Some Thoughts on Guided Personal Transit 


William G. Turnbull

It would appear, at least to those contributing to the Dualmode Debate page, that there is a general consensus that some form of guided personal transit should, perhaps must, be developed. Beyond this, opinions diverge. I found agreement, more often than not, with Dr. Hopkins observations on political consensus and general requirements for technical advancement.

As a newcomer to this debate, I would like to share some initial impressions. I may well succeed only in displaying my naivete and ignorance, but perhaps some measure of what I am about to say is pertinent. I have listed some general topics that appear to me to require further discussion. As I say, these are general impressions, each may apply more in some concepts and less in others.

Let's consider each of these in some detail. No doubt, some if not all of these impressions and/or opinions will be controversial. Fine! As long as it sticks to the issues, and does not descend into ad hominem attacks, a vigorous debate is the surest way to develop an optimum system.

The scope of some of these schemes is too broad. Specifically, that basically the same system can provide relief for urban problems as well as provide the means for inter-city transit.

I have listed the question of scope as the first problem, not because I think it is necessarily the most important, but because I wish to devote the bulk of this discussion to the solution of urban problems.

I believe the problems of inter-city and urban transit are fundamentally different. For mid-range and beyond (i.e., 400 miles), it is my opinion that to be a serious competitor to airplanes, inter-city transit requires speed approaching something like 300 miles per hour. This places restrictions on the kinds of hardware than can be considered that have no relevance to urban transit. I see no need for urban transit to exceed 100 miles per hour, and in all likelihood less. For example, whether one adopts it or not is another question, standard rail tracks are adequate for the latter. They are probably not for the former.

In inter-city travel there is a question on the relative importance of convenience or comfort and amenities. With dual-mode, the convenience of having your private vehicle immediately accessible is of paramount consideration in many instances of urban transit. For journeys that may last for one to three hours (or more), instant access may seem less critical. The freedom to move about and the convenience of toilet facilities, dining and club cars, and in longer journeys sleeping facilities, will have more appeal. Moreover, the concept of "station cars" is already well developed - they are known as Hertz, Avis et al.

Some have suggested that 300 MPH is too high; that ground travel can become competitive at 150 to 200 MPH. That may be, but it simply enhances the validity of the comfort argument.

As Dr. Hopkins points out dealing with the body politic is not without its difficulty. I concur with his view that creating a national consensus will be particularly difficult. With some notable exceptions, most politicians are timid. They prefer incremental solutions. The prospect of a massive national program scares the hell out of them. As does Mr. Velona, I believe that the prospect of early corporate support is remote. Whether we like it not, we are going to have to get support from the government, at some level. Consideration of what this all means to a politician is critical to developing the necessary political will

Thus, while the saturation of inter-city transportation is, no doubt, approaching - the problem of the breakdown of urban freeways is here, and now. I believe that these programs need not, nor should not, be tightly coupled. The interface between them must be well coordinated, but the problems are different.

An emphasis on advancing a specific hardware concept before a comprehensive evaluation of the problem from a system viewpoint.

Any system of personal urban transit is a massive undertaking. First consideration must be given to operation and control. The requirements of safety are paramount. The fiasco of the Denver airport baggage system should be carefully considered. Remember they were tearing up baggage, not people. Can you imagine the impact if people had been involved?

The question of operation and control is, to first order, independent of the vehicle design, the details of switching, whether it is suspended or supported, and whether wheels or a magnetic field are the means to guide. As discussed more fully later, whether it is PRT or dualmode is also not terribly important. Admittedly, in so called true-dual mode the problems are somewhat lessened; but only in quantity, not substance. The number of vehicles in a non-paletted system is reduced (by just how much needs a careful analysis of traffic patterns), but the basic philosophy of control need, in no fundamental way, be different.

It is true that use of a linear synchronous motors (LSM) may have some effect on the specific means of vehicle control. But this can not be pre-judged going in. First one must decide on the basic mode of operation. The issue of an absolute constant velocity or whether some variation is required must be resolved. The question of whether close contact packets or a continuous line of short headway vehicles, and what that headway should be, has an impact on the type of control. A corollary to this is how to insert vehicles onto the main guideway, and how to insure that a vacancy actually exists. And precisely where it is.

One needs to decide at what level control is effected. Does some massive computer control all, or is control distributed to a number of regional computers, or diffused more generally? To what degree is the vehicle allowed to control its destiny? Is the vehicle provided with independent sensors to monitor abnormal conditions, and is the vehicle allowed to take independent action. How is the decision to branch determined; is this under the control of the vehicle or is it affected by external actions? If the latter, what is the minimum headway that can be considered?

One must consider the implications of data transfer rate and the number of calculations that must be performed with each of these choices. This, in the final analysis, may be the determinant. What is the impact on the overall system if one section fails.

I could go on and on, but I think the point is made, there is a lot to be considered. Many, if not all, can be determined without serious reference to specific hardware. That is not to say that changes will not be required when it is appropriate to consider specific hardware. They most emphatically will; this is unquestionably an iterative process. If, however, one has a total system concept in mind when considering these, it is my opinion, and my experience, that there is a significantly greater chance of making the correct decision if it is viewed in that context.

Perhaps many, if not most, of these choices have already been considered by the proponents of the various approaches. There are indications of this in some discussions. Notwithstanding, I believe that a vigorous discussion of this topic is rather more important than particular hardware issues.

If anything even remotely approaching the Denver airport baggage system problems were to occur again, the consequences for guided personal transit would be enormous. I have no personal knowledge, but I have no reason to believe that the people of BAE Automated Systems were technical oafs. More likely they were competent professionals. Yet they created a technical disaster. The most likely reason is that there was insufficient time and thought given to operation and control. We must not make such mistakes.

Moreover, it is only after these decisions are made, and a comprehensive computer model of the operation is developed, that one can make credible estimates of system capacity. In addition, it is only then, by referencing actual traffic patterns, that one can make an informed decision on whether the use of pallets is a serious problem for dualmode operation.

A tendency to assume that "one size fits all" rather than considering that various localities may require different solutions.

In reviewing the various concepts, I am left with the impression that most of the arguments tend toward absolute and universal conclusions.  An example is the assertion that a particular type of guideway construction is required to protect it from adverse weather. What may be entirely appropriate for the midwest may have no real relevance in the sun belt. Then there is the argument about whether PRT or dualmode is preferable. I think that a compelling case for dualmode is made by the urban sprawl of southern California. On the other hand, the authorities in New York may not be quite so enthusiastic about additional tens of thousands of automobiles descending on Manhattan. Just as the needs of inter-city transit need to be separated from urban requirements, individual localities will likely require individual solutions. Also, as implementation will likely occur over several decades, we must provide for later systems to benefit from earlier experience

There is a legitimate question of standard use. When considering a dualmode system(s), no one would suggest that a separate vehicle should be required for each system in the nation. However, I think that this is more an argument for a pallet, than a standard national system. I will have more to say on this issue later. The point to be made is that one size may not fit all.

A perception that the hardware is "over designed"

Again, I am new to all this, but it appears to me that the various proposals may be overly complicated. Clearly if we are to generate the political will to fund any of these in a serious way (I am talking about the United States, not Europe), we are going to have to convince our political masters that we have a cost effective solution. Thus, at least at this juncture, I wonder if talk about magnetic levitation, overhead suspension and the like is not counter-productive.

It appears to me that it might be useful to develop a sort of minimalist system, if for no other reason than to serve as common point of departure. As an example, would not a more or less conventional rail-based system (similar, but not necessarily identical to standard railroads) be adequate for urban needs. Surely flanged wheels on steel tracks laid on the surface would be less costly than almost anything else. As suggested by some, it might require some traction augmentation. And of course, it must be a limited access system, thus requiring over/underpasses and the like. But basically a surface rail infrastructure.

It may be that a careful analysis will determine that this is not an optimum, but if funding for more complicated, and costlier, systems is to be found, the reasons must be thoroughly validated.

If one had an engineering description of a workable minimalist approach, along with some reasonable cost data, these can usefully serve as the basis for a cost/benefit analysis of the various alternatives. Reynolds believes that a "Cadillac of a system . . . will turn out to be the least expensive, least wasteful, most used system." That may be, but please remember that engineering is a business of numbers. Just because a shiny new technology exists; that, in and of itself, is not a reason to use it. It must serve a cost effective purpose.

The idea that personal transit is a total replacement for freeways, rather than an augmentation of them.

This is just my general impression, it may not be totally correct. However, I do not see much positive emphasis on the concept of guided transit being an extension, an adjunct if you will, of the freeway system. Billions have been spent on these and they continue to serve a useful purpose. No matter how much we might wish them to, they are not going away in the foreseeable future. But in many parts of the nation, they are not just saturated, but over-saturated. A way must be found to extend their capacity, preserve their flexibility and convenience, be kind to the environment, and preserve Hopkins backward compatibility; but not by simply paving over more urban real estate.

This, I believe, is where the best case for guided personal transit can be made. If we are to generate the political will for this, we must provide a plan showing how to build on the existing infrastructure to provide the requisite additional capacity. It would also be quite useful if we could show that due to a significantly greater capacity, guided personal transit might be more economical that an extension of present practice. I think it likely that a case for this can be made.

In this connection, a major portion of the cost would be acquisition of rights-of-way. Thus, I would anticipate that, at least initially, the guideway would be closely associated with a freeway. In many instances, a median exists that can be used. Even if were deemed necessary to encroach on the freeway itself (for instance HOV lanes), the added capability of the guideway would more than compensate the lost capacity of the lane, and thus provide greatly increased capacity for the combined system. Some estimates of capacity suggest that one guideway can accommodate the maximum one-way traffic on the busiest Los Angeles freeway.

Moreover, an adjacent freeway can provide access to the guideway for maintenance, or for resolving a mishap.

As Larry Stern argues we must "Provide an upgrade/growth path for the long term advanced system." For the foreseeable future, the system will include freeways.

That some of the arguments between modes of personal transit are more apparent than real e.g., personal rapid transit and dual-mode.

Aside from the obvious i.e., the actual vehicle itself; if we consider a paletted dual-mode system and a PRT system, from an operational view, they are essentially identical. If we were to consider each as an individual system, there is no reason to believe that we would choose a different guideway for each or that we would choose a different means of propulsion, or a different control system. They both also suffer from the need to return "empties" to wherever the demand is.

As I suggested earlier, the specific needs of New York and southern California are different. I am also sure, that even within a community, there are different needs. If your destination is the central city, it is increasingly likely than not that it is not useful to bring your private automobile.  From suburb-to- suburb, it may be essential. But from a system standpoint, the choice does not have to be made. The distinction between them is more the impact on the surrounding area, rather than the system itself.

We can easily restrict dualmode access to certain destinations, and perhaps certain times, and have both systems operate smoothly together.

Which brings us to the question of to pallet or not to pallet. A great deal has been written on the pro's and con's of this question, and I am not going to repeat it here. Judging by recent posting to the Dualmode Debate page, the pendulum is swinging toward palleting. I have to agree, if for no other reason than I think the "chicken and egg" question remains insoluble. Thus if we require pallets, at least initially, we must design a paletted system. If some time later, we become sufficiently wise so as to eliminate the need for a pallet, it poses no additional burden on the system - quite the contrary. So if we do not have to make a decision between dualmode and PRT, and the question of a pallet is resolved, why are we still talking about them.

One reason may be that there are good arguments to consider pallets that do not impact directly on a specific design. I believe Dr. Hopkins is quite right when he suggests that we should not integrate the private automobile too tightly to the infrastructure, and that there is a need to preserve backward compatibility. By requiring a standard only on the means to talk to the system, and for the connector to provide housekeeping power, we satisfy both of Hopkin's requirements. With only these two standards, one can operate anywhere in the nation, without the need for a national system.

Any system of the kind we are considering will take decades to implement. Moreover, different communities will begin at different times. We can be sure that any design originating 20 years from now will be quite different than anything presently being considered. Unless, that is, we adopt some stultifying "standard system" that precludes this. As Hopkins states, adaptability must be preserved.


Last modified: May 27, 2001