Thirty Five Frequently Asked Questions About the Taxi 2000 Personal Rapid Transit System Version 1.0, July, 1994 by J. Edward Anderson, President and CEO of Taxi 2000 Corporation (with permission). The Raytheon Company recently purchased the rights to the TAXI 2000 technology and is now developing their own version of PRT, using Professor Anderson's previous work to guide their efforts. Raytheon hopes to have a test track and three vehicles up and running in 1995 in Sudbury, Massachusetts. This development and testing activity is Phase II of a joint project with the Regional Transportation Authority in Chicago, Ill. (serving primarily the suburbs in the Chicago metropolitan area). Phase III involves building and operating a small PRT system in Rosemont, Ill. (located near O'Hare International Airport). 1. Is PRT "reinventing the automobile?" No! PRT is a public transit system. It cannot replace the automobile, but its service characteristics are such that it can be expected to attract many more people than conventional transit systems, and it can do so using a tiny fraction of the land required for the automobile. While roughly half the population either cannot or should not be driving automobiles, Taxi 200 is accessible to everyone. It will be the environmentalist's dream because of its markedly improved energy efficiency, lack of air pollution, and land savings. We normally recommend guideways spaced not less than a quarter to a half mile apart. They do not replace streets. The lead article of the July 1969 issues of Scientific American is still a most useful introduction to PRT and its profound differences from today's means of urban transportation. 2. Can small cars move the large numbers of people who would use general mass transit? Today, automobiles averaging 1.5 people per vehicle carry more than 97 percent of the urban passenger-miles in the United States. Uninterrupted flow is the key to capacity, not vehicle size. As an example, 60-passenger buses coming two minutes apart, a very high flow rate for an American bus system, provide the same number of capacity units per hour as 3-passenger PRT vehicles coming every six seconds. One Taxi 2000 line can serve more than six times this capacity, more passengers per hour than come into downtown Boston during the morning rush period via a three-lane highway bridge that merges U.S. Highway 1 and I-93 traffic. The line capacity of Taxi 2000 is high because of automatic control, an in- vehicle switch, and electromagnetic propulsion and braking. Automatic control is safer and more reliable than human drivers, permitting vehicles to be separated by small distances. In-vehicle switches work faster and more reliably than moving-track switches, again permitting vehicles to be closely spaced on the guideway. Linear electromagnetic braking is reliable in wet and icy weather that forces systems using rotary motors and wheel braking to spread vehicles far apart because of skidding concerns in emergency stops. 3. Won't stations get bogged down with all the small vehicles? Station throughput is determined by the number of station berths, which can be set to meet the demand of any particular station. In general, station throughput is high relative to conventional mass transit because: * Only vehicles that actually need to stop at a station will enter the station. All other vehicles pass by, thus reducing station traffic relative to conventional systems where all vehicles stop in each station regardless of where passengers are going. * PRT stations are closely spaced, often within a quarter mile of each other. This is convenient to patrons, who walk only short distances, and results in smaller, less crowded stations. * The loading time for each vehicle is relatively short, often completed in less than five seconds. As people become accustomed to PRT systems, they will enter and exit vehicles as quickly as cars, increasing station throughput and minimizing trip time. 4. Won't the problems of reliability make the operation of a large fleet of small vehicles undependable? Actually, because a PRT system will have a large number of small vehicles, rather than a relatively small number of large vehicles, your chances of becoming involved in a failure will reduce in proportion to vehicle size if the reliability of each vehicle is the same. But, because of the use of checked redundancy and advanced failure-management strategies possible within the confines of a PRT system, and the benign environment within a vehicle, Taxi 2000 will be substantially more reliable than a conventional transit system. It has been shown that the requirements for dependability in a PRT system are independent of system size. 5. What happens if a PRT vehicle stops on an elevated guideway between stations? Questions of reliability, safety, evacuation and rescue are fundamental to the design of any elevated transit system including PRT. Each Taxi 2000 vehicle has two motors and two controllers, modern failure-monitoring systems, fault- tolerance and fail-safe features. The system has alternative power sources so that a power failure will not leave passengers stranded. There are roughly 50 elevated automated transit systems operating in the world today that prove that a vehicle stopping when not intended is a very rare event. If a vehicle does stop between stations, Central Control will talk with the passengers through an intercom system and guide the rescue operation. The vehicle behind will soft engage and push the disabled vehicle to the nearest station. In the very unlikely event that the vehicle can't be moved, a rescue team will come with a ladder and help the passengers out of the vehicle. 6. What if there is a power failure? Taxi 2000 vehicles receive their power from 600-volt DC power rails located inside the guideway. There will always be an alternative power source. One way is to power the system from gas turbine-generator sets and to use utility power as emergency backup. Another way, depending on circumstances, is to power the vehicles from wayside batteries, which can be charged at night when the power rate is low. During a municipal power failure, vehicles would still receive battery power, so they would simply slow down to conserve energy, finish their trips, and strand no passengers. 7. What if a truck hits a post? If the guideway runs down the center of an arterial street or on the edge of such a street, highway barriers can be placed on concrete pedestals so that it is not possible for vehicles to hit the posts. The posts are, however, substantial enough so that it would take a high speed collision of a large truck to shear off a post. If a post were sheared, the guideway will remain intact and the vehicles will remain in the guideway. 8. Will the visual impact of PRT be acceptable? Visual impact is important in all transit systems. Many rail transit systems are placed underground because a ground-level system requires destruction of too much existing property and an elevated system is too massive and noisy. A Taxi 2000 guideway has less than five percent of the cross sectional area of a rapid rail system, will generate almost no noise, and has an external appearance that can be varied to suit any specific community. According to one famous sculptor, Taxi 2000 adds excitement and grandeur to the urban scene, both for what it is and what it does. People accept elevated structures if they see them as a practical means to a desired end. In the early 1970s, when conventional heavy rail systems were being promoted, officials argued that elevated structures were acceptable. The Downtown People Movers proposed in the late 1970s had massive structures (witness the Detroit and Miami People Movers) but local authorities considered them acceptable because they were believed to fulfill a need. Taxi 2000 will have much smaller visual impact and will provide much better service at lower cost. 9. How does a person use Taxi 2000? At each station, there will be several conveniently located ticket machines and a map of the system. The patron, or small group of patrons who want to ride together, determine their destination number from the map and go to the ticket machine to punch in the destination. The machine verifies the destination and displays the fare, which may be paid by cash or by prepaid tickets and is per vehicle rather than per person. The machine then dispenses a magnetically coded ticket. The patron takes the ticket to a stanchion in front of the first empty vehicle in a line of vehicles and inserts it into a slot. This act transfers the memory of the destination to a microprocessor on board the vehicle, causes the door to open, and assures the patron that he or she is getting on a vehicle headed to his or her station. The patron walks into the vehicle, sits down and presses a go-button, whereupon the door closes automatically, the control system waits for an opening in the traffic bypassing the station and commands the vehicle to accelerate to line speed. When the vehicle reaches the destination station, it pulls into a berth and the door opens automatically. The patron exits the vehicle and leaves the station. If the patron is regularly going between a certain station pair, he or she can purchase a pass in advance, bypass the ticket machine and go directly to the stanchion in front of the first empty vehicle. Taxi 2000 doesn't need turnstiles since a valid ticket is necessary to gain access to a vehicle. 10. Is it possible to stop before the end of the ordered trip? Yes. Each vehicle contains a stop button, which if pressed stops the vehicle at the next station. 11. What about access for the handicapped? Taxi 2000 will be fully accessible to handicapped patrons and will comply with the Americans with Disabilities Act. Elevators will be provided in elevated stations and the ticket machines and stanchions will include intercoms and Braille plaques to insure ease of use by all patrons. The vehicle accommodates wheelchairs easily, with an open seat for one traveling companion. The platform is level with the vehicle floor to prevent wheelchair bumps and is textured at the edge to assist the blind. Taxi 2000 is designed to be easily accessible to all people, whether handicapped, young, old, carrying heavy bags, traveling with a bicycle, or having any other special need. It has been praised and promoted by groups representing the needs of the handicapped. 12. How much time does a person have to board a PRT vehicle? As much time as is necessary. The vehicle will not move until the passengers have entered and the door is closed and locked. Loading or unloading time is a statistical variable, which varies from a minimum of about two seconds to a maximum of 15 to 20 seconds. 13. Will you have to ride with strangers? No! Taxi 2000 is a Personal Rapid Transit system. Each vehicle is occupied by passengers riding alone or together by choice. If someone tries to force his way into a vehicle, a button can be pushed inside the vehicle to alert the police. 14. Can a PRT vehicle be entered from either side? Yes. It is not in general practical to design a PRT network in such a way that all stations are on one side of the guideway. Therefore the cars are designed with doors on both sides, but only the door on the station side opens when the vehicle stops. 15. How serious a problem is vandalism? In Taxi 2000, vandalism is minimized in the following ways: By Surveillance. The stations will be television monitored with two-way voice communication. They are small areas that can be surveyed easily, and infrared detectors will be used to detect the presence of people so that the operator, in slack times, need not constantly view the screen. By Identification. a means will be provided to permit a boarding passenger to reject a vandalized vehicle. An alarm signal will then be sent to the nearest control room where a human operator is alerted to roll back a video memory unit and make a permanent record of the last passenger to egress from the vandalized vehicle, and to command the vehicle to the nearest maintenance shop. Normal police methods will then be used to apprehend the vandal. Experience at the Morgantown automated people mover system has shown that knowledge of such a procedure, not possible in conventional transit, will by itself deter most vandals. By Psychology. In public places, vandalism has been greatly reduced by the application of human psychology (see Psychology Today, September 1982). Plain walls that look like writing tablets invited being written on. Textured walls and walls with diagonal lines or protrusions markedly reduce graffiti. Appropriate colors, music, architectural design, and plants reduce vandalism. Frequently cleaned public places are not as subject to vandalism as dirty ones. By use of Attendants. In large stations or in stations unusually prone to vandalism it is not economically unreasonable to use attendants, and they may be used if other methods fail. 16. Won't personal security be a serious problem in PRT? Personal security is less of a problem than in conventional mass transit, and even sometimes less than in automobiles, for the following reasons: * The ride is nonstop, direct to the destination, and alone or with one or two other people of choice. One never needs to ride with strangers. * Computer simulations have shown that in a well-designed system in the rush period about 60 percent of the passengers will wait less than 30 seconds and 90 percent less than three minutes. During off-peak periods there is no waiting at all. Thus, there is little time for commission of acts of aggression. * Television monitors and two-way voice-communication systems will be placed in the stations to survey the platform, stairways and vehicles. To insure that the screens will be watched, infrared sensors will be placed in the stations to alert the monitoring personnel of activity in each station. * The station platform is typically no longer than 20 to 40 feet and about 12 feet wide, and is easy to watch - much easier than a large, multi-story parking structure. Care in station design will eliminate areas in which a potential assailant can hide. * A stop button in the vehicle permits the passenger to order the vehicle to stop at the next station for any reason. * A voice communications system will be installed in each vehicle to be used to call for help in any emergency. 17. Won't the issues of safety make it difficult to insure a PRT system? The insurance rate for the first operational Taxi 2000 system will be based on the insurer's estimate of the frequency and severity of bodily injury sustained while riding, attending to, or being in proximity of the system. In today's litigious society, it would not do to rush such a system to completion and to permit the public to ride before it was thoroughly tested. Every reasonable practical precaution must be taken in the design of the new PRT system to assure safety, and there will be an adequate period of testing before opening the system for public use. An extensive series of design features are incorporated into Taxi 2000 both to minimize the probability of failures that may cause injury, and to minimize the consequences of any failure. A remarkable characteristic of PRT is that, because the vehicles are small and light, it is practical to design to assure that no combination of failures can cause injury. The developers of Taxi 2000 believe that its system will provide a substantial improvement in both safety and personal security. Obtaining a reasonable insurance rate for a Taxi 2000 systems depends not only on the design features but also on the program of development and testing undertaken before the public can ride. Before building a demonstration for public use, a half-mile oval test system with one off-line station and four prototype vehicles will be tested. Based on the results of the test program, the first real people-moving demonstration will be constructed, tested, and certified for public use before the public will be permitted to ride. Potential insurers will be invited to monitor the test program in sufficient detail to establish the insurance rate. 18. Isn't there an economy of scale in transit systems, i.e., to carry a given traffic level, won't a system of many small vehicles cost more than a system of a few large vehicles? The basic features of PRT follow logically as features that minimize the total cost per passenger-mile. These features permit true minimization of guideway cost, vehicle-fleet cost, and operating cost while maximizing service. * Data shows that transit vehicles cost about the same per unit of capacity no matter how large or small they are. Contrary to intuition, there is no economy of scale. By using nonstop trips, possible with off-line stations, the average trip time of a PRT system is two to three times less than in a conventional transit system, which means that the fleet capacity (number of vehicles W capacity per vehicle), and therefore fleet cost needed to serve a given number of trips, is less by the same factor. * Vehicles of the size required to hold up to three seated adults have a much smaller cross section and weigh substantially less per unit of length than large standing passenger vehicles, and, because of much lower dynamic loading, lead to lower guideway weight (15 times lower) and lower cost. * To compare operating and maintenance (O&M) costs, we define a quantity called a "place-mile". The number of place-miles of travel in a transit system consisting of vehicles or trains of any size is the number of vehicle- miles of travel multiplied by vehicle capacity. A vehicle-mile is one vehicle traveling one mile. Because PRT vehicles move only when service is demanded, the total number of place-miles per day required to serve a given level of passenger demand is only about a third as much as in a conventional scheduled transit system. Examination of data on O&M costs shows that the O&M cost per place-mile is nearly the same regardless of the type of transit system. Thus the O&M cost of a transit system that carries a given number of people per day is proportional to the number of place-miles per day of travel. The remarkable result of this kind of systems-economic analysis is a transit system in which the features required to minimize both capital and operating costs are exactly those that provide maximum service, i.e., on- demand, alone or with one or two friends, in seated comfort, any time of day or night, at a predictable average speed two to three times that possible with conventional transit. The only reason for using large vehicles in urban transportation is to amortize the wages of drivers over as many fare-paying riders as possible. Automation permits relaxation of system characteristics toward a true optimum. 19. How much will a ride cost? Transit fares are normally set as a matter of public policy, and are as high as the public will bear without significantly reducing ridership. In most conventional systems, the fare covers only about 30 percent of the operating costs and capital cost is never recovered. Thus, present transit systems require large state and federal subsidies. Because of its low capital and operating costs, Taxi 2000 systems will charge fares that are comparable to conventional mass transit, yet will require little or no subsidy. This will permit systems to be installed in communities that need transit but don't have access to large state and federal subsidies. 20. Why three-passenger vehicles? On a strictly economic basis, one-person vehicles minimize capital costs, but they do not serve obvious social needs. Two-person vehicles are too small for a small family, for taking luggage, or for a wheelchair plus attendant. Also, if a party of three wants to travel together, one of them would have to ride alone if the vehicles hold only two persons, which may be socially awkward. So the vehicle should have at least three seats side-by-side. If, on the other hand, four-seat vehicles are specified, designers try to reduce cost by placing two back seats forward and two forward seats backward in a socially pleasant and minimum-cost configuration. Such a vehicle is, however, longer by the length of a seated person, which increases station length and cost. From the viewpoint of ultimate safety, a passenger can be protected in a sudden stop if he or she is behind a padded dashboard. The above four- passenger configuration has a much longer throw distance and therefore greater probability of injury in the unlikely event of a sudden stop. Also, about 95 percent of the trips in an urban area are taken by one, two, or three persons traveling together, so a system of four-passenger vehicles results in more dead weight of vehicle per person carried and higher capital and energy cost. We see that the factors that must be considered in picking vehicle capacity are not the same in PRT as in a family automobile. A PRT trip is generally quite short and a group larger than three can fit into two vehicles, which leave the origin station seconds apart and arrive at the destination seconds apart. Taxi 2000 is designed to carry a total load of 750 pounds. It can hold a family of four on a 57 inch wide bench seat if the total weight is less than 750 pounds. 21. Why are the vehicles mounted above the guideway rather than below? There are several reasons: 1) There must be a certain clearance for trucks to pass below. If the vehicles hang, the guideway must be seven or eight feet higher than if the guideway is below the vehicles. Also, with hanging vehicles, the posts must be along the side of the vehicles and cantilevered at the top. Wind load is one of the major loads on the system. The combination of wind load and cantilevered vehicle load gives a bending moment at the foundation about twice as high with hanging vehicles as with vehicles supported from below, thus the foundation must be twice as large with hanging vehicles. 2) The cantilevered guideway mount cannot provide as rigid a connection to the support post as a bottom-mounted system in which the guideway is rigidly connected to the posts by means of a moment-carrying bracket. Thus, if the two systems are to have the same ride comfort, the guideway of a hanging-vehicle system will have to be stiffer and more costly. 3) Switching wheeled hanging vehicles requires that the wheels pass over the slot in the guideway required for the vehicle's support rods. This has always been a difficult problem. 4) We believe a majority of people would prefer to have the comfort of seeing the guideway beneath them. 22. Why are the moving switch parts in the vehicle rather than in the guideway? There are five reasons an in-vehicle switch is superior to a moving-track switch. Reliability. The simplicity of the in-vehicle switch makes it inherently more reliable than the in-track switch, and an in-vehicle switch can easily be made bi-stable by means of a spring. The worst that can happen with a well-designed in-vehicle switch is that one small vehicle will be misdirected, whereas if an in-track switch fails, it ties up a whole line of traffic, thus delaying many people. The result is that the required reliability is far beyond that needed in PRT if the switch is in the track, but is easily attained if the switch is in the vehicle. Capacity. Because of the time required: 1) to move an in-track switch, 2) to verify that it is locked in position, and 3) to be able to stop before the vehicle reaches the switch if verification is not obtained, the minimum time headway will be too long to be of use in a PRT system. An in-vehicle switch completely removes this barrier to high capacity. Ride Comfort. In-track switches often consist of a series of articulated straight pieces of guideway that swing back and forth. Passengers will feel such a strong lateral jerk each time the vehicle passes one of the joints that the vehicle will have to slow down for every passage, and there can be four or five straight pieces in each switch. An in-vehicle switch permits guideway branch points to be made with simple smooth curves, maximizing passenger comfort and minimizing jerk loads on the undercarriage of the vehicle. Visual Impact. Articulated in-track switches increase the visual impact of a switch section greatly. Beyond simply being much larger than a simple branch section, in-track switches have a track leading into empty space, which is discomforting to view for passengers as well as passers by. Cost. The Taxi 2000 patented in-vehicle switch has very few moving parts and is very simple and inexpensive to build. An in-track switch is much larger, often consisting of several articulated track sections that move back and forth, and contains many large parts which increase cost significantly. 23. Are one-way guideways practical? Because of Taxi 2000's very small guideway and in-vehicle switching, one- way guideways are an option, but not a necessity. If the guideways are one- way, for a given investment, twice as much land area can be placed within walking distance of stations as with two-way systems. If planners want two- way systems, they are easily provided. We have analyzed the problem of extra trip circuitry with one-way guideways and find that, with a reasonable layout, the extra travel time going nonstop from origin to destination is so small that the cost per passenger-mile is most often less with a one-way system. 24. Will magnetic levitation help PRT? Not at urban speeds. Comparisons of systems levitated by magnetic fields, air cushions, and wheels show that, by using low rolling resistance tires, there is no advantage of either magnetic or air suspension over wheels at urban speeds, and indeed several serious disadvantages. 25. Where are vehicles stored when not in use? In an n-berth station, n vehicles can be stored when there is no demand for service. During the night when demand is low or zero, the bulk of the vehicles will be stored at special storage barns strategically located in the network, usually at the same locations as cleaning and routine maintenance facilities. Because it is not necessary to get a specific vehicle out of storage before the others, the volume of storage facilities per mile of guideway is usually not more than would be required to store about four or five automobiles in a multi- story parking structure. 26. What will be the cruising speed? The first demonstration of Taxi 2000 will have a maximum cruising speed of 30 mph because this is sufficient in major activity centers. To span metropolitan distances, higher speeds are necessary, and the cruising speed is determined by ride comfort and motor power. Taxi 2000 has been designed so that growth to speeds in the range of 50 to 60 mph appear practical. 27. How is ride comfort assured? Taxi 2000 differs from other automated guideway transit systems in that the running surfaces are adjustable with respect to the basic guideway frame, which is built to normal structural tolerances. Before service is started, ride comfort is tested, adjustments are made and the running surfaces are firmly bolted in place. (In other systems, it is virtually impossible to correct any misalignment once the guideway is installed.) The vehicles run on smooth synthetic rubber tires of stiffness needed to meet ride comfort criteria. Since the running surfaces are smooth and adjustable, secondary suspension is not needed. 28. How do we keep snow, ice or debris from interfering with operations? The Taxi 2000 guideway is a truss structure with covers over the sides and part of the top and bottom. There is a six inch wide slot at the top for the vehicle's vertical chassis to pass through, and an eight inch slot at the bottom to permit ice, snow, rain, or debris to fall through. A pair of seven and a half inch wide running surfaces (angle sections) inside the guideway near the bottom support the main wheels and are spaced six inches apart to permit anything that may drop in the top to pass through. Running vehicles continuously during snow or ice storms will usually be sufficient to clear the running surfaces; but we have designed and tested a plow that, if necessary, will be installed on vehicles to deflect anything that lands on one of the running surfaces and falls down into the slot below. A maintenance vehicle will occasionally inspect the interior of the guideway with a television camera and will be equipped to remove any foreign material. 29. What about energy use? Because of frequent stopping and starting, about two thirds of the operation energy used by today's transit vehicles or automobiles in an urban area is kinetic energy lost in heat as the vehicle is braked to a stop. Therefore, elimination of the intermediate stops by itself almost triples energy efficiency. Careful attention to vehicle weight minimization, streamlining, lowering of road resistance by careful selection of tire parameters, and use of electric propulsion that eliminates idling energy add to efficiency and put PRT in a class by itself in terms of energy efficiency. The electrical energy use will be about 150 watt hours per vehicle-mile. The power will peak at about 20 kw per vehicle and will average about 4 kw per vehicle. 30. What about air pollution? Taxi 2000 vehicles run on 600 volt DC electricity that can be supplied from wayside batteries that can be charged by any electrical energy source including renewable energy such as wind, solar, or biomass. Thus the system produces air pollution only in the processes of manufacture and at the power plant, both of which can be closely controlled. 31. How quiet is the operation of a PRT vehicle? Movement of Taxi 2000 vehicles will be much quieter than automobiles. They are propelled and braked through linear induction motors, which are driven by variable-frequency drives. Such drives may produce a humming sound, which is minimized by careful design and by sound insulation. Since there is no braking or traction through the wheels, the tires are smooth and they run on smooth surfaces, so the tire noise will be substantially less than produced by an automobile. There are no other noise-producing elements. 32. Will the use of electric and magnetic components adversely affect the health of riders? Because Taxi 2000 vehicles weigh a small fraction of conventional rail transit vehicles, the electric current required is correspondingly less and any magnetic field in the cabin will be proportional to the current. While there are at present no generally accepted safety standards that limit human exposure to magnetic fields, care has been exercised in the design of the Taxi 2000 vehicles to minimize the exposure of passengers to AC magnetic fields. Taxi 2000 motors are designed to constrain the magnetic fields to their immediate vicinity and are located remotely from the passenger compartment, which also desirably lowers the center of gravity of the vehicle. Residents living or working near a Taxi 2000 guideway will not be exposed to any significant increase in AC magnetic fields since the power to the vehicles is provided from 600 volt DC power rails inside the guideway. Harmful effects of DC transmission lines have been reported only when the lines carry several hundred thousand volts. 33. Will PRT guideways withstand earthquakes and high winds? The Taxi 2000 elevated guideway is designed to the local code for maximum accelerations during earthquakes and the maximum expected wind load. The guideway is a small, lightweight, flexible, steel structure with thermal expansion joints in every span, a configuration well suited to surviving earthquakes and high winds. The possibility of aeroelastic coupling such as that which caused the collapse of the Tacoma Narrows bridge has been studied, and it was found that features that prevent such catastrophes are exactly those selected for the Taxi 2000 guideway for other reasons. 34. Why has it taken so long to get true PRT into operation? The PRT concept germinated in the early 1950s and received enough attention by the mid 1060s to be the subject of government-funded analyses. By the early 1970s, there were many competing ideas on how to design automated transit systems, but there was no theory of PRT and there were insufficient funds to explore the dozens of alternative design features. This "Tower of Babel" discouraged decision makers, caused government funding to dry up, and left the continued search for an optimum configuration up to a few people. A major reason it was possible in the 1980s to carry PRT research and development far enough to regain the attention of major transit decision makers was emergence of the personal computer and associated software. Finding the optimum transit configuration and proving it required sophisticated and data- intensive engineering and economic calculations, detailed simulations of control and vehicle dynamics, and a great deal of data processing, which during the 1970s was much slower and required large resources, generally funded only by governments. The PC enabled engineers of ordinary means to purchase enough computer power to develop the optimum system and element designs. In parallel, the development of powerful fault-tolerant microprocessors and software elements have placed the control requirements of PRT well within the current state-of-the-art. While many new ideas have emerged from institutional research during this century, new ideas in previous centuries generally emerged only when the individuals who discovered and developed them could do so without anyone else' approval. Development of PRT required understanding of engineering sciences and sophisticated technology of the 20th century melded with the individuals initiative of earlier centuries, a marriage made possible by the low- cost, high-performance personal computer. The PC and the microcomputer, coupled with the development of the necessary transit systems theory, test and operational experience with a wide variety of automated transit systems, the realization that conventional rail transit systems cannot solve the problems of congestion in cities, and the steady worsening of congestion and air pollution have made it possible for the idea of PRT to reemerge. Careful research over decades has shown no flaw that will or should stop the development of PRT, but rather that PRT is a badly needed solution to a variety of transit problems. It is a new configuration of now very ordinary parts well within the current state-of-the-art. Development of new concepts in public transportation differs from development of many other emerging concepts in that the resources needed to prove a concept are large, many people are involved in deciding to take a positive step, the level of credibility must be unusually high, and the "fear factor" that drove military programs is not present. In such circumstances, it is not surprising that several decades have been required to bring the concept of PRT to maturity. 35. When? This has been the one real concern about PRT. We have been fortunate to be able to continue to work with a growing number of colleagues and organizations, and are finding interest in more and more cities and countries. We are confident that PRT will be a reality in a few years. The possibilities are exciting. Many people have given of their free time because they have seen in Taxi 2000 a means for a profound improvement in the functioning of urban areas. Those willing to listen, study and compare are seeing that in greater and greater numbers. A critical mass of interest is developing. -Jerry Schneider .