, Seattle, WA
• Get On Board Personal Rapid Transit, Seattle, WA PRT news & analysis
• Innovative Transportation Technologies web site by Jerry Schneider.
• Open Directory: Personal Rapid Transit
• PRT Wiki
• Transportationet PRT from engineering and law point of view. Site by Oded Roth, member of Israeli Retzef team.
• Skyloop
• A Review of the State of the Art in PRT Systems, J. E. Anderson; Journal of Advanced Transit 34:1(2000)

PRT Skepticism and Criticism

• Light Rail Now "Personal Rapid Transit – Cyberspace Dream Keeps Colliding With Reality"
• Personal Rapid Transit PRT Skeptic Page
• Monorail, PRT, AGT, and "Gadget Transit" Analyses — several Light Rail Now articles skeptical of PRT
• Transit for Livable Communities resolution opposing public funding for PRT
• Planetizen Article on PRT and "Gadgetbahnen"
• Public Transit gadgetbahn articles
• The Road Less Traveled: The pros and cons of personal rapid transit." by Troy Pieper

References

1. Irving, Jack (1978). "Fundamentals of Personal Rapid Transit". D.C. Heath and Company. {{cite web}}: Unknown parameter |accessyear= ignored (|access-date= suggested) (help); Unknown parameter |coauthors= ignored (|author= suggested) (help)
2. Samuel, Peter (1996). "Status Report on Raytheon's PRT 2000 Development Project". ITS International. {{cite web}}: Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
3. Samuel, Peter (1999). "Raytheon PRT Prospects Dim but not Doomed". ITS International. {{cite web}}: Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
4. "Personal Automated Transportation: Status and Potential of Personal Rapid Transit, p.89" (PDF). Advanced Transit Association. 2003. Retrieved 25 March. {{cite web}}: Check date values in: |accessdate= and |year= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)CS1 maint: year (link)
5. "Infrastructure cost comparisons" (Microsoft Word). ATS Ltd. Retrieved 25 March. {{cite web}}: Check date values in: |accessdate= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
6. NY Times
7. newmassmedia.com
8. evworld.com
9. globalideasbank.com
10. "Ohio, Kentucky, Indiana (OKI) Central Loop Report". {{cite web}}: Unknown parameter |accessyear= ignored (|access-date= suggested) (help); Unknown parameter |yesr= ignored (help)
11. "A Rebuttal to the Central Area Loop Study Draft Final Report" (PDF). 2001. {{cite web}}: Unknown parameter |accessyear= ignored (|access-date= suggested) (help)
12. Vuchic, Vukan R (September/October, 1996). "Personal Rapid Transit: An Unrealistic System". Urban Transport International (Paris), (No. 7, September/October, 1996). {{cite web}}: Check date values in: |date= (help); Unknown parameter |accessyear= ignored (|access-date= suggested) (help)CS1 maint: date and year (link)
13. Anderson, J.E. (December 22, 1996). "Personal Rapid Transit: A Response to Professor Vukan R. Vuchic". Urban Transportation Monitor.{{cite web}}: CS1 maint: date and year (link)
14. Vuchic, Vukan R. (December 22, 1996). "Personal Rapid Transit Works in Simulation Only - An Answer to Professor J. Edward Anderson". Urban Transportation Monitor.{{cite web}}: CS1 maint: date and year (link)
15. Anderson, J.E. "A Second Response to Professor Vuchic's Comments on Personal Rapid Transit".
16. ^ Light Rail Now article containing image (above right) - a Raytheon PRT design superimposed on a real street.

Additional references

• Transit Systems Theory, J.E. Anderson, 1978
• Control of Personal Rapid Transit Systems, J.E. Anderson, 2003 (PDF)
• Systems Analysis of Urban Transportation Systems, Scientific American, 1969, 221:19-27
• Individualized Automated Transit in the City, Don Fichter, 1964

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