Some thoughts on an


William G. Turnbull

With a view to somewhat wider distribution than these pages, I have drafted a report that attempts to outline the numerous advantages of an alternative to continued reliance on freeways for urban transit. While the report relies heavily on dualmode concepts, I suggest only a general approach to a solution. The purpose is to generate broad-based support for change, rather than solicit allegiance to a particular scheme. That there is a problem in urban transit is well known to readers of these pages.

While today the freeway system plays a predominant role in urban transportation, most would agree that the policy of continued expansion of these vital arteries is rapidly approaching the end of its usefulness. Nonetheless, we can not afford the luxury of scrapping an extant system and starting over again, anew. Any solution must build upon what we have. Moreover to be successful, it is essential that any proposal must facilitate and provide a road map for how we get from here, to where we need to be.

The most commonly expressed "solutions" such as light rail and its more exotic cousin, monorail, have been singularly unsuccessful. They succeed, for the most part, only in transferring people out of busses; they do not reduce freeway traffic

The reason for this failure is straightforward and obvious - people are unwilling to forgo the flexibility and convenience of their private vehicle. Thus any solution, to be successful, must accommodate the strongly held belief that flexibility and convenience are, somehow, inalienable rights.

Two approaches satisfy these "rights", and also appear to be viable candidates for both a practical and economic solution. These are dualmode (DM) and personal rapid transit (PRT). They are listed separately only because many treat them as distinct, as does much of the literature. I firmly believe they are not. I believe them to be two variants of the same thing. In a very real way, one can be considered an extension of the other (i.e., a DM system can be a precursor for PRT, or both can operate simultaneously on a single system).

As readers of these pages well know, both operate automatically, without the need of an operator, on a guiding structure or guideway. They can operate simultaneously on the same infrastructure without loss of benefit to either. The principal reason for choosing one over the other involves the population density at the origin and/or destination locales. For instance, the introduction of additional vehicles into Manhattan in New York City could hardly be considered a positive benefit; whereas a street vehicle would be considered essential to completing the journey in sprawling southern California. Accordingly, I have chosen to eschew either term, and entitle the discussion an inclusive Individual Rapid Transit

I make no claim as the innovator, or original proponent, of any great amount of the material presented. Although, perhaps, some progress in terms of control philosophy is provided. In this connection, this philosophy is applied to a model of the actual traffic on a real freeway (the San Diego Freeway). While considerable more work is still to be done, I believe that it represents an encouraging beginning. Peak traffic of something like 15,000 vehicles per hour is indicated.

To the degree practical, I have attempted to avoid discussion of specific hardware and limit the discussion to requirements as viewed from a system standpoint. However, in order to make clear what is required, some consideration of hardware is inevitable. What I hope to accomplish is to provide an overall operating philosophy. It is not by accident that special emphasis is given to control. I believe that for most people; this is the paramount concern; not the details of guideway, or vehicle construction.

Thus the real purpose is to lay out to a broad audience of elected officials, policy makers, influential private citizens, and the general public the many advantages of a transit approach along these general lines. Thus to many here, much of what is said is old hat.

While no particular design advocated, I am not without prejudice. This shows up perhaps most clearly in the rather insistent stance on the necessity of the palletted variant of dualmode (i.e., the car-ferry approach). At least for initial installations, I feel the arguments for this are compelling. However, I do understand that this is not a universally shared opinion.

In a similar vein is the question of elevated guideways. Certainly guideway traffic must be isolated from other traffic or obstructions, and that in furtherance of this many over/underpasses and other means of separation will be required. Moreover in some instances, circumstances will dictate that extended distances must be elevated. However, this is quite different from requiring, at the outset, that all guideways must be elevated, no matter. I believe that, particularly along or adjacent to existing freeways, this isolation can be effected at grade. Although this view could have significant economic consequence, this opinion is practically unique.

Another somewhat contentious issue, is the view that these systems should be stand-alone, separate from private automobiles and freeways. Indeed, some hold that private automobiles should be done away with altogether. I disagree; I am of the view that these systems must be properly integrated into the whole of the transportation infrastructure. These should be considered as an augmentation of, not a replacement for, freeways - a continuing evolution of our transportation system.

Moreover, in considering cost; I suggest that these should be considered in relation to the cost of freeway, or other construction, to meet the same need - not as some additional burden on the taxpayers. This is of particular importance when the alternative is double-decking an existing freeway. Indeed, it may be possible to finance this with some sort of revenue bonds, obviating additional taxes altogether.

There are undoubtedly numerous other areas of disagreement.

It is not essential that all, or even any, agree with every detail presented. It is only important that some appreciation of the many advantages of this general approach is achieved. Again, the purpose is to provide to a general audience a sense that consideration of these can lead to a practical and economic solution to the problems of urban transit. Sadly, we are led to believe that simple technical merit is insufficient. It is necessary, but not sufficient. Only by generating a public clamor, will substantive change come about.

Finally, in keeping with our objective, and to facilitate review by a technically diverse audience, the report is divided into two parts. For those wishing only a cursory discussion sufficient to appreciate the many advantages of this approach, it is only necessary to review Part One (Sections I through III). Those wishing more detail will find this in Part Two.

The report, in its entirety, may be found at the link indicated below. I invite and welcome constructive criticism.

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Last modified: August 05, 2002