The Get On Board! PRT

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Topics / Selections / History


by Bill Wilde

to "Personal Rapid Transit — Cyberspace Dream Keeps Colliding With Reality," Light Rail Now! Publication Team, March 2004

This article is a wonderful contribution to the PRT debate. In one place the critics have given it their best shot. Henceforth when one needs to present the case against PRT this single reference will suffice. Nobody’s ever done it better, or is likely to.

One of the first questions about the article is its authorship. Who wrote it? Who is on the team that approved it? Why don’t their names appear under the title?

The team doth protest too much, methinks. One wonders why. Why does the elephant fear the mouse? According to the 2002 National Transit Database, U.S. transit spent $36.5 billion in capital and operating funds in 2002. Taxi 2000 Corporation is seeking $24 million to fund a multi-year Product Certification Facility (PCF), less than seven one-hundredths of one percent of this amount. Development funding is being sought from private and public investors. Is this meager amount such a threat to the established interests? Especially since the team concludes that PRT is wholly impractical, is fundamentally flawed, and could never work. Why fear that which could never hurt you?

In discussing PRT, the parties must begin by agreeing on what PRT is and what it is not. This has confused the debate for decades. The Advanced Transit Association defines PRT as having the following characteristics:

• Fully automated vehicles (i.e. without human drivers)
• Vehicles captive to the guideway, which is reserved for the vehicles
• Small vehicles available for exclusive use by an individual or a small group traveling together by choice, all seated.
• Small guideways that can be located above ground, at ground level, or underground.
• Vehicles able to use all guideways and stations on a fully connected PRT -network.
• Direct origin to destination service, without a necessity to transfer or stop at intervening stations (i.e., non-stop service).
• Service available on demand rather than on fixed schedules.

This definition is consistent with that in U.S. Congressional Office of Technology Assessment’s "Automated Guideway Transit" report of1975. Thus when the article discusses "the AirTrans system at Dallas-Ft.Worth Regional Airport, and the PRT at West Virginia University at Morgantown" it refers to Group Rapid Transit and not PRT. All references to these systems in the article are irrelevant. Unfortunately the name PRT has been applied to many systems over the years that are not PRT. The fact is that genuine PRT has never been operated in revenue service.

Chicago Transit Authority’s PRT effort began as an honest exercise. From the outset PRT was defined properly and adhered to. Unfortunately Raytheon scrapped the Taxi 2000 design that won the competition and substituted its own design without visible rational basis. Although Raytheon by contract attempted to design and build the right thing, true PRT, their execution was deeply flawed. The result was a very heavy vehicle, a large and visually intrusive guideway, propulsion and braking unsuitable for short headway operation, and consequent cost estimates that subsequently killed the program. This was indeed a disappointing outcome for an initially promising effort. The lesson is simple and timeless — a thing can be done well or poorly.

When discussing design aspects of PRT the article reveals a serious lack of research. The first criticism is the visual impact of elevated guideways. This is a subject that can be debated theoretically but in fact the public’s reaction and acceptance cannot be known until true PRT is operating somewhere. A proper judgment can only be made in the context of PRT’s utility and in relation to the alternatives. In a vacuum the public would never accept massive freeways through cities, acres of asphalt parking, congested streets, enormous energy usage, emissions, accidents, and very high private and public costs. These attributes of our most popular urban mode are accepted only because the public knows the utility of automobiles from daily personal experience. The public would not accept noisy 40-foot transit buses without some idea of their limited utility. Only after PRT is operating somewhere can informed judgments be made. And, as with any automated system, guideways can be located above ground, at-grade, or underground as desired as long as vehicles have exclusive use. If critics are convinced that PRT would never be accepted visually, why do they fear its development?

The article fears that "Snow and ice accumulation, rain, and otherconditions can affect or interrupt service" and wonders "How would passengers extricate themselves from their little cars and guideways?" The design of a leading PRT system, Skyweb Express, has addressed these issues extensively. The proof of the design’s weather tolerance will be demonstrated at the PCF. Well-meaning regulators may require walkways alongside the PRT guideways until their need is refuted in actual service. Extensive analysis of dealing safely with failed vehicles has shown that walkways are not an optimal solution. The critics show no evidence of knowledge of this analysis. If they are convinced that this is a fatal flaw of PRT, why do they fear it so?

The fear of "system droppings" also reflects a lack of understanding of the Skyweb Express design. The vehicle chassis is a very simple machine with very little that would produce "droppings" and the guideway is mostly enclosed on the underside.

In criticizing PRT station size the team obviously is unfamiliar with the Skyweb Express design. An elevator is included and the station is ADA compliant. The PRT system offers a whole new world of convenient mobility to disabled persons. Why would PRT critics not even allow the demonstration of this capability? What do they fear?

In speculating about a PRT station not being able to accommodate "the massing of large numbers of passengers" the critics fail to grasp the fundamental nature of PRT. Passengers are not massed awaiting the scheduled arrival of a massive conventional transit vehicle. Passengers depart with little or no wait. They flow through the station as opposed to gathering in bunches to meet the needs of old technology. If the system is so popular that station capacity becomes an issue, then more stations can be added without impacting service to others on the system. Indeed, as with all transit, having too many customers is a happy problem, much more easily dealt with by PRT than by conventional modes.

The whole section titled "Concept from 1960s" adds nothing useful to the debate. Before the Wright Brothers first successful flight there had been decades of failed attempts and legions of skeptics saying it wouldnever be done. So? The debate should focus on the viability of a quality design such as Skyweb Express. This kind of debate can only occur when critics take the time to learn about and understand the design. I have yet to meet a PRT critic who has actually read the design documents. No critic of Skyweb Express has to my knowledge challenged the physics, math, or engineering of the design.

The section concerning line capacity reveals a fundamental misunderstanding of PRT. It is a network system, not a line haul system. Unlike in conventional rail transit, passengers are not massed at a few stations to be transported along a few lines. Travel on a PRT network responds to the reality of widely dispersed passengers starting and ending their trips at locations all over a metro area. There is no artificial need for very high line capacity as is the case with conventional transit. Nevertheless, the Skyweb Express system is designed for safe, very short headways and high line capacity. The critics are apparently unaware of the extensive analysis of safe short headway design as produced by Skyweb Express. Initial deployments will not need the line capacity designed into the system. Regulators who impose requirements such as brick wall stopping criteria will have the opportunity to learn about safe short headway operation during early applications of true PRT. As is also the case with emergency evacuation walkways, once regulators understand PRT they will be able to devise regulations appropriate for it rather than mandate preconceived regulations based on old technology.

The section on PRT station congestion really loses touch with the reality of a good PRT design. System simulation by Skyweb Express is not an animation. It operates with the control equations that would drive the actual system components and [to] drive the prototype vehicle. It is incumbent on an honest critic to learn about the control system design and to understand the inputs to the simulation. Only then is a critic ready to challenge the PRT station simulation. The speculations in the article are nonsense. And again, what do the critics fear? If PRT station capacity is truly a fatal flaw as they contend why not let PRT have a chance to fail?

In criticizing PRT cost estimates the article merely states the obvious. A thing can be done well or poorly. If the critics read the Skyweb Express documentation they will learn that every design decision has been rigorously made to minimize the life cycle cost per passenger trip. A vast number of design options could be, and on other systems have been, chosen so as to increase capital and operating costs. Would the critics deny advocates the chance to prove the estimates? If so, why?

Urban citizens all over the world have been concerned about congestion, sprawl, air quality, and energy consumption for decades. During these decades the only alternatives seriously considered have been more road capacity and conventional transit modes. It should come as no surprise that today we are concerned about congestion, sprawl, air quality, and energy consumption. And if our planning studies continue to offer only the same mix of options, decades from now we will still be concerned about congestion, sprawl, air quality, and energy consumption. "Proven technology" such as LRT will not get us where we want and need to go. Transit is almost unique in its attitude against innovation. Automation is bringing substantial benefits to most other industries. Automation could bring enormous benefits to urban transportation. The environmental benefits of widespread deployment of PRT would dwarf those of almost any other technology development. Why is the transit industry so resistant to giving this mode a chance?

In pondering the massive and sustained opposition to PRT, one can ponder motives. Is it fear, fear that PRT might succeed and compete successfully with conventional modes? Is it greed, an unwillingness to allow even a table scrap to go to those willing to innovate? Is it laziness or lack of time that keeps critics from learning the facts about PRT? It is difficult for me to attribute bad motives to transportation professionals. Many of them are friends and peers whom I hold in very high regard. It is a profession characterized by hard work, integrity, and a high sense of public service. However, for reasons that I do not understand, they seem to wear blinders when it comes to helping create advanced tools for their box of solutions.

My suggestion to critics is to adopt an attitude of cooperation. LRT and PRT can be mutually supportive. In my town we are building a massive Interstate highway expansion project that includes LRT. In several cases the LRT station will be at an interchange surrounded by vast office complexes on both sides. If I offered a ride to someone in one of these office buildings and only took them as far as the interchange they would be rightfully disappointed. Transferring LRT passengers to buses would restrict ridership as the buses contended with congestion and riders had to make stops not of their choosing. Would it be unreasonable for planners to simply study the opportunity for PRT to provide the collection/distribution function? LRT would support PRT ridership and PRT would support LRT ridership. It seems like a win-win opportunity to me.

This rebuttal will not change the minds of the critics. Hopefully, however, readers with open minds will learn about true PRT from the numerous sources available and will support giving it a chance to compete with as well as compliment conventional transit. Fear not. The truth will not hurt you.

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