Personal Rapid Transit: How Innovation Can Make Transit Self-Supporting

J. Edward Anderson

[Reprinted from GroundSwell, September-October 2006]

The following presentation was given during a panel on "Practical Solutions to Transit Problems" at the annual Council of Georgist Organizations conference held July 20, 2006 at Des Plaines, IL. Moderator was Chuck Metalitz, director of the Henry George School of Chicago, IL. J. Edward Anderson is a Professor of Engineering at the University of Minnesota


In spring 1989 I was informed that during a luncheon attended by a Northeastern Illinois Regional Transportation Authority (RTA) Chairman it was agreed that "We can't solve the problems of transportation in the Chicago area with just more highways and more conventional rail systems. There must be a rocket scientist out there somewhere with a new idea!" The Illinois Legislative Act that established the RTA had given the new agency an obligation to "encourage experimentation in developing new public transportation technology."

The new idea they needed was and is High-Capacity Personal Rapid Transit (HCPRT). A March 2006 European Union Report concludes: "The overall assessment shows vast EU potential of the innovative PRT Transport concept."

In April 1990 the RTA issued a request for proposals for a pair of $1.5 million Phase I PRT design studies. Two firms were selected and after the studies were completed the RTA selected one of the designs for a $40 million Phase II PRT design and test program. Unfortunately, that program was not directly successful, not due to any flaw in the basic concept of High-Capacity PRT, but to institutional factors. There is more and more evidence that HCPRT is an important answer to many urban problems.

Derivation of the New System

It will not be possible to reduce congestion, decrease travel time, or reduce accidents by placing one more system on the streets — the new system must be either elevated or underground. Underground construction is extremely expensive, so the dominant emphasis must be on elevation. This was understood over 100 years ago in the construction of exclusive-guideway rail systems in Boston, New York, Philadelphia, Cleveland, and Chicago. The problem was the size and cost of the elevated structures. We have found that if the units of capacity are distributed in many small units, practical now with automatic control, rather than a few large ones, and by taking advantage of light-weight construction practical today, we can reduce the weight per foot by a factor of at least 20:1. ...

With this finding in mind consider the cost of a fleet of transit vehicles. The cost of the fleet is the cost per unit of capacity multiplied by the capacity needed to move a given number or people per unit of time. The major factor that determines the capacity needed is the average speed. If the average speed could be doubled, the number of vehicles required to move a given number of people would be cut in half. The greatest increase in average speed without increasing other costs is obtained by arranging the system so that every trip is nonstop. The trips can be nonstop if all of the stations are on bypass guideways off the main line.

Off-line Stations are the Key Breakthrough!

  • As just mentioned, because of increased average speed, off-line stations minimize the fleet size and hence the fleet cost.
  • Off-line stations permit high throughput with small vehicles.
  • Off-line stations make the use of small vehicles practical, which permit small guideways, which minimize both guideway cost and visual impact.
  • Off-line stations permit nonstop trips which decrease trip time and increase the comfort of the trip.
  • Off-line stations permit the vehicles to wait at stations when they are not in use instead of having to be in continuous motion as is the case with conventional transit. Thus, it is not necessary to stop operation at night — service will be available at any time of day or night.
  • There is no waiting at all in off-peak hours, and during the busiest periods vehicles are automatically moved to stations of need. Computer simulations show the average wait time will be less than a minute.
  • Stations can be placed closer together than is practical with conventional rail. ... With off-line stations one has both speed and access.
  • Off-line stations can be sized to demand, whereas in conventional rail all stations must be as long as the longest train.
  • All of these benefits of off-line stations lead to lower cost and higher ridership.

The Optimum Configuration

During the 1970s I accumulated a list of 28 criteria for design of a PRT guideway. As chairman of three international conferences on PRT, I was privileged to visit all automated transit work around the world, talk to the developers, and observe over time both the good and the bad features. ...

I compared hanging, side-mounted, and top-mounted vehicles and found ten reasons to prefer top-mounted vehicles (which) ... can accomodate a wheelchair, 3 adults plus fold down seats for small people, riders plus a bicycle, 2 people with luggage, or 2 adults with baby carriage.

Is High Capacity Possible with Small Vehicles?

...In 1973 Urban Mass Transportation Administrator Frank Herringer told Congress that "a high-capacity PRT could carry as many passengers as a rapid rail system for about a quarter the capital cost." The effect of this pronouncement was to ridicule and kill a budding federal HCPRT program. The best that can be said is that PRT was thought to be too good to be true. But PRT was not an idea that would die.

System Features needed to achieve Maximum Throughput Reliably and Safely

The features needed are

1. All weather operation. ...
2. Fast reaction time. ...
3. Fast braking ...
4. Vehicle length ...

These features together result in safe operation at fractional-second headways, and thus maximum throughput of at least three freeway lanes, ie., 6000 vehicles per hour.

During the Phase I PRT Design Study for Chicago, extensive failure modes and effects analysis, hazards analysis, fault-free analysis, and evacuation-and-rescue analysis were done to assure the team that operation of HCPRT would be safe and reliable. The resulting design has a minimum of moving parts, a switch with no moving track parts, and uses dual redundant computers. Combined with redundant power sources, fault-tolerant software, and exclusive guideways, studies show that there will be no more than about one person-hour of delay in ten thousand hours of operation.

How does a Person Use a PRT System?

A patron arriving at a PRT station finds a map of the system in a convenient location with a console below. The patron has purchased a card similar to a long-distance telephone card, slides it into a slot, and selects a destination either by touching the station on the map or punching its number into the console. The memory of the destination is then transferred to the prepaid card and the fare is subtracted. To encourage group riding, we recommend that the fare be charged per vehicle rather than per person. The patron (an individual or a small group) then takes the card to a stanchion in front of the forward-most empty vehicle and slides it into a slot or waves it in front of an electronic reader. This action causes the memory of the destination to be transferred to the chosen vehicle's computer and opens the motor-driven door. Thus no turnstile is needed. The individual or group then enter the vehicle, sit down, and press a "Go" button. The vehicle is then on its way nonstop to the selected destination. In addition to the "Go" button, there will be a "Stop" button that will stop the vehicle at the next station, and an "Emergency" button that will alert a human operator to inquire. If, for example, the person feels sick, the operator can reroute the vehicle to the nearest hospital.


At the present time, mid 2006, all of the technology needed to build HCPRT, including all the control hardware and software, has been developed. All that is needed in the United States is the funds (about $10 million) to build a full-scale test system. Such programs are already underway overseas. HCPRT is a collection of components proven in other industries. The only new thing is the system arrangement. The system control software has been written and excellent software tools are available for final design verification and development of final drawings needed for construction. Because there has been no US federal funding to support the development of HCPRT during the past three decades, few people in the United States have been able to continue to study and develop these systems. The problem is likely the major factor that caused the collapse of the Chicago RTA PRT program. However, thanks to continued efforts of members of the Advanced Transit Association (, there is a sufficient number of people able to lead HCPRT development — it does not take many.

Three PRT systems are currently under development. ULTra ( is being developed at Bristol University in the United Kingdom. The Vectus system is being developed by the Korean steel company Posco ( They announced last fall they would built a test system in Uppsala, Sweden. Microrail ( is one of a family of automated guideway transit systems under development by Megarail Corporation of Dallas, Texas.

Economics of PRT

The Minneapolis light rail system is called the "Hiawatha Line." The newspapers announced that its capital cost was $720,000,000 and that the ridership would be about 20,000 rides per day. That works out to $36,000 per daily trip. Since the annual cost for capital amortization and operation is about 10% of the capital cost and the annual yearly ridership will be roughly 300 times the daily ridership, the annual cost divided by the annual ridership works out to $12 per trip. The average trip length is roughly 6 miles, so the cost per passenger-mile is about $2. This compares with the total cost per mile of an automobile of around 40 to 60 cents.

We laid out and estimated the cost of a PRT system for downtown Minneapolis. It is compared with the Hiawatha light-rail line. Our estimate was about $100 million capital cost and a professional ridership study showed about 73,000 trips per day. Because this system has not yet been built, let's double its cost. Then on the same basis the capital cost per daily trip would be $2740 and the total cost for each trip would be $0.91. On this PRT system the average trip would be about two miles so the cost per passenger-mile or break-even fare would be about $0.46.

What would be the cost per passenger-mile on a built-out PRT system? The cost per passenger-mile on a square-grid PRT system as a function of population density and for values of the fraction of all vehicle trips taken by PRT, called the modal split, is shown to be from 0.1 to 0.7. Several studies suggest that an area-wide PRT system with lines a half mile apart would attract at least 30% of the trips. On this basis, one can estimate the population density needed for a PRT system to break even. Revenue will be obtained not only from passenger trips, but from goods movement and advertising as well — roughly half is a reasonable estimate, meaning that a passenger would have to pay only half the amount determined. For example, if the population density is 6000 persons per square mile (Chicago density is about 13,000 people per square mile) and the mode split to PRT is 30%, the total cost per passenger-mile is about 40 cents, of which the passengers would pay about 20 cents.

Land savings

In over 90% of the autos there is only one person, occasionally two, and very occasionally three (on a freeway running at capacity which is about 6000 autos per hour on a 3-lane freeway with the 4th lane just an acceleration lane.) A typical freeway width from fence line to fence line is about 300 feet. The two PRT lines in the middle take up only 15 feet of width, giving a width reduction per unit of capacity of 20:1 or 5% of the land area. But, land for a PRT system is required only for posts and stations, which is 0.02% of the land area. The auto requires about 30% of the land in residential areas and roughly 50% to 70% of the land in downtown areas. The enormous land savings permits development of safe, low-pollution, energy-efficient, quiet, environmentally friendly, high-density living.

Energy Savings

Minimum energy use requires very light-weight vehicles; smooth, stiff tires for low road resistance; streamlining for low air drag; and efficient propulsion, all of which can be designed into a PRT system if the designer wishes to do so. Moreover, unlike conventional transit, in which the vehicles must run to provide service whether anyone is riding or not, PRT vehicles need run only when people wish to travel.

Comparing energy use per passenger-mile of eight modes of urban transportation — heavy rail, light rail, trolley bus, motor bus, van pool, dial-a-bus, auto and PRT — PRT would be more than twice as energy efficient as the auto system, which in turn is almost twice as energy efficient as the average light rail system.

Benefits for the Riding Public

* The system will be easy for everyone to use. No driver's license needed.
* The vehicles wait for people, rather than people for vehicles.
* The trip cost will be competitive.
* The trip will be short, predictable, and nonstop.
* There will be minimum or no waiting.
* Everyone will have a seat.
* The system will always be available at any hour.
* The vehicles will be heated, ventilated, and air conditioned.
* There will be no crowding.
* There will be no vehicle-to-vehicle transfers within the system.
* The ride will be private and quiet.
* The chance of injury will be extremely remote.
* Personal security will be high.
* The ride will be comfortable.
* There will be space for luggage, a wheelchair, a baby carriage, or a bicycle.

Benefits for the Community

  • The energy use will be very low.
  • PRT can use renewable energy.
  • Deployment of PRT will reduce transit subsidies.
  • PRT can augment and increase ridership on existing rail systems.
  • PRT will be attractive to many auto users, thus reducing congestion.
  • Seniors, currently marooned, will have much needed mobility and independence.
  • The system does not directly pollute the air. Being more energy efficient than the auto system and by using renewable energy, total air pollution will be reduced substantially.
  • By spreading the service among many lines and stations, there will be no significant targets for terrorists.
  • As to accidents, no one can say there will never be an accident, but the rate per hundred-million miles of travel will be less than one millionth of that experienced with autos.
  • There will be huge land saving: 0.02% is required vs. 30-70% for the auto system.
  • PRT will permit development of more livable high-density communities.
  • The ride will be pleasant for commuting employees, thus permitting them to arrive at work rested and relaxed.
  • PRT will permit more people-attracting parks and gardens.
  • PRT will permit safe, swift movement of mail, goods and waste.
  • PRT will provide easier access to stores, clinics, offices and schools.
  • PRT will provide faster all-weather, inside-to-inside transportation
  • PRT will enable more efficient use of urban land.
  • By making the inner city more attractive, urban sprawl will be less likely.

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