A PRT Deployment Strategy to Support Regional Land Use and Rail Transit Objectives


J.B. Schneider

Professor Emeritus, University of Washington, Seattle

This article was published originally in 1992 in Transportation Quarterly, 46:1, pp 135-53. Reprints are available from the Eno Transportation Foundation, Inc. (http://www.enotrans.com) Posted with permission from the Eno Transportation Foundation

After a decade or more of neglect, a resurgence of interest in Personal Rapid Transit (PRT) technologies seems to be in the air. The West Germans proved that PRT is technically feasible with their Cabintaxi technology test track and test program during the late 1970's [1]. However, public acceptance questions cannot be answered until a PRT system, designed for use by the general public, becomes operational. Currently, it appears that a major research and development program sponsored by the Regional Transportation Authority that serves the Chicago suburbs may provide some answers to both technical and public acceptance questions during the next several years.

While waiting for these results, it is important to reexamine questions regarding the appropriate role of PRT in meeting some of the mobility needs of major U.S. metropolitan areas. Until such questions are answered satisfactorily, PRT will continue to be regarded by many people as a solution in search of a problem rather than as a technology that can be an important contributor to meeting the urban mobility needs of the 1990's and assisting in creation of less auto-oriented, auto-dependent cities

In the past, advocates of PRT have argued that PRT should replace conventional rail transit as the primary transit technology of the future [2]. They have suggested that it be deployed initially in the central business district (CBD) of a metropolitan area and then be gradually expanded outward to cover the entire metropolitan area. Many of these arguments are sound and quite persuasive. And, many of them continue to be validated by the poor performance of conventional transit [3]. Since no PRT system has yet been built in the United States, it has not yet had the chance to prove its worth to those who are not yet convinced that it will perform as predicted. For this reason, PRT is not seen today as a prime contender for a major role in serving urban transit mobility needs by most citizens and public officials, both local and federal.

Clearly, supporters of conventional transit technologies are having a difficult time getting funding and building systems that perform as well as advertised. But, cities all over the country continue to clamor for funds to construct rail transit systems, mainly because the public firmly believes that rail transit is the answer to most urban congestion problems [4]. Given this often unquestioning public support, it is likely that rail systems will continue to be built, mostly in low density western U.S. cities, providing that sufficient funds can be obtained from the voters. If this is true, then the relevant question for those interested in PRT is: How can PRT be deployed to assist and enhance the performance of these new rail transit lines?

The purpose of this article is to outline a PRT deployment strategy that will allow those interested in conventional rail and PRT to join forces and work together to increase transit's share of the urban mobility market during the 1990s and beyond.


Any rational transportation development strategy should be based on a sound and widely accepted land-use strategy. The philosophy of this position is that transportation investments should be made to support the achievement of land-use objectives. Unfortunately, many metropolitan areas do not have a well-defined land-use plan in place. However, those that do have usually adopted a strategy that calls for the creation of an urban form that may be called the "polycentric city." Although this idea has appeared in many forms in the literature during the past several decades, Victor Gruen presented one of the earliest coherent rationales for this urban form concept in 1973 [5].

A more theoretical rationale, based on economic principles and central place theory, has been devised by Parr and others [6]. This strategy calls for the designation of a hierarchy of growth centers within the metropolitan region. The historic CBD of the region stands at the top of the hierarchy while more numerous regional, community and local centers constitute the lower levels of the hierarchy.

Figure 1 illustrates this concept in diagrammatic form and shows one version of how these centers could be spatially arranged to provide an efficient urban form. Clearly, there are many factors that prevent this idealized urban form from actually occurring but there is considerable evidence available that shows that modified versions of it are emerging in several U.S. metropolitan regions [7]. An example of this evidence is given in Figure 2, which shows the locations of substantial outlying "centers" in relation to the historic CBD in several U.S. cities [8]. Many authors have written about the transition of the U.S. city from an essentially monocentric to a polycentric urban form during the past two decades and it is generally predicted that the urban form of the future is going to be even more polycentric than it is at present [9].

In a few U.S. cities, regional planning agencies have formally defined and adopted a land-use plan that is designed to foster the rapid growth of those locations within the region that have been designated as centers. The main idea is to provide various incentives that will attract developers to these locations while discouraging growth in other parts of the region, particularly in outer suburban or fringe areas. This would increase the density of the designated centers (both housing and jobs), combat further urban sprawl and make it more likely that a mass transit system can be designed that will have some chance of being "successful" in that it will take many cars off the road. Figure 3 is a map that shows the locations of several centers that have been identified by the Metropolitan Council of the Twin Cities, in Minnesota. Other cities that have developed a centers land-use plan include Baltimore, Denver, Phoenix, Seattle, Toronto, Vancouver, B.C., and many others [10].

To date, the city that has taken the centers concept most seriously is Toronto. In 1978, the metropolitan government in Toronto adopted a structure plan that called for creation of two major outlying centers (North York and Scarborough) and also designated several intermediate centers [11].  The objective was to attract about 30,000 jobs to each of the two major centers and to increase their density as part of an areawide growth management strategy. Figure 4 shows the locations of these outlying centers as well as the intermediate centers that were selected for special attention. By and large, this plan has been successful in attracting growth during the past 12 years, as each of the major centers now includes about 18,000 jobs. And, the growth target for the North Yonge Centre was recently raised to 60,000 jobs.

In the United States, the centers concept continues to be quite popular but there have not been any serious attempts to implement it. This is not because the regional planning agencies do not want to implement the concept. They simply do not have the authority and resources needed to do the job. Still, the concept continues to appear in land-use plans, sometimes in map form, produced by Metropolitan Planning Organizations (MPOs). It seems to be the only urban form concept that is of particular interest to those land-use planners who work at the metropolitan scale. It is commonly employed in other countries around the world as well. For example, the centers concept is the centerpiece of the recently adopted land-use plan for Metropolitan Tokyo [12].


If done properly, the transportation component of the metropolitan plan should be designed to implement the desired metropolitan-scale land-use (urban form) objectives of the area. Today, most metropolitan areas do not have the resources needed to expand the highway system greatly. Growing public concern about suburban congestion, global warming, air quality and other auto-generated adverse impacts is also reducing the prospects for building more highways. Concurrently, there is substantial interest in many U.S. cities in building new and/or expanding existing mass transit facilities. In response to this interest, transportation planners are using a concept that calls for the construction of several mass rail transit lines that are radial to the region's CBD and that connect it with one or more of the centers designated by the land-use planners. Figure 5 is an abstract illustration of this idea. Short-hand terms for this concept are "cluster-and-connect" or "pearls-on-a-string." Figure 6 shows how this concept has been used by the Denver Regional Council of Governments in a study designed to identify one high-priority corridor for an initial rail transit investment. Several other U.S. cities are using this concept in a similar fashion.

This approach is supportive of a centers land-use policy in that many (not all) rail stations would be located in or adjacent to designated centers and would provide some additional stimulus for them to grow rapidly and become more dense. Since higher levels of density usually produce higher levels of mass transit use, these two policies are viewed as being mutually supportive. Thus, such investments in rail transit are seen by land-use planners as an important tool that can be used to assist the implementation of a centers land-use plan. Furthermore, such transit investments can be, and often are, cited as an anti-sprawl growth management tool.

As a result, many regional transportation plans now call for a minimal expansion of the highway system (including no new freeways) but very large-scale investments in mass transit facilities. This is particularly true for newer metropolitan areas, especially those in the western United States, that consist primarily of auto-oriented, low density development that sprawls out over an enormous land area. Despite considerable recent evidence to the contrary, the public and elected officials in most of these cities are convinced that a rail mass transit system is the answer to their congestion and associated auto-generated problems [13].


Nationwide, considerable effort is being devoted to finding ways to generate substantial local funding for new mass rail transit starts and to funding locations for routes and stations in corridors that are usually radial to the traditional CBD of the region. Opinion polls generally show that the public is in favor of building new or additional rail transit facilities (especially when they are not told what they will cost) and most politicians are more than willing to follow their constituents on this issue. Only the shortage of federal funds from the Urban Mass Transportation Administration has limited the number of new rail starts to a relatively small number during the past two decades. This public thirst for more rail transit has not been appreciably diminished by the fact that those rail projects that have been funded and built have generally not performed nearly as well as expected [14].

It is no secret that regional land-use plans are not regarded as likely to have any real impact on developer decision-making activities in the United States. Still, it should be recognized that most cities are evolving toward the polycentric urban form as a result of the interplay of actual real estate market forces [15]. Developer decisions are being influenced by land price variations, highway congestion levels, vacancy rates, permit approval requirements, labor force residential patterns and a host of other factors that jointly impact the manner in which they chose locations for their projects [16]. Land-use plans and policies that call for creation of a polycentric urban form are generally quite consistent with these market forces.

If substantial public investments in rail transit facilities at center locations help attract developers to such locations, they then contribute to the implementation of a centers land-use policy. This is especially true if the building permit review process for center developments is made faster and easier while being made slower and more difficult in locations that are not designated as centers. Further, if developers can be assured that they will meet with little opposition from the community to their development proposals in center areas, they will be even more likely to concentrate their efforts in such areas. Rail mass transit plans that call for connecting these centers with each other add another incentive for choosing a center location rather than developing elsewhere in the region. The joint result of these policies could well be that higher residential and employment densities in these designated centers can be achieved, even though regional and local planners still have only limited authority to implement a centers plan in direct and legally enforceable ways.

Clearly, it is not reasonable to expect all developers to want to do their projects in a location that is a designated center. In the Seattle metropolitan area, regional planners have estimated that only about one-third of the growth over the next 30 years could be expected to occur in the 15 centers that they intend to designate. They also expect that considerable downzoning of areas not designated as centers will be needed to insure that even this growth target is reached. But, if these higher densities can be achieved and if the demand for travel by transit between the centers is large, the mass transit routes that connect them are much more likely to achieve satisfactory patronage levels. These are two big "ifs" but this conventional wisdom is not often questioned [17].

The private sector actors who own the land in the designated center locations usually strongly support these planning concepts and they are normally numerous and politically powerful. Public opinion also appears to find the "cluster-and-connect" concept agreeable. For these reasons, it appears that there is a growing coincidence of the trends defined above. Moreover, there appears to be substantial political support of citizens and developers for the cluster-and connect approach. If the public is willing to pay the rather high infrastructure costs involved, we can expect to see some major urban developmental efforts focus on designated centers during the 1990s and beyond. Some of these centers will also get rail routes and stations during this time frame. If all of this happens, the long-term impact on the urban form may very well be quite substantial.

Given this highly likely scenario of the evolving urban form, we now need to ask if there is an appropriate role in it for PRT. How might PRT be supportive of both a centers land-use plan and a cluster-and-connect radially-oriented rail transit system and therefore become an important component of the region's transit development program!


The centers land-use policy outlined above has several significant weaknesses when one begins to deal with the details of implementing it. And the mass rail transit strategy also has some major weaknesses. PRT can assist materially in overcoming many of these weaknesses if it is deployed properly, giving particular attention to the timing of its construction and the location of its initial segments.

Implementing a centers policy requires coordinated and firm actions by several public and private sector actors [18]. Typically, a regional planning agency will adopt a centers policy and designate those locations (on a map) that are to be treated as centers in the future. Next, local governments have to establish boundary lines for the centers within their jurisdictions and zone the parcels within them appropriately. Local governments will probably also have to downzone other areas within their jurisdictions or find some other way to discourage their growth. Then, they will have to prepare plans that can be used to guide the growth of each center and to find ways to include the infrastructure improvements needed to support this growth in their capital programs. They will also have to find ways to encourage developers to select center locations by streamlining permit approval processes and by helping to gain community support for rapid growth in these locations. Since implementing a centers policy has important tax base implications, some type of taxbase sharing agreement between the units of local government in the region may be necessary to reduce the competition between them for new development. Some special attention may be needed to deal with the activities of speculators who may see land appreciation in the centers area as an attractive opportunity.

Certainly one of the most difficult problems associated with a centers policy is the one that relates to the additional auto traffic congestion that is normally generated by increases in the amount and density of activity within the center. Added to this traffic is the prospect of auto drivers trying to reach and park near the rail transit stations that will be located in or adjacent to the centers. If these problems cannot be solved, then the desired increases in density within the center may not be possible. Typically, it will not be possible to increase the capacity of the roadway system within the center very much if at all (unless large amounts of money are available). Further, it will not normally be possible to provide substantial amounts of parking near or adjacent to the rail transit stations. PRT can assist the solution of both of these problems.

First, it can be used as a circulator for movement within the center. Second, it can serve as a collector/distributor or feeder system to the community surrounding the center. In both cases, it can assist people in reaching the rail stations and other locations in and near the center without using an automobile. Further, it can be easily expanded and extended as the center grows and changes over time. Its capacity and speed attributes particularly are suitable for application in second-level centers which may be expected to eventually contain 30,000-40,000 jobs.

Many second-level centers contain wide streets and are generally quite spacious because of their ample parking areas. This would make it easier to construct a PRT circulator and feeder system as right-of-way problems and adverse construction impacts may be less severe. Serving these two functions well would help keep traffic congestion and air quality problems in check. Developing pedestrian and bicycle environments within the center would also be easier if auto traffic were kept to minimal levels. In these ways, PRT can make a significant contribution to the implementation of a centers land-use policy.

Looking next at the rail mass transit deployment strategy outlined above, one can see at least two major weaknesses. Its stations should be few and far between (to achieve high average speeds) and auto access and parking at these stations areas will generally be difficult or impossible. This means that potential riders will have to walk to a bus stop, wait for a bus, ride to the station, transfer to the rail line and possibly make a second transfer for a bus ride before walking to the workplace or other destination. While PRT cannot eliminate these trip components, it can provide feeder service to rail stations that is quite superior (comfort, convenience, reliability, etc.) to conventional buses running on the existing, usually congested, street system. In fact, it is quite clear that unless a high level of feeder service is provided at all rail stations, the patronage attracted to the rail system is not likely to be high enough to justify its very high costs. It is doubtful that a high enough level of feeder service can be provided by conventional buses running on existing streets.

If the density of the center is increased substantially over time, the growing congestion on its streets and adjacent to its mass transit stations is a problem that will make the bus circulator or shuttle system even more ineffective as time goes on. Since many buses will be using diesel engines, their exhaust emissions make the creation of pleasant pedestrian and bicycle environments within centers difficult and the prospects for improved air quality are also diminished.

The validity of these PRT application ideas rests on the assumption that there is a substantial demand for travel (l) between the various buildings within a center, (2) between the center and its surrounding community, and (3) to/from the rail stations at the center. A recent study has provided some data that shows that there is considerable movement (by car) within suburban activity centers during the normal working day [19].   Studies of the likely demand for travel to the buildings in a center from its surrounding residential areas are scarce but one can reasonably expect that many persons who work at a center live within three miles and could make use of a PRT that extends this far into the area around the center. In a low density urban area, a circle with a radius of three miles will often contain 100,000 people. Clearly, some people in the surrounding area will want to reach the rail transit stations for travel to other connected centers. Studies of all three of these groups are needed to determine what level of travel demand they would generate at different times of the day. Intuitively, it seems likely that the capacity, speed and other performance characteristics of PRT are quite well-matched to serve the mobility needs of all three groups throughout the entire working day as well as on weekends and holidays.

The second weakness is neither a technical nor a functional problem. It is a vitally important political problem. Since most rail transit projects are so costly, a positive vote is required from the largest possible population in order to generate sufficient local tax revenue to fund the system. Since voters often want to trade some direct benefits for their "yes" vote, rail transit proposals are often longer (more extensive geographically) than the few high density patterns a typical metropolitan area can really support. Since most rail proposals involve routes that directly serve the region's CBD, they are often perceived, especially by suburban voters, as not providing much direct short-run benefit to them. Many of these voters make mostly suburban-to-suburban trips and mass transit routes that are radial to the region's CBD have only a limited appeal to them.

PRT can assist in the solution of this problem because it can provide near-term, direct and highly visible benefits to people who have little interest in traveling to the CBD. They are much more interested in being able to reach the suburban centers in the area in which they live. If transit development ballot issues include several PRT systems designed to serve as internal circulators and to/from systems for several outlying activity centers, the voters in these areas (mostly suburban) are more likely to approve the large-scale local funding required to support construction of the radial mass transit facilities that serve primarily the region's CBD. As has been shown recently in Phoenix, a rail transit proposal that does not provide direct benefits to suburban-to-suburban travelers is quite likely to fail. A regional transit development proposal that includes direct benefits to suburban residents in the form of PRT facilities and services is much more likely to succeed at the ballot box.

Figures 7-10 illustrate a base case and three development phases for the suggested PRT deployment strategy for a large metropolitan area. It uses a very simplified, hypothetical metropolitan area as a base. Initially (Figure 7), this area has no rail transit or PRT, just a major freeway system. It has a large downtown and four major activity centers in suburban locations. It also has a large conventional bus system and some freeway flyer service on the radial and circumferential freeway system (not shown in order to keep the diagrams reasonably uncluttered).

Phase 1 (Figure 8) of the transit strategy features the construction of a rail mass transit line between the CBD and the northwest suburban activity center. PRT is used to provide feeder service to all of the rail stations and to provide circulator service within the activity center. PRT circulators are also constructed in the other three activity centers and a PRT feeder is developed for a freeway flyer bus stop on the southern segment of the circumferential freeway. In Phase 2 (Figure 9), a second rail line to a suburban activity center is constructed. Again, PRT feeder systems to its stations are developed and the PRT circulators in all of the suburban centers are extended into the surrounding area. Additional PRT feeders to freeway flyer stops are constructed. In Phase 3 (Figure 10), a third rail line is built and the PRT system is extended further in the suburban area and additional feeder services are constructed for the freeway flyer bus system. A PRT system for circulation within or to/from the regional CBD is not shown as it is assumed to have opted for a high level of rail transit service instead. While this deployment scenario is just one of many that could be described and many important details have been omitted, these diagrams help visualize the essential components and spatial implications of the suggested deployment strategy.

To define some of these ideas in more detail, a PRT circulator system was developed recently in a study at the University of Washington for the Sea-Tac International Airport terminal and its adjacent hotels, long-term parking lots, offiice buildings and other nearby activities [20]. It was determined that a PRT route layout of about 10 miles with 20 stations could be expected to carry some 36,000 travel groups per day and that such a system would have a capital cost of about $70 million. For comparison, the MAX light rail system in Portland, Oregon, is 15 miles long, has 24 stations, and currently carries about 19,000 passengers per day. It cost about $240 million to build and equip [21].


In the 1970s, PRT advocates suggested that PRT be used to replace conventional mass transit as the primary solution to serious and growing urban congestion, energy consumption and air quality problems. The deployment strategy most often suggested called for building the initial PRT system as a CBD circulator and then gradually extending it outward to serve other parts of the region [22]. Not unexpectedly, this strategy did not appeal to those persons who believe that conventional rail is the one and only transit technology that is appropriate for every city. They resisted it strongly, with a wide variety of arguments, and interest in PRT declined to a very low level during the 1980s.

Today, a very different PRT deployment strategy seems more appealing, one that is supportive of a centers land-use plan that is consistent with current market trends and holds some promise as an anti-sprawl, growth management tool. The suggested PRT deployment strategy calls for substantial PRT investments in suburban activity centers during the 1990s, locations that have been designated as "growth centers" as part of a metropolitan-scale land-use plan. Meeting the internal circulation and "to/from" needs of these activity centers, as well as providing much needed feeder service to mass transit stations not located in such centers, appears to be a role that PRT can fill very well during the 1990s and beyond.

The benefits of employing this strategy are likely to be substantial. It would greatly assist the generation of much higher levels of patronage on mass rail transit lines than would otherwise occur, helping to get more cars off the road, thereby reducing gasoline use and air pollution problems. It would also reinforce a centers land-use policy, helping to curb urban sprawl and its many negative fiscal and environmental impacts. Over time, such a strategy would produce a transit capability in the largest urban areas that is much more competitive with the automobile--an attribute that is even more urgently needed now than ever before in our history.

Obviously there are still many automobile-oriented interest groups in the United States that currently see the attainment of such an objective as quite threatening. Strong opposition to any large-scale PRT deployment program from this quarter can be expected. However, one hopes that those interested in the expansion of conventional rail transit investments will see PRT as a necessary ally and lend their considerable support to aiding its deployment in a role that will enhance the utility of their transit technologies. Even if PRT receives enthusiastic support from these interests, it will still be an uphill struggle to achieve the scale of PRT deployment suggested in this article. However, other interest groups, like those interested in improved air quality, reductions in the threat of global warming, conservation of gasoline supplies, reductions in urban congestion levels and the associated costs of delays and many others may eventually see this transit development strategy as being coincident with their objectives. If that time comes, then some progress in efforts to reduce the vulnerability of U.S. metropolitan economies to various environmental and gasoline price/supply threats may begin to be possible. There are only a few good options available. PRT could be an important component in a transit strategy that can be used to deal effectively with problems associated with continuing a heavy dependence on the automobile for meeting metropolitan mobility needs.


1. Jobst Bruggemann, "Cabintaxi PRT GRT SLT", Journal of Advanced Transportation 14:3 (1980): 301-305; and Cabintaxi: Technical Level, Market Situation and Targets, in Personal Rapid Transit III, Dennis Gary, William Garrard and Alain Kornhauser, ed. (Minneapolis: University of Minnesota, 1976); Readers interested in the technical aspects of PRT are referred to J.E. Anderson, "The TAXI 2000 Personal Rapid Transit System," Journal of Advanced Transportation 22:1 (Spring 1988): 1-15; and Technical Committee on PRT of the Advanced Transit Association, "Personal Rapid Transit (PRT): Another Option for Urban Transit," Journal of Advanced Transportation 22:3 (1988). Both sources provide detailed descriptions of the current status of the several components of current PRT technology.

2. J.E. Anderson, Jack Dais, William Garrard and H.L. York, "PRT Planning in the Twin Cities and Duluth," Personal Rapid Transit II, J.E. Anderson and S.H. Romig, eds. (Minneapolis: University of Minnesota, 1974).

3. John F. Kain, "Choosing the Wrong Technology: Or How to Spend Billions and Reduce Transit Use, Journal of Advanced Transportation 21:3 (1988): 197-214; Don Pickrell, Urban Rail Transit Projects: Forecast versus Actual Ridership and Costs (Cambridge, MA: Transportation Systems Center, 1989); U.S. Department of Transportation, Urban Mass Transportation Administration, The Status of the Nation's Local Mass Transportation: Performance and Conditions-Report to Congress (Washington, DC: 1988) p. 240.

4. "Rail Transit Blooms Across the Continent," Progressive Railroading, Annual Mass Transit Issue (August 1990).

5. Victor Gruen, Centers for the Urban Environment Survival of the Cities, (New York: Van Nostrand Reinhold Company, 1973).

6. J. Parr, et al., "City-Size and the Economic Base, Journal of Regional Science ,15:1 (1975): 21-37.

7. J.B. Schneider, 1981, Transit and the Polycentric City, prepared for the Urban Mass Transportation Administration, Report DOT-1-81-33, 294 pp., 1981; R. Cervero, America's Suburban Centers: A Study of the Land Use-Transportation Link, prepared for the Urban Mass Transportation Administration of the U.S. Department of Transportation and the Rice Center, DOT-T-88-14, 1988; and Sandra Rosenbloom, Developing a Comprehensive Service Strategy to Meet a Range of Suburban Travel Needs, prepared for the Urban Mass Transportation Administration, UMTA TX-1 1-0020, 1990.

8. Schneider, Transit and the Polycentric City.

9. J.A. Kieffer, "What are We Going to do about Public Transportation, Journal of Advanced Transportation, 22: 2 (1988): 92-107; Juri Pill, "Emerging Suburban Activity Centers in Metropolitan Toronto, Journal of Advanced Transportation, 17:3 (1983): 301-316; and C. Leinberger and C. Lockwood, "How Business is Reshaping America," Atlantic Monthly ( 1 986): 43-52.

10. Schneider, Transit and the Polycentric City.

11. Municipality of Metropolitan Toronto, Plan for the Urban Structure of Metropolitan Toronto (Ontario, Canada: MTC, Toronto, 1978).

12. Tokyo Metropolitan Government, Second Long-Term Plan for the Tokyo Metropolis (Tokyo, Japan: TMG, 1987) (in English).

13. Kain, "Choosing the Wrong Technology"; Pickrell, Urban Rail Transit Projects; and U.S. Department of Transportation, The Status of the Nation's Local Mass Transportation.

14. Ibid.

15. Leinberger and Lockwood, "How Business is Reshaping America."

16. Schneider, Transit and the Polycentric City; and Transportation Requirements for Urban Activity Centers, Transportation Research Circular #304 (Washington, DC: Transportation Research Board, June 1986).

17. J.B. Schneider, Implementing the Centers Growth Management Concept in the Central Puget Sound Region: Some Policy, Planning and Procedural Issues, Discussion Paper 90-1, Transportation Systems Program, Department of Civil Engineering, University of Washington, Seattle, 1990.

18. Ibid.

19. "Traffic Congestion and Suburban Activity Centers," Transportation Research Circular #359 (Washington, D.C.: National Academy of Sciences/ Engineering, July 1990).

20. Soonman Hong, and J.B. Schneider, The Application of Personal Rapid Transit as a Circulator for the Seattle-Tacoma International Airport, Working Paper 90-1, 'Transportation Systems Program, Department of Civil Engineering, University of Washington, Seattle, 1990.

21. U.S. Department of Transportation, The Status of the Nation's Local Mass Transportation.

22. Anderson et al., "PRT Planning in the Twin Cities and Duluth."

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