Personal Rapid Transit versus Dualmode Transportation
by Francis D. Reynolds
Comparison Table - PRT and Dualmode Transportation Systems
Factor PRT Dualmode Technologies needed Available Available Power Electric Electric in both modes (eventually System Cost Very high Fewer lines and stations required Will it carry PRT cars? Yes Yes Carry private cars? No Yes Carry transit buses? No Yes Carry freight? No Yes Carry light trucks No Yes Resultant market Low Enormous Financial subsidies Probably needed Not needed Reduce air travel No Yes Provide door-to-door service No Yes Resultant popularity Low Very high Transportation safety Some improvement Great improvement Rights-of-way required Many Fewer Environmental impact Slightly favorable Very favorable Energy impact Sightly favorable Very favorable Note: Not all proposed dualmode systems would satisfy the above. A maglev LSM system is assumed
This chart shows the writer's views on dualmode transportation compared to Personal Rapid Transit (PRT). In the chart the advantages of dualmode are overwhelmingly greater than the advantages of PRT. Therefore, at first glance, it would seem that no intelligent person could possibly favor PRTbut some intelligent people do.
With deeper study I can see several reasons why certain people would favor it. Some of these people are trying to start a PRT business, and are looking for niches in which they might make a profit. Dualmode is a more complex and revolutionary undertaking; therefore it will take a lot more effort and it is less apt to generate near-term profitable niches. However I am aware of several startup companies that initially proposed PRT only and later added dualmode to their systems when the great advantages of dualmode became evident to them.
Another possible reason for preferring personal rapid transit is that "transit," is an old word that people understand. Various transit systems have served the world well for a century and a half, but now transit of all kinds carries only two or three percent of the travelling public. Even a "personal" transit system would be unable to reduce more than a few of our major transportation and transportation-related environmental and energy problems.
Most transportation planners continue to think only in terms of systems they already know. They also know, but may choose to ignore the fact, that nearly all transit systems that once made profits are now heavily subsidizedautomobile travel is clearly the mode of choice. But the planners still desperately try to solve the serious problems caused by today's huge number of cars by proposing the only alternatives to automobiles they know ofmore transit of basically conventional types.
But why alternatives to cars? Cars provide the best transportation man or woman ever invented. Therefore, rather than try to suppress these wonderful machines we should keep them but change them and their uses in ways to eliminate their shortcomings and further add to their usefulness and capability. The automobile companies are doing some of that, however so far they are missing the most important major step of all: dualmode. But that will change. Five years ago I wrote to Daimler-Chrysler, Ford, and General Motors on the subject of dualmode, and didn't get a knowledgeable response from any of them. But more recently both Ford and GM have contacted me on dualmode.
Those who have conceived of and designed PRT are more observant and more creative than are the planners who stick with the past. PRT proponents recognize that two of the advantages that led to the popularity of private cars are flexibility and privacy, so they propose a transit system that would provide privacy and more flexibility, and they toss in some environmental advantages as well. But why do the PRT proponents stop there?
Building a guideway systemany guideway systemwill be the hard part, the expensive part, and the controversial part. But if we build the right guideway system it can carry dualmode private and commercial cars as well as PRT, buses, and freight. And it will pay for itself as well as reduce the traffic on our streets and highways many times better than PRT alone ever could. Amazingly that dualmode guideway system will cost less than an adequate PRT system would, because dualmode will require far fewer stations and guideways. PRT customers won't be willing to walk very far to a PRT stop, especially in foul weather. With dualmode the travelers can drive their own cars in street mode, for several miles in some cases, to the nearest guideway entry. Occupants need never leave those cozy dry cars through initial manually driven street mode, travel on the automatic guideways, and street mode again to drive to their final destination.
Since the dualmode guideways will carry many different kinds of traffic they will help solve problems in a number of areas other than commuting; but the most important advantages of dualmode over PRT will be the services it will provide to users of the almost universal personal car. Dualmode will let us keep all of the advantages of cars and in addition it will reduce travelling time and stress while increasing safety. PRT would rob us of the highly desirable door-to-door service we now have, and would increase rather than decrease our traveling time. Outside of a dictatorship no amount of pressure to use some form of transit is going to make most people stop driving their cars.
For these reasons dualmode will be many times more popular than PRT. But if there is also a market for PRT, these small automatic rental cars can be added to the vehicle mix on the dualmode guideways.
With maglev and linear synchronous motors, in most areas a single guideway lane in each direction will have capacity enough to accommodate the entire combined traffic load. In and around towns and cities, a 60-mph (100-kph) synchronous guideway will have approximately the capacity of twelve highway lanes, and one 200-mph (325-kph) intercity guideway will have the capacity of forty highway lanes. These remarkable numbers come from the unvarying full-speed operation of the guideways, and the extremely close spacing of the cars made safely practicable by their synchronous propulsion.
No intelligent comparison between PRT and dualmode can be made without defining the kind of PRT we are comparing to what kind of dualmode system. Many different configurations have been proposed for each. An example of this apples-and-oranges problem is seen in a paper titled "Problems of Dualmode Transportation," written 8/15/96, by J. Edward Anderson. In it Doctor Anderson defended his version of PRT and presented a number of "problems" with dualmode. But the early dualmode model upon which he based his conclusions was quite different and much poorer than the maglev synchronous guideway configuration upon which this present paper is based. Most of Anderson's criticisms of "dualmode" do not apply here.
In addition to maglev and synchronous propulsion, the guideways of my dualmode model for these comparisons with PRT are of moderate-size and capable of carrying light freight loads and midsize existing automobiles on pallets. The final guideway sizing will be a political and social as well as a technical decision however. Hopefully we, as a nation and civilized world, will soon come to our senses and start sizing out private transportation to fit our needs rather than our egos. The imminent petroleum depletion and resulting meteoric rise in fuel prices will do wonders to speed this necessary change in consumer thinking.
All dualmode guideways will be electric powered. We might still have some internal-combustion-powered cars when the first dualmode guideways become available, but the street-mode power for the bulk of the dualmode cars will soon become clean green batteries, fuel cells, or some as-yet-undeveloped source. Please note that the limited power and range that make batteries and fuel cells inadequate for use in present automobiles will be quite adequate for the limited-mileage low-urban-speed requirements of the dualmode-car's street mode.
As has been observed in a number of articles on dualmode, the early guideways will doubtless carry single-mode cars on pallets. Later true-dualmode vehicles will become available, eliminating most of the need for pallets. However, it is doubtful that present-day IC cars will ever be put on individual pallets on dualmode guideways, because our present cars will be worn out and replaced by something different before the dualmode guideways become available.
In the meantime the use of multiple-car pallets or car ferries to carry automobiles on existing highway lanes or railroads is very promising. This type of early dualmode is already in use in a few places, and it is working. One such service, using AMTRAK rails along the East Coast of the USA, is reported to be the only part of the entire AMTRAK system that is making a profit.
I also favor the Evacuated Tube Transportation (ETT) concept for longer trips. ETT will eliminate weather problems; and greatly reduce the aerodynamic drag losses, thereby allowing much higher speeds with reasonable power. ETT can also be dualmode, with tubes of moderate diameter. The evacuated tubes, like plain guideways, can be on the surface, elevated, or tunneled. Relatively low-cost surface tubes, with windows to prevent claustrophobia, may make a lot of sense across the prairies. Perhaps ETT will be chosen for the high-speed intercity dualmode guideways at the outset. This would all but eliminate domestic airline travel and its many disadvantages. (Don't tell Boeing, my second home for forty years, that I wrote this.) If ETT doesn't ground the jets, the lack of petroleum will. But evacuated tubes, like open dualmode guideways, are at least two decades away.
At this point we shouldn't dwell upon the cost. We hate high taxes, but the dualmode guideway system will not be built by taxation. Sure, cost is an important factor; the system must be designed wisely. However, building a cheap but inadequate guideway system would be the worst thing we could do at the beginning of this dualmode revolution. The traffic loads on the merchant marine system, the railroad system, the highway system, and the airline system all started out at zero and gradually increased; but the traffic wanting to use the dualmode guideways will be enormous at the outset. Here we must think big and wisely from the start, because we couldn't afford the cost or stand the traffic jams associated with tearing up an inadequate dualmode guideway system and rebuilding it a few years after it was first completed. "Penny wise and pound foolish" is an old maxim, but it fits the initiation of dualmode transportation perfectly.
I am sure that I will receive a number of rebuttals to the comparison chart at the beginning of this article. And some of the counter arguments will be sound. But we shouldn't sweat the little stuff. Charles Kettering, inventor of the electric starter for automobiles and former General Motors Vice President, wrote something to the effect that many people will dwell upon the one percent of a new idea that may be a problem, and ignore the ninety-nine percent that is good about it. Little problems can be solved laterI prefer to look at the big picture at this point. We must have a transportation revolution, not more of systems that have seen their day. Trying to resurrect something that is dead is never successful unless we can first remove the cause of death. Removing our personal cars is neither possible nor desirable.
To those of you who still prefer PRT and reject dualmode, please show us a chart the reverse of the one at the head of this article. Show us, if you can, the areas where PRT would be a better solution to the world's transportation, environmental, and energy problems than a standardized dualmode system will be. PRT would be one small step; dualmode will be a giant step for mankind (at less cost than the small step). Winston Churchill wrote, "One cannot leap a chasm in two jumps." With only different types of patches on our existing transportation systems (and I classify PRT as just another patch) we would still be on the wrong side of a huge chasm. And that chasm would still contain great traffic, pollution, and energy problems. Forget PRT, it wouldn't begin to do the job that has to be done. Dualmode is the only type of system that anyone has thought of that could really span this wide and complex sociological and technological transportation chasm in one jump. But getting such a system built will be one of the greatest challenge civilized man has ever faced.
It will be done. I have faith in the eventual wisdom of my fellow man and woman, but I also have a lot of concern in that area. My real concern is the time that this project will take, and our delay in starting it. Caution is certainly needed, but all of the time and money being wasted on projects that could accomplish little is not only maddening, it is destroying the traveling public's faith in our ability to do anything intelligent and cost-effective in the broad area of transportation. The majority of the continuing planning failures stem from the fact that none of our traditional transportation systems used independently can solve our problems anymore. Dualmode, the new kid on the block, will, but it isn't adequately known or understood in the right places yet. We needed a dualmode system several decades ago. It will be at least several decades more before we can possibly get it designed, approved, developed, and built. The magnitude of our traffic, environmental, and energy problems will far surpass "enormous" by then. I won't have to suffer through these coming major crises personally, but my children may and my grandchildren will.
I hope this article will produce another dualmode convert or two. Welcome aboard. We can use all of the support we can get. Introducing a major innovation is always very difficult. Only a few from the general population have the vision and courage to jump on board immediately. That was true with all of our present transportation systems when they were innovations; and it will be doubly true of our coming National and Worldwide Dualmode Transportation System, because things are nowhere nearly as simple as they were a century or two ago.
Those who wish to know more about dualmode transportation are referred to the DUALMODE and the DUALMODE DEBATE pages at this website.
Last modified: May 03, 2004