This is a Panel Report from a study entitled Automated Guideway Transit: An Assessment of PRT and Other New Systems, United States Congress, Office of Technology Assessment, June 1975, pp 12-16, U.S. Government Printing Office, Washington, D.C.


Since the term "Personal Rapid Transit" first entered the transit vocabulary in 1968, this highly innovative concept has fascinated many transportation planners. PRT offers personalized service with small vehicles which provide non-stop transportation from origin to destination at short headways. To date, no systems which can be classified as PRT are in revenue service or under construction in the United States, but several test track installations have been built in Europe and in Japan.

Proponents of PRT view this concept as a reasonable supplement to the private automobile in high density urban areas (i.e. greater than 3,000 persons per square mile) and claim that PRT can provide a very much higher level of service than other modes of public transportation. Thus, it is argued that PRT systems would attract a significant percentage of the rides now being made in private automobiles and offer obvious benefits:

It is also contended that PRT would provide greater mobility for the transportation disadvantaged, i.e., the young, the elderly, the poor, and the handicapped.

Proponents admit that the area-wide networks with closely spaced stations and large numbers of vehicles would be expensive to build and, perhaps, to operate. The initial capital cost might equal that of rail rapid transit systems, but levels of service are envisaged to be much higher than with conventional modes, except perhaps taxicabs. Proponents claim the higher service levels will attract significantly greater patronage than conventional transit. Automation is expected to allow the high service level to be delivered at a cost the public is willing to pay.

PRT capacity depends upon short headways: Except in downtown areas, headways need not be closer than those of GRT systems (i.e., three seconds). In downtown areas, headways on the order of 1/2 second would be needed to move 10,000 people per hour over a single PRT guideway at an average occupancy of 1.4 people per vehicle. This is roughly equivalent to the number of people moved on four freeway lanes.

Advocates of PRT have estimated that there are 10,000 square miles of urban areas in the United States where PRT service might be appropriate. This would require about 20,000 miles of one-way guideways and about three million PRT vehicles.


Because there are no operating systems, there is no empirical evidence on PRT. Many of the studies reviewed were motivated by attempts to sell or reject the concept and were based upon largely arbitrary assumptions. Therefore, there are many detailed issues for which objective data are needed.

Technical -- With few exceptions, the engineers and manufacturers who have made serious studies of the PRT concept find that there are numerous technical problems that must be solved before PRT systems can be deployed. Technical solutions have been proposed but not validated, and a large program of development testing and demonstration would be needed to implement a PRT system. Estimates of time and money required to achieve market-ready systems vary widely. However, there appears to be general agreement that at least 10 years would be required depending upon the level of funding provided.

The following technical problems need to be solved:

Economic -- The economic characteristics of PRT are so unclear that meaningful analysis is difficult. Several analyses have been attempted, including one by the Aerospace Corporation for the Los Angeles area, a general study by the DOT Transportation Systems Center (TSC), and one of the Twin Cities area by De Leuw Cather. Cost assumptions vary greatly. Proponents' estimates for PRT vehicles, for example, are based upon large production runs, and the estimated cost per unit presumably goes down with increased production. As another example, costs are related to solutions to potential social problems. If passenger security considerations require the installation of closed circuit T.V. throughout the system, including vehicles, then the costs would rise appreciably. Costs for operation and maintenance also vary. Proponents' estimates assume maintenance levels that are unrealistically low for transit.

The major economic issue is whether research. without hardware development and urban demonstration, can answer the economic questions, or whether hardware development is necessary to assess the economic characteristics of PRT systems.

Social -- Public acceptance of PRT is open to question. Despite the many potential advantages of PRT in comparison to other transit modes, there is a serious question that the associated proliferation of elevated guideways and stations would be acceptable to the public, particularly in residential neighborhoods. Also, the safety and security aspects of unattended small vehicles require careful evaluation.

Advocates contend that PRT should duplicate as closely as possible the service characteristics of the private automobile. The wisdom of attempting to provide such a high level of service at public expense is open to question. Whether the benefits of such a system would only accrue to the well-to-do or whether they would also provide for the needs of the transit disadvantaged is worthy of exploration. An annual expenditure equal to the debt service on the capital cost of such a high technology system, when combined with traffic management systems designed to enhance conventional transit, might provide better service at lower cost over a larger service area, than PRT. These observations may be equally true for other capital intensive systems. Such tradeoff studies should be undertaken and clear urban transit goals articulated by UMTA before the agency embarks on new systems for their own sake.

The major social issues of PRT are summarized as follows:

Institutional -- Groups in Germany, Japan and France are actively engaged in PRT research and development. The possibility of cooperative arrangements between United States firms or the United States Government and their overseas counterparts thus exists. Such efforts, building upon United States experience and accomplishments in SLT and GRT and overseas research in PRT, could lead to stronger and more cost-effective development programs. On the other hand, the United States has pioneered much of the work in new transportation systems and could develop the technology if a need exists for PRT.

The effect on U.S. balance of payments must be considered if equipment licenses or royalty payments for the use of foreign patents are required. Such payments, however, will be only a small part of the costs for building a system because most transit system costs are for construction. Thus, potential foreign exchange savings are too small to justify a large investment in domestic R & D. PRT poses major institutional issues as follows:


Before major commitments of funds are made for detailed simulations or hardware developments, research is required to resolve the many uncertainties concerning the proper role of PRT systems, their social acceptability and their economic feasibility. These preliminary studies may involve expenditures of $4 to $6 million.

There are possibilities for cooperation with foreign governments or overseas suppliers in research and development of PRT. UMTA has recognized these possibilities in starting negotiations with the West German Government.


Last modified: September 19, 1998