The Historical Emergence and
State-of-the-Art of PRT Systems

J. Edward Anderson
President, Taxi 2000 Corporation


The comfort, convenience, and privacy of the automobile has made it the preferred mode of travel in and around cities notwithstanding the extensive congestion and air pollution large numbers of automobiles produce and our increasing dependence on an uncertain supply of foreign oil1. If the situation were to remain stable, it would be bad enough, but as population increases, it will become much worse and in the long term is unsustainable. We know that the automobile must be complemented by public transit modes, but a quarter century of experience in trying to do so by reviving old modes of public transit has shown that even with enormous federal expenditures, transit use still declines2. There is and has been need for innovation. Extensive efforts are underway to innovate through intelligent transportation system (ITS) programs sponsored by the Federal Highway Administration3; but, notwithstanding mention of public transit systems in this context, there is currently no visible federally sponsored work underway on innovative public transit systems. Automated highways promise increases in flow but that must imply a greater flow into the center city and therefore greater congestion on the city streets where improved traffic signaling and one-way streets provide some relief but, with increasing numbers of automobiles, not enough to increase the average speed of traffic.

The only way to reduce congestion in the inner city is to reduce the number of automobiles, which can with today's technology be done through congestion pricing or extremely high parking charges but at the expense of downtown viability. As mentioned, attempts have been made to reduce congestion by introducing conventional rail systems, but that has not worked.

Notwithstanding long delays due to congestion, great numbers of people still prefer to drive cars while city officials are being told again and again not to look at unproven transit systems, which prevents a market for such systems from even eventually developing. To whose benefit is this?

What is needed to complement intellegent highway systems is an affordable, land-efficient transit system that reduces travel time. That system is personal rapid transit (PRT). In this paper I trace some key aspects of the history of PRT, thereby describing what it is, why it needs to be on the agenda of city planners, and why PRT is one of the keys to bringing infrastructure costs for urban transportation into the range of fiscal practicality. I discuss key elements of the history up to the present time and briefly describe the current state of the art. I then advance the view that current work on instrumented vehicle highway systems will increase in value by being complemented by PRT networks in the central city where there is very little that IVHS can by itself do to relieve congestion.

Early Government Involvement in PRT

The problem of congestion was recognized in the 1960's when Congress established the Urban Mass Transportation Administration (UMTA) and directed it to "prepare a program of research, development, and demonstration of new systems of urban transportation that will carry people and goods within metropolitan areas speedily, safely, without polluting the air, and in a manner that will contribute to sound city planning."

This directive was added to the UMTA Act with the knowledge of several new systems under development with no government support. These new systems departed from conventional exclusive-guideway transit in that they apply the key advantage of the interstate expressway to transit, i.e., while they still had stations, the stations would be placed on bypass guideways so that each trip could be taken with no intermediate stops, thus more than doubling the average speed of travel without increasing the maximum speed. It became clear that infrastructure cost could be minimized by using very small vehicles, which would have to be automatically controlled, and it was realized that the small vehicles could be used by people traveling together by choice and on-demand, i.e., with the new configuration vehicles would wait at their "off-line" stations for people rather than people for vehicles and the people could travel either alone or with one or two traveling companions, not with strangers.

The Congressional directive in the UMTA Act resulted in the award of 17 studies at $500,000 each to investigate the new systems. An optimistic report of the findings was released in 1968 in a UMTA report entitled Tomorrow's Transportation. One of these studies, performed by General Research Corporation of Santa Barbara, became widely known because it was published in Scientific American4. GRC compared the future of four U. S. cities (Boston, Hartford, Houston, and Tucson) if only conventional transit systems would be expanded with the future if the new systems, then called personal transit and later called personal rapid transit, would be installed. The conclusion was decidedly positive: Congestion would continue to worsen if only conventional systems were used, but could be reduced if the new PRT systems would be installed. Now, 28 years later, congestion has worsened substantially, but serious attempts to introduce PRT systems have stalled, not for technical reasons and not because these system would have adverse affects on communities. Indeed careful examination of the minimum use of land, material and energy possible with PRT systems and the high service level they afford shows that their impact on communities would be remarkably positive. They have been called an essential technology in a sustainable world.

The best of the PRT systems were so attractive that they were a serious threat to existing rail-transit interests. Several heavy rail programs were stopped because of interest in PRT and this ultimately caused the advocates of the old systems to lobby heavily to stop federal work on PRT, notwithstanding available information5 showing that conventional rail systems, the service concept of which was set in the days when competition was a horse cart on a mud road, would not produce significant improvements.

Early PRT Development Efforts

The first person to set down all of the essential features of PRT was Donn Fichter6. In 1953, as a transportation graduate student, young and uncommitted to any existing transit mode, he began thinking about the practical transit needs of cities. He appreciated that a new system would have to run on an exclusive guideway if it was to avoid street congestion and that to minimize the cost and visual impact of the guideway, the passenger load would have to be distributed along the guideway in many small vehicles rather than a few large ones. He opted for one-passenger cars. He appreciated that since cities are areas, not corridors, the new system would have to be a network$an interconnected network so that a passenger could be carried without stopping between any pair of stations within walking distance of the origin and the destination of the trip.

He understood that the cars would have to be automatically controlled and that a method of rapid switching with no moving track parts would be needed to permit the cars to switch from mainline to station bypass line and from one main line to another. While Fichter did not have the resources needed to build a hardware system, his well-reasoned ideas had a strong effect on subsequent development programs.

It has often been observed that when the time is right, a logical set of ideas presents itself independently to more than one mind. So it was with PRT. Also in 1953, Edward O. Haltom, a Dallas contractor wrestling with the cost of a conventional train monorail guideway, also saw the advantage of deploying many small cars. He thus conceived of a hanging-vehicle PRT system he called "Monocab," which gradually developed to the point of a full-scale test track in 1969. It was selected for deployment in Las Vegas in 1974 where a study by Peat Marwick showed that for a dollar fare it would make money.

Unfortunately foibles in human behavior combined to stop the project.

A group at General Motors in the late 1950's turned a ground-effects machine designed for the Army into an air-suspended, linear-induction-motor propelled PRT vehicle. By 1969 a spin-off company, Transportation Technology, Inc., had built a test track in Detroit. One of their systems is still in operation at Duke University Medical Center. In 1960, completely independently, William Alden conceived of a fleet of automatically controlled vehicles that could travel both on the streets and on guideways. He also found resources to build a test track and operated a vehicle on it by 1969. His system formed the basis for a government-sponsored PRT program at Morgantown, West Virginia, where due to lack of understanding of the economics of PRT the vehicle size was increased to 20 passengers, which resulted in a much larger guideway, which cost so much that no similar systems were built. Also, the vehicles were propelled and braked through wheels running on a trough guideway, which required guideway heating in the winters of Morgantown, and that markedly increased the operating cost. In 1962, also completely independently, Lloyd Berggren invented an air-suspended, air-propelled version of PRT and built a full-scale test system that operated in 1971 near Minneapolis.

Unfortunately, he found it necessary to enclose his vehicles in a tube, which after making all of the necessary engineering calculations was 7 feet wide by 14 feet high, presenting an unacceptable visual impact.

Work on PRT also began during the late 1960's in England with Cabtrack, in Japan with CVS (Computerized Vehicle System), in France with Aramis, in Germany with Cabinentaxi, and in Switzerland with ELAN. Cabtrack was tested at one-fifth scale; CVS, Aramis, and Cabinentaxi were tested full scale, and ELAN was presented in concept only. From my observations, Cabinentaxi was the most promising but it fell to the ax of a drastic budget cut in 1980.

The Aerospace Corporation PRT System

The most promising and hence from hindsight the most threatening PRT program was initiated by The Aerospace Corporation in the Los Angeles Area in 1968. Aerospace had perhaps the finest collection of scientific and engineering talent in the United States. They thoroughly absorbed the UMTA studies mentioned above, then embarked on their own comprehensive systems analysis of the needs, requirements, and technological possibilities. Like Fichter, they appreciated the need for a minimum-size guideway and for switching with no moving track parts. These needs resulted in a U-shaped guideway a bit less than one meter by one meter with vehicles riding above, and by 1970 they had built a one-tenth scale proof-of-principle system and had performed extensive analysis of the technology, planning and economics of their system. They simulated a PRT system for Los Angeles with 60,000 vehicles and 1000 stations and compared it directly with a rapid-rail plan for the same area, showing a remarkable improvement in cost-effectiveness and the feasibility of large PRT networks in handling a significant portion of the traffic in a large city.

At the University of Minnesota I was then coordinator of a Task Force on New Concepts in Urban Transportation working under a grant from the Minnesota State Legislature to develop a proposal to demonstrate an advanced form of public transportation in Minnesota. After several years of study and examination of all of the visible PRT programs around the world, in late 1973 we proposed to demonstrate the Aerospace PRT system at the Minnesota State Fair Grounds in St. Paul. In 1974, the Minnesota Legislature past an act S.F.No. 2703 that directed the development of a plan for an automated small-vehicle fixed-guideway system that would provide demand-activated origin-to-destination service. Aerospace was one of the bidders.

Instead of causing the companies who had been planning the Los Angeles rapid rail system to see the advantage of working with The Aerospace Corporation, those companies attempted to kill the PRT idea. The process was investigated and analyzed in great detail by Burke7. The problem was that the rapid-rail planning companies, who looked forward to much larger construction-engineering contracts, were expert at rapid rail and knew nothing about PRT. Moreover, they had reasonable assurance that, in those Great Society days, the UMTA Capital Grant Program would yield the funds needed to build rapid-rail systems in all major cities in the U. S., whereas PRT would at best require a development program of perhaps seven years, during which time they would be able to realize far less income. The prospect of much greater income years down the road could not compensate for expected early profits. Moreover, in vigorously resisting encroachment on their turf, a climate was created in which it was dangerous to one's career to speak positively of PRT. Since these were the established transit experts, their voices were influential in stalling consideration of PRT. One must wonder what would have happened if, in the 1890's, there had been a federal capital grant program to fund the horse and buggy.

Government Support of High Capacity PRT

Not to be deterred, The Aerospace Corporation presented their ideas to the U. S. DOT and to the White House Office of Science and Technology, busy in 1970 developing a "New Technologies Initiatives Program." As the OST leadership and consultants had not been immersed in the conventional transit industry and their detailed questions of the Aerospace team were satisfactorily answered, they recommended and President Nixon announced in his Budget Message to Congress in January 1971 a program to develop a system along the lines that Aerospace had developed8. The White House then directed UMTA to divert $20,000,000 into a High-Capacity PRT program, but UMTA leadership for their own reasons ignored the request; so OST interested NASA in PRT development. Consequently, a plan for a NASA Advanced Personal Rapid Transit Development Program was born. By Fall 1972, OST had convinced DOT to cooperate with the NASA program; however, after the November 1972 election President Nixon replaced all of his appointees with new people, who had no commitment to the budding PRT program.

Notwithstanding a "Memorandum-of-Understanding" party at NASA in December 1972, within UMTA, the NASA PRT program stalled; however, on March 27, 1973 the new UMTA administrator Frank Herringer, in testimony to Congress, made the statement: "A DOT program leading to the development of a short, one-half to one-second headway, high-capacity PRT system will be initiated in fiscal year 1974"9. PRT development was within the charter of UMTA and they were not going to let another agency take the lead. In an unexpected way the objective of OST seemed to have been realized. The program was along the lines of The Aerospace Corporation plans. The request for proposals was ready to be released in August 1974, but, because of heavy lobbying from interests fearful of becoming irrelevant if a genuine PRT program became visible, the HCPRT program was diverted into a modest technology development program. From that time forward people interested in HCPRT were unable to obtain UMTA research funding. The door was closed, not for technical reasons, but for turf protection. While extremely disappointed, The Aerospace Corporation did a great service by publishing a book10 on their work, which provides an excellent foundation for future PRT development programs.

Continued Efforts

The idea of PRT would not die; it made too much sense.

DEMAG+MBB, the developers of the German Cabinentaxi PRT system, continued to market their systems. Because they were still active and had been testing full scale since 1973, Cabinentaxi was included in 1979 in a study of automated guideway transit systems for Downtown Indianapolis, funded by the Indiana State Assembly. The 3-passenger Cabinentaxi system was found to be the most cost-effective of systems having vehicle capacities of 100, 60, 40, 20, 12 and 3 persons. The study verified the result that the total cost per passenger-mile decreased as vehicle capacity decreased. There are many reasons for this conclusion, which became apparent from a comprehensive study of the cost per passenger-mile of all transit systems11. Unfortunately, a severe economic crisis in 1980 caused the Federal Republic of Germany to cancel support of the Cabinentaxi program; however, it is still being marketed in the United States, and I wish them success. The Cabinentaxi people did a great deal of useful work that is of considerable value to that or any future PRT development program12. This is true also of many other PRT programs, most of which are reported in the proceedings of the International Conferences on PRT13.

After the Cabinentaxi program was canceled, my colleague transportation engineer, Raymond MacDonald, and I saw an opportunity to combine in a new PRT design what we had learned over the past dozen years about PRT related to required performance, design criteria, and technological advances and limitations. Beginning with the Fall Quarter of 1981, I was able to start such a design as a project in the senior mechanical engineering design program at the University of Minnesota. By Winter 1982 basic ideas I thought may be patentable had clarified and we began the patent disclosure process. By June 1982, the University of Minnesota Patent Office was sufficiently impressed that they gave me a $100,000 patent development grant, which enabled two of my best graduate students and me to spend full time for a year developing and costing the design. In June 1983, with the help of University administrators, a company was formed, which was later called Taxi 2000 Corporation. This action provided funds to enable us to continue to work full time on the project. In the Winter of 1984 the Davy McKee Corporation Chicago office became sufficiently interested to fund a larger engineering effort, which significantly advanced the details and credibility of the design. But it turned out to be difficult to raise the kind of funds needed to design and build a test system.

During the Summer of 1986, I was attracted to Boston University with the prospect of finding the necessary backing. There I had time to further the design, teach courses that attracted able students to PRT, and to make contacts with engineers in the Boston Area. From Raytheon Company, the Transportation Systems Center of the U.S. DOT, Arthur D. Little, and other organizations I found it possible to attract an excellent team of engineers and planners to further advance the design in our own free time, excited to be contributing to something really worthwhile. Within a year, because of the interest of Professor Charles Harris, we were also working with a Land Development Studio at Harvard University, which added greatly to our credibility mainly by sparking the interest of a Dutch development group. The single key factor that made progress possible in the 1980's without financial support was the ability of each of us to own a personal computer essential for the many calculations needed to round out the design. We were soon working with Raytheon executives who provided additional credibility and modest but essential resources.

As a result of contacts made in Chicago while working at Davy McKee, in May 1989 we were able to meet Gayle Franzen, recently appointed Chairman of the Northern Illinois Regional Transportation Authority. He and his predecessor Sam Skinner had been saying that they knew they could not solve the problems of transportation in the Chicago Area with only more roads and conventional rail systems and that there must be a new idea that could help. A year before, the Advanced Transit Association had completed a comprehensive study of PRT14 and had concluded that they should urge that a PRT system be demonstrated. With the essential aid of Tom Floyd15, then Chairman of ATRA, Franzen did his own investigation and became sufficiently impressed that he started a process that led in April 1990 to a request for proposals for two parallel PRT system designs.

Twelve companies submitted proposals. In cooperation with Taxi 2000 Corporation, Stone & Webster won one of the contracts, the other going to the Swiss firm Intamin A.G. The system design phase was started in March 1991 and the results were completed in Summer 1992. Unfortunately S&W could not provide matching funds for the next phase, so, in October 1992 Raytheon Company, cooperating with Taxi 2000 Corporation, was able to reenter the picture. In January 1993 Raytheon agreed to propose to be prime contractor for the second phase, which was to build a test facility and to test a PRT system based on the results of the design phase. In June 1993, the RTA awarded the test phase to Raytheon, which was underway on October 1, 1993. Raytheon redesigned the system and expects to be ready in Fall 1996 to test a system with three vehicles and one off-line station on a half-mile oval guideway at their facility in Marlborough, Massachusetts.

Largely as a result of the Chicago initiative, interest in PRT is expanding rapidly to the point that a conference will be held in Minneapolis on November 18-21 called the International Conference on PRT and Other Emerging Transportation Systems.

Work on PRT or Dual Mode systems is now underway in Sweden, England, Denmark, Finland, France, Korea, Australia, Canada and in several locations in the United States. There is now a substantial body of literature on PRT and related systems and a wide variety of implementations are being considered, some of which seem to me to have a bright future, others of which don't. The feasibility of PRT, with the right set of features, has long been shown, but there is too little agreement on the features needed to minimize costs while maintaining adequate performance.

Advice for Future PRT Developers

PRT development involves the integrated design of control systems, vehicles, guideways, stations, and maintenance facilities. Today the state of the art in microprocessors, variable-frequency drives, composites, computerized design tools, and fault-tolerant software make the development of PRT much easier than it was in 1973. From my experience, the most commonly misunderstood factor is that the design of a PRT guideway is not routine. Its cost must be minimized while meeting a complex range of criteria (I accumulated about 25 such criteria). PRT guideway design is a highly challenging task requiring the best structural engineers that can be found willing to become informed of all factors that affect the acceptability and cost-effectiveness of a design. Making use of all of the prior sources I could find, I attempted in the mid 1970's to assemble the required knowledge in a textbook16, which, as a result of further research and teaching in the area of transit systems analysis and design, I have frequently updated. Such knowledge needs to be expanded through government-sponsored research, which is now happening at least in Sweden and England.

The design and test of an economically viable PRT system that can meet all of the requirements of capacity, safety, reliability, personal security, comfort, and visual impact is a challenging task that is yet to be completed successfully. That such a design is practical I have no doubt. The problem is highly interdisciplinary and requires that the engineering team be experienced in planning PRT systems in many specific settings, working thereby with planners, developers and interested citizens so that the criteria for a successful design can be thoroughly understood.

PRT and Intelligent Vehicle Highway Systems

At the beginning of this paper, I mentioned the extensive work currently being done on intelligent vehicle highway systems.

While descriptions of that work mentions public transit systems, the only existing government support today is for planning and construction of existing transit systems notwithstanding their proven incapability of solving key problems of congestion and air pollution17. In the early 1970's the U.S. Federal Government and the Minnesota State Legislature understood the advantages of PRT systems and attempted to develop them, but at a time when there was not enough hard evidence of the inadequacy of conventional transit systems and when it was believed that money was available to deploy such systems. Today, budget balancing is the order of the day and much evidence is available of the ineffectiveness of rail systems in all but the densest cities. It needs to be recognized that a combination of IVHS, buses and PRT is the most promising means available for the solution of urban transportation problems.

In the lower-density portions of a city, automobiles and buses are essential. The problem comes in reducing congestion and air pollution in the central city. Surface-level streetcars take too much space, cause too many accidents18, are too slow, and are too expensive for the ridership they generate, and subways are prohibitively expensive. A PRT system connected with parking structures on low-cost land on the periphery of the central city can act as an efficient circulator within the central city, thus creating a remarkably improved inner-city environment. A number of studies of such systems have been made and need to be correlated with the extensive research underway on IVHS. Only in this way, I believe, can many of the problems of the inner city, which are usually transportation-related, be solved.

Based on past experience, it is essential that any government program involving PRT be managed out of an organization devoted only to R&D, not to providing capital grants for existing systems. Political deadlines must be avoided. In a manner similar to the old National Advisory Committee for Aeronautics, the predecessor of NASA, such an organization should do the analysis and testing needed to optimize PRT systems but should leave the demonstration of such systems to private industry.

PRT and IVHS people can and need to work together for the benefit of cities everywhere. To adapt an old phrase: "United we can succeed, divided we will fail."