A New Proposed Configuration for the

National Dualmode Guideway System


Francis Reynolds


Agreeing with some dualmode advocates and disagreeing with others, the writer continues to argue that our goal should be a unified national system, since this will solve far more of our many transportation and transportation-related environmental and energy problems. The national dualmode system must be standardized throughout, much as the highways and railroads are. All vehicles on any guideway should be able to travel to any place in the country (nonstop if desired).

The main considerations in my opinion are system capacity, safety, speed, guideway and vehicle life, acceptability to the public, environmental factors, fossil-fuel depletion, total energy consumption, cost of the guideways, and cost of the vehicles. The guideways must carry private cars, transit vehicles, guideway-only transcontinental buses, dualmode taxis, perhaps PRT, light dualmode trucks, and driverless single-mode freight containers.

The local guideways should be medium speed, and those between cities must be high speed. This will reduce highway traffic by a large factor and also reduce domestic airline travel and air freight. In the post-petroleum and post-natural-gas age airplanes may be rare, because there is as yet no adequate alternate energy source for them. We have nuclear submarines, but extensive studies have shown that nuclear airplanes would be next to impossible. And electric airplanes would require long extension cords.

Rental pallets will be needed during the transition period, but little used later.


All guideways must use Linear Synchronous Motor propulsion. This will permit very short but safe headways and thereby achieve a high-capacity system; permit synchronous guideways and asynchronous ramps for simpler control; provide highest efficiency; provide propulsion that is independent of wheel traction in all weather; and eliminate transportation-caused pollution and petroleum consumption. LSM will be the indispensable component in any major optimized high-capacity high-speed dualmode or single-mode guideway system.

Linear induction motors would lack the very valuable advantages of synchronous guideways and would also have lower efficiency. Those who propose the use of rotary motors would not only lose the synchronous guideways features; they would be accepting traction problems and sometimes be literally spinning their wheels. Even with rotary synchronous motors it would be impossible to keep the vehicles synchronized because of minor differences in wheel circumference, and slight slipping between wheels and guideway.


The guideways and the vehicles should be as light and inexpensive as possible within the above constraints, but to eliminate or degrade any of these requirements would be penny-wise and pound-foolish. If we do it right we can build a universal high-capacity guideway system that will satisfy almost all or our ground transportation requirements for relatively little more money than we would have to spend on a single-purpose limited-utility guideway system. We need a major transportation revolution, because nothing less would address enough of our many-faceted problems. Continuing to apply patches to our obsolete transportation systems is not working. Things continue to get worse, not better.

The HiLoMag Team and I have changed our proposed configuration several times in the last few years, as we have thought further, listened to the rest of you, and gotten smarter. These changes might be seen by some as vacillation, but we prefer to see them as willingness to admit our mistakes, and evidence of progress.

The road to wisdom?

Well it's plain

and simple to express:

Err, and err, and err again,

But less and less and less.

Piet Hein

Ways to support vehicles are limited. Pneumatic tires on roads, and hard wheels on steel rails are the most common. Some of us on the HiLoMag Team has lately been reviewing hovercraft and linear-air-bearing technologies for possible guideway use. Floating on air would have some advantages, but the disadvantages also appear formidable.

HiLoMag have previously advocated maglev support of the vehicles on the guideways, but that has been a lukewarm choice at times. In spite of my promaglev October 2000 debate item (which seems to have been partly written to convince myself) I am now going to argue the case for wheels and rails instead of maglev. Since the "Mag" part of "HiLoMag" would no longer fit, for now I will simply use the name "HiLo" to identify this team's changing proposal and ongoing efforts.

I acknowledge that our previous support of maglev has been influenced by the fact that tens or hundreds of millions of dollars have been and are being spent by presumably sane organizations on efforts to build maglev trains in a number of places in the world. I have argued that maglev trains will die in their infancy, because the concept of single-mode coupled trains is obsolete no matter how the cars are supported. But maglev per se would have many advantages in a guideway system. Here are some quotes from an expert in the LSM and Maglev field. This is part of an e-mail Dr. Richard Thornton sent me on Feb. 28, 2001.

"There is more action now [on maglev] than there has been for a long time. We [MagneMotion] may revive our Urban Maglev work. Here is a description of our design objective that may interest you:

"The proposed Urban Maglev design is intended to be a replacement for virtually all guideway-based urban transport systems. This includes commuter rail, light rail, rapid transit, Automated People Movers and dedicated bus-ways. Replacing all such systems is a tall order, but possible due to the inherent advantages of the proposed design. We are confident that an urban maglev system can have the following advantages:

Lower guideway cost than a rail based system;

A high level of automation for demand based scheduling and automated control;

Higher passenger-miles per vehicle per year;

A factor of 2 reduction in average travel times;

Reduced energy consumption, air pollution and noise."

But among the disadvantages of all of the types of maglev are development costs and time, complexity, higher guideway and vehicle costs (in my opinion), and lower efficiency (lower lift-to-drag ratio than steel wheels on steel rails). It is obvious that the question of whether maglev or wheels are the best vehicle support system for dualmode guideways won't be conclusively settled for a long time if ever, but please consider the following nonmaglev configuration.


Several of you have proposed true dualmode cars with pneumatic-tired wheels for the street mode and hard wheels for riding on steel-rail guideways. Some have proposed suspending the cars from overhead guideways and others would support the cars on top of the guideways.

In the supporting-type configuration proposed here, small-diameter rail wheels would be mounted coaxial with and outside of the regular rubber-tired wheels. The regular wheels would be recessed into the car sides a little farther than usual, and the decorative wheel covers would be on the exposed side of the narrow rail wheels. The cars would look automobiles with somewhat thicker wheel covers.

In the event of a power failure on the guideways, the vehicle drivers would again take command and drive off the guideway at the nearest exit by means of the street mode motors driving the rail wheels.

Even though all vehicles on the guideways would have to ride the same rails, the guideways would not be limited to vehicles the size of passenger cars. On larger wider vehicles, such as dualmode buses and trucks, the large "truck" tires required would be mounted not inside but outside of the rail wheels, which will of course again be set to the standard guideway rail gage. That gage will probably be a little wider than the standard railroad gage (which is narrower than that of most automobiles).

In this configuration the rail wheels on the vehicles won't have any flanges. Wheel flanges are required on railroad cars in order to keep them on the tracks, but the modern guidance and switching system to be used on the dualmode guideways will make troublesome, screeching, wear-producing wheel flanges completely unnecessary.

The guidance and switching concept proposed here is essentially unchanged from our earlier proposal, and may be studied in "HiLoMag Supplementary Information" at http://faculty.washington.edu/jbs/itrans/hilo2.htm. It is based on the same concept as that used in the Morgantown Peoplemover and similar automatic systems.

Derailing of cars (in part due to the inherent limitations of the railroad wheel-flange system) won't happen on the guideways. Another factor that will contribute to high safety and rider comfort is the fact that the bank angles (superelevation) incorporated in the tracks will always produce exactly balanced lateral-force-free turns, since the guideway speed will be unvarying.

The rail wheels will be moderately smaller in diameter than the pneumatic tires, so that only the tires will touch the roadbed in street mode. In guideway mode the bottoms of the pneumatic tires will extend below the tops of the rails, on one side or the other of each rail.

This difference between tire diameter and rail-wheel diameter will require openings or breaks in the rails at junctions to allow the tires of exiting cars to pass through the rails. Since the guidance and switching system will be independent of the rails, these rail discontinuities will not present a lateral guidance problem. We will however need to replace the vertical support for the cars at openings in the rails. With this coaxial-wheel configuration that will be easy. We will provide bits of roadway "pads" below the rails in these places, such that the pneumatic tires will ride the pads and support the load until rail support is reestablished.

But since the circumference of the pneumatic tires will be larger than that of the rail wheels, the two types of wheels can't be rigidly attached to each other or there would be forced slipping during switching transitions when the differing wheels share vehicle support. The rail wheels must have separate bearings from the tire wheels so that their relative angular velocities can differ. Planetary gears of the same ratio as the diameter ratio of the wheels will be used between each rail-wheel and the tire-wheel pair to make the tangential velocities of the two wheels equal. That will eliminate all scrubbing wear of the tires at intersections. Elsewhere on the guideways there will never be any tire wear, because other than at junctions the tires will never touch anything.

A simpler system concept, proposed by Kirston Henderson and others, would use the pneumatic-tired wheels on both the streets and the guideways. But I cannot accept the degradation in safety that pneumatic tire use on the guideways would introduce to a high-speed automatic system. Henderson's system provides weather protection for the guideways. When the propulsive power is transmitted through the wheels this is essential in order to guarantee poor-weather traction and braking.

With rails and linear motors weather protection is unnecessary. Wheel traction won't be needed on the guideways in this case since all propulsion and braking will be provided by the linear motors independently of the wheels. Heavy traffic would keep the rails clear of snow or ice in most cases. But where ice does have a chance to build up, derailing will not occur, since the compression strength of ice is only 100 to 1000 pounds per square inch, depending upon conditions. There will be roughly ten times that much wheel pressure on the rails, which will crush and disperse any ice.

However the lower contact pressure of pneumatic tires would not crush ice on the tire support pads at guideway junctions. No wheel traction is needed here either, but an excessive buildup of ice on the pads would cause a bumpy ride at intersections. Thermostatically controlled electric heat for the small pneumatic-tire support pads will therefore be provided at low-traffic guideway intersections.

The high contact pressure between the rails and the rail wheels will also crush and disperse most debris, including tree limbs of some diameter. The guideways will be much less subject to dangers from debris than our existing highways are. For one thing, unlike our highways, which must have continuous solid surfaces, the guideways will have open areas at the side of and between the rails, so that most snow and debris will fall through.

At-grade guideways should actually be elevated several feet to allow debris to fall, and to reduce the danger of the guideways to animals and humans. Additional snow and debris control can be provided by periodically running an automatic snowplow through vulnerable parts of the guideway system. These plows would be designed to sweep the support rails, the guidance and switching rails and, the pneumatic tire support pads at the intersections simultaneously.


REBUTTAL to Problems of Dual Mode Transportation, by Dr. Anderson, 2/19/01

Under "Variable Vehicle Condition," Ed Anderson wrote:

"There must be an organization, private or public, assigned the task of maintaining safety and on-time performance of the automated guideway portion of a DM system. Such an organization must assume that a DM vehicle (DMV) requesting permission to enter the automated guideway may have been off the guideway for any period of time and may be in any condition."

I hate to start out in a negative vein Ed, but I disagree almost completely with this statement. The organization (if any) assigned to maintain transportation safety should instead monitor the much more dangerous streets and highway systems. In many or most states privately owned vehicles are never required to have mechanical safety inspections. Emission tests are required, but they do nothing to assure that the vehicle won't lose a steering link or other vital part and cause an accident.

And the condition of the car isn't nearly as important as the condition of the driver. Drivers, not cars, cause most accidents. We are required to get driver's licenses, but the only test required for license renewal, in this state at least, is for vision. Even if a license renewal is denied that will only get an unsafe driver off the roads at the time of license renewal. Not even then, if the driver chooses to drive without a license.

On the automatic dualmode guideways the human "drivers" will have no opportunity to miscontrol the vehicles. All of the manual controls will be disabled. Only after they leave the guideways will drunk or otherwise unsafe drivers again be empowered to cause accidents.

You mentioned "on time performance," Ed. With LSM synchronous guideways there will never be slow traffic (except possibly in overloaded asynchronous ramps) and never any passing (with its inherent dangers). The system will be completely automatic with only supervisory humans required. Traffic control people are necessary for our airways; but we haven't needed them on the streets since the invention of stoplights. And we won't need them for the guideways, thanks to computers.

"Permission to enter inspections," will be at the point of entry and entirely automatic. Inspection will take only a few seconds, since there will be few components in the cars that could cause guideway accidents by their failure. Far fewer than the number of never-inspected critical parts in an automobile on the highways.

As someone else pointed out in these debates, it is impossible to make any transportation system perfectly safe. The guideways will be accepted if they are at least as safe as the highways, and that goal can be surpassed with few problems or excessive expenditures.

Ed Anderson continued:

"Reduced Station Throughput

The time required for DMV inspection is key to determining station throughput."

Agreed, and since we anticipate the automatic vehicle inspection will take in the order of thirty seconds, we foresee high station throughput.

"Some DM proponents argue, however, that a DM network can have its guideways farther apart than in a PRT network because people will be able to drive to stations rather than walk. But, for a given area coverage and given ridership, the required station capacity is inversely proportional to the number of stations. Thus, a sparser DM network will require more frequent entry and exit points or higher capacity per entry point than a PRT system."

I agree Ed. Fewer guideways will require more station capacity per guideway. To adequately serve a given population will require a certain number of ramps. We can save money, compared to PRT, by reducing the number of guideways, but we cannot reduce the number of ramps. I envision almost continuous strings of acceleration and deceleration ramps paralleling the guideways in densely populated areas. In such places ramp density may dictate dualmode guideway spacing, while the main factor in determining PRT guideway spacing is customer walking distance and/or station-car parking space.

We don't use the word "station" in the HiLo dualmode system, since it seems to imply something large and expensive. We use the word "stops" for the system entry and exit points at the street end of the ramps. These stops will be no larger than parking spaces, and unsheltered.

With regard to your item 5, on combined DMS and PRT, I haven't studied PRT significantly, and am not qualified to comment on possible combinations of dualmode and PRT. We support the incorporation of ample transit service on the dualmode guideways (which can of course be used in single mode as well), but we leave the choice of types of transit to others.

"6. Wide, Expensive Guideway

An advantage of PRT envisioned by many proponents is the possibility of designing a compact, minimally obtrusive guideway . . . Early DM systems were assumed to have auto-like vehicles with one set of wheels that run on either the streets or the guideway. The designers of such systems assumed that the automated guideway would be like an elevated roadway. Unfortunately, such guideways turned out to be too visually intrusive, too expensive, and were not practical under winter conditions.

As a result, DMS designers have proposed either palletized DM, in which small automobiles would be clamped to captive pallets, or that the DMV would have a separate suspension system for operation on the guideway, thus permitting design of a compact guideway. In either of these cases, the DMV or combination of auto and pallet has more parts and is clearly more complex and heavier than a PRT vehicle captive to a guideway, which implies a more expensive guideway because guideway weight increases in direct proportion to vehicle weight. The alternative is the auto-type DMV operating on essentially an elevated roadway, thus accepting the disadvantages of such a guideway."

Your points are well taken. The different companies, teams, and individuals participating in these debates vary widely in what types of vehicles other than passenger cars they would include on the guideways. And we certainly differ in the configurations we propose. I can only speak for myself and to a degree for the informal HiLo Team.

The dualmode vehicle configuration I have described here might add five or ten percent to the weight of a private car. I too would like most of the dualmode cars to be small light ones, but in a free society the size will be largely up to the consumers. However, in the multiuse system we propose, the guideways will of course be designed for a maximum weight and size of vehicle. To pick a number, I suggest that the loaded vehicle weight limit be six tons.

Six tons would be adequate for most delivery trucks and transit vehicles. Present Greyhound TM buses exceed six tons, but we wouldn't need dualmode buses that large. It will make sense to schedule smaller driverless single-mode buses loaded for single destinations. They could then travel nonstop for minimum trip times. These, like dualmode private cars, will be able to reduce airline traffic greatly for short and medium distances. Without the need for drivers the per-passenger cost of operating smaller buses will be closer to that of big buses.

The highways and railroads will continue to carry the big or heavy freight cargoes, but driverless guideway container-like freight vehicles will be extensively used for time-sensitive cargoes that now go by highway or airfreight.

Six-ton-capacity guideways would cost a lot more per mile than one-ton guideways would, but far less than six times as much. The design costs, the land acquisition costs, the permits, legal battles, and many other factors will be largely independent of guideway size and weight. In my opinion it would be a huge mistake to scrimp on the guideway utility or capacity in order to save a few billion dollars. I am thinking of the national guideway system fifty years from now (which we will never have if we don't start building it). We must do this job as right as we know how the first time. A lesson comes to mind from the railroads: Over a century ago lack of vision regarding the future size and weight of locomotives and railroad cars saddled us with a standard railroad gage that is now dangerously narrow.

8. Reduced Line Throughput

If the DMS uses auto-type vehicles, with propulsion and braking through wheels running on a normal roadway, the variability of friction on a wet guideway will result in reduced minimum headway, as compared with the headways possible if propulsion and primary braking are performed through direct electromagnetic action between guideway and vehicle, for example with linear-induction or linear-synchronous motors. The improvement in capacity with linear motors is in the range of two to four and is an important factor in the economics of the system. Thus, in pure DMS, more guideways would be needed than in an optimally designed PRT system, not fewer. In palletized DM, throughput may not be diminished.

Agreed in part, but neither pure DMS nor palletized dualmode are restricted to propulsion through the wheels. A number of dualmode systems have been proposed that would use only LSM on the guideways, including HiLo. Our national dualmode system must use linear motors for traction, and they must be linear synchronous motors to give us the added advantages of synchronous guideways and the higher efficiency of LSM over LIM.

Throughput will not be diminished and no more guideways (maybe less) will be needed for an optimally designed dualmode system than for an optimally designed PRT system.

9. Downtown Congestion Beyond System Control

In a central business district (CBD), DMVs would leave the automated guideway and descend into the street system where the DMS cannot control congestion. Thus, DMVs may be blocked from leaving the guideway and cause vehicles behind to have to be rerouted to other off-ramps, thus increasing flow on what will probably be the busiest part of the network. With the same number of people wishing to enter the CBD as before, a DMS would decrease congestion only if it is designed with PRT-type stations in the CBD and if a significant portion of the people going to the CBD choose to stop and leave their vehicles at the PRT-type stations.

What item 9 ignores is that we will have automatic parking of dualmode vehicles directly from the guideways. Eventually a high percentage of the private DMVs will never leave the guideway system at all in CBDs and other congested areas. This will greatly reduce both street traffic and street parking. The automatic parking could be provided by the guideway system, by commercial parking companies, by businesses in the CBDs, or by all three, just as free or pay parking for automobiles is now provided on streets, in parking lots and garages, and in the basements of buildings. Automatic parking directly from the guideways will not reduce the need for deceleration and acceleration ramps, but it will save commuters and shoppers a lot of time and frustration, and it will greatly reduce CBD street congestion and improve street safety.

In his item 10 Ed Anderson also suggested automatic parking. He wrote:

"An alternative would be to have special DMV-storage facilities under control of the DMS so that the patron would enter such a facility to reclaim his vehicle. The retrieval time would be substantially greater than the wait time for the next available PRT vehicle in a PRT system.

11. Vehicle Usage and Amortization

In a DMS, each vehicle is the private property of an individual, and would be used only by that individual. That is the basic attraction of DM. Thus, the number of vehicles required in a fleet would not be diminished over that in use today. With captive-vehicle PRT, several estimates show that the number of vehicles required to move a given number of people is reduced by a factor between about six and ten, simply because each vehicle is immediately available for another trip as soon as one is finished. PRT vehicles will thus travel several times as many economically productive miles per year as DMVs (not six to ten times because of unavoidable deadheading), which means that, for the same guideway and vehicle costs, the total cost of capital and operation per passenger per unit of distance will be less by the same factor. Consequently, for the same unit cost, DM guideways and vehicles would have to be cheaper than the corresponding elements of a PRT system in the same proportion. Yet, as has been shown DM guideways and vehicles will be more expensive than in PRT. If a DMS has no PRT-type stations, its economics is improved, but with the disadvantage that it is less available to people who cannot drive automobiles.

All very true, Ed, but you ignore the fact that in the United States and most other developed countries the great majority of people (including me) demand the right to have and use their own vehicles. No amount of logical argument as to how things should be is going to change that. And most governments can't and won't change it, because the politicians depend upon our votes. We now pay and will continue to pay more for our transportation than we would need to, because we want the great convenience, pride of ownership, and other advantages of private cars.

When the petroleum is all gone, and/or the streets and highways completely stalled, we could be physically forced to give up our present automobiles. But since the dualmode option has presented itself as an excellent way around these multiple problems, its implementation is inevitable.

12. Elitist Solution

DMVs have all of the components needed to run on streets plus the automatic control system and possibly other components needed to operate on an automated guideway. They will thus, as mentioned, be more expensive than PRT vehicles, and will be available only to the wealthier segment of the population. Moreover, how much guideway must there be before even wealthy persons decide to purchase a DMV? At first, a few of such persons may as a novelty purchase a DMV, but hardly enough to support the construction of the guideway. For political reasons, it would seem necessary for a government to subsidize the purchase of DMVs, so that they would be available to all who want them. For many years, many people would regard the DMS as an irrelevant novelty until there is enough guideway to serve a significant portion of their trips. Yet, in a democratic society, these people would be required to bear the tax burden required to build the guideways. DMS proponents need to describe in detail in a practical, understandable, and acceptable way how the system could expand into a viable alternative transportation mode.

I have to agree with much of what you write here, Ed. Getting a national dualmode system will indeed be a major challenge. And as many of us have observed, the greatest problems will be political, sociological and economic, not technological. I have no pat answers, but let me express a few opinions.

Owning an automobile at all was elitist from 1900 to the 1930s. And we can compare that period to the question of dualmode in another way. There weren't any highways when the first automobiles appeared. The rutted muddy dirt roads that horse and buggy could traverse were far from adequate for automobiles. The elitist and adventuresome early auto owners gradually increased in number, and demanded good roads. Better roads increased the demand for cars, making mass production and much cheaper cars possible. Chicken and egg have to develop simultaneously. The transition period will be painful, but as happened in the early 1900s the enthusiasm for and the huge market for the wonderful new transportation system will assure its success.

The consensus at the end of the National Dualmode Transportation Conference (1974), in which Dr. Anderson participated, was that dualmode was a good idea and should be developed. The reasons why nothing much happened in the field after that favorable assessment are doubtless many, but I think one of the biggest reasons for inaction was that our problems weren't critical enough at that time.

At present we have three types of crises that are putting pressure on us as a society to do something about transportation other than what we have been doing. These three pressures are of course traffic, fuel depletion, and environmental problems. If we had started on a national dualmode system in the 1970s we would be far better off today in all three of these broad areas. The crises are much worse now, but still not quite to the panic stage. Most of these problems appear to be escalating exponentially, so we may be able to get the national attention we need before too long. Maybe we have to grow still worse before we can start getting better. Panic-mode management.

You speak of the "tax burden to build the guideways," Ed. I am against financing them that way. New taxes are always unpopular, and in this case they would be strongly opposed by those who cannot be made to share our vision. Let those who want the system finance it; and let those who use the dualmode system pay off the investment through guideway-use fees. It seems to me, that after the public has had an opportunity to hear about and understand the advantages of dualmode transportation, that "Guideway Bonds" will sell well, just as War Bonds sold during WW 2. The reasons will be similar: patriotism, concern for the world and our grandchildren, and a good investment. The market will be almost all people who travel, not just the two or three percent who can be induced to use transit of some type.

13. The Ability to Drive

Unless one is a passenger, relying always on someone else, DM requires a driver's license. There are many people who are too young, too old, or otherwise handicapped, who either cannot or should not be driving an automobile, and the number of people of retirement age is the fastest-growing cohort in society. PRT is available to everyone. Each individual, regardless of handicap, has equal availability to the system without the sometimes humiliating need to rely on someone else.

Your arguments here apply equally to the status quo. Most people drive; but some people can't, don't want to, or can't afford to. For these people we do and should provide transit in one or more forms. I agree that PRT would have advantages over mass transit for some people, but we cannot view PRT as a substitute for private cars (as you also state). Most people love the freedoms made possible by personal cars, and will never give them up. Dualmode will solve or alleviate our major traffic, fuel, and environmental problems; thereby letting us continue to have private vehicles and letting new members of the expanding population get theirs. Yet a wisely designed guideway system will also serve transit (including PRT), freight, and other commercial traffic.

15. Conclusion

Dual Mode transportation is an appealing concept, but on close examination has a series of fundamental problems that do not seem amenable to technical solution.

Tilt. My close examination has apparently led in different directions than yours. I find no fundamental problems in dualmode that do not seem amenable to technical solution. But I am not opposed to the addition of PRT to the dualmode guideways, if there is a market for it. There will be plenty of capacity to accommodate PRT along with everything else. In the HiLo proposal one guideway lane in the cities would be equivalent to twelve highway lanes, and one guideway lane between cities would be equivalent to forty highway lanes. Welcome aboard.

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Last modified: May 02, 2004