Platooning, Car Coupling, and LSM


Francis D. Reynolds


Welcome to Jerry's Dualmode Debating group, Jim. Your broad experience with Boeing, NAHSC, ITS, FORD, GM, et al is most welcome. You and I might have met at Boeing, on Dynasoar. Later I got to manage part of the Boeing Morgantown-People-Mover program, a "down-to-earth" project. I submitted a patent disclosure on a dualmode system to my boss on that program, and got about as far as you did with PAC-ITS. NIH is indeed a powerful and most frustrating force. But congratulations to you for your part in getting NAHSC cancelled. Occasionally common sense prevails.

Your WHSSSH has many good features (the ones it has in common with my HiLoMag thinking, of course). However Jim, I am at odds with you, Charl, and some others on a number of points relating to platooning and car coupling. Also I want to beat the drum for linear synchronous motors (LSM), but first a couple of other items.


Jim Haugen seemed like a "we can-do" person on July 10 when he presented his WHSSSH concept, but on July 14 Jim worried about a lot of problems. Good. If we are to be taken seriously and gain credibility we must be realistic and look at the whole picture. I know from personal experience that it is very easy for an optimist to go hog-wild in this game and paint a totally rosy picture of some system while ignoring all of the difficult problems that would invariably present themselves.

I note that most politicians look upon our work with pessimism—because they know how difficult it is to get something done—even on a local scale, let alone nationally or worldwide. And those in our innovative transportation fraternity who seem to be the most pessimistic about the future tend to be those most experienced in the ways of government. They have been there. Naming two, we have realist John Hopkins and now Jim Haugen.

The heck of it is that the concerns they express are very real and will be extremely difficult to deal with. Yet there is no question in the minds of most of us that a dualmode system is desperately needed and could solve or reduce a high percentage if our transportation, environmental, and energy problems. I like Bill Turnbull's statement, "I, for one, believe it deserves one hell of a try."


In my opinion we must build a guideway system that will be able to rapidly and efficiently move private, commercial, and transit vehicles to within a few miles of their final destinations, whether that is five miles away or across the nation. Our streets connect to our roads and highways so there are no interruptions. Our guideways must do no less.

Local one-at-a-time efforts with obsolescent systems are not solving the many problems. Traffic congestion, pollution, and petroleum depletion constantly get worse. We desperately need a nationwide and worldwide transportation revolution. Our studies have shown that dualmode is by far the best form for this revolution.

But we do have a choice as to which we build first, the intraurban or the interurban guideways. (I rode interurbans, by that name, in the 1920s when I was a small boy, but with the advent of automobiles the interurbans lost money and disappeared. Now our desperate planners think that interurbans would again solve some of our problems. But people know that "interurbans" are obsolete losers, so to avoid that connotation we now call exactly the same system "light rail.")

I agree with those who think the traffic problems in and around our metropolitan areas are the most serious, and therefore I think that the urban guideway systems will be built first. But they must all be built to the same design and standards so that they can all be interconnected at a later date; like our interstate highway system connects with city streets.

Anything we do anyplace, especially in densely populated areas, is going to upset some people. There will be protests, there may be violence, and there will be lawsuits. These things are occurring all over the world wherever any group tries to add or change a transit system. That is now par for the course. But the installation of a good dualmode guideway system would be little more disruptive than the installation of a new dedicated transit system that would accomplish next to nothing. There is moderate support for the stupid systems; there ought to be far more support for an intelligent system. But admittedly majority support won't come easily.


Haugen discussed the disadvantages of elevateds at some length, but I don’t think he mentioned subways. I have ridden the "Els" in Chicago and New York, but I have ridden far more subways, including those in Berlin. My guess is that there are many more miles of tunnels in the world than there is elevated track. And we already drive cars in mountain, seaside, and under-river tunnels. Perhaps driving in tunnels is stressful for many people, but in dualmode-guideway tunnels we won't be driving, we will be passengers just as we are in subways, airport, railway tunnels, and the channel tunnel. I have no figures, but I would guess that subways cost a lot more to build than elevateds. Nevertheless, many cities worldwide chose to build subways to reduce surface problems without introducing El problems. We can build underground dualmode guideways where necessary for the same reasons.

I have always thought that our dualmode system will be a combination of subway, near surface, and elevated guideways, depending upon local land costs, terrain, traffic, population, building density, and other factors. That is the way we do it with roadways and railroads; dualmode should also use all three options.


I keep seeing statements that imply that the only way to get a dualmode system is to have the government (taxes) pay for it. No. We had to have "free" streets because it would be impossible to collect tolls for their use. Gasoline taxes are fair and make sense to pay for roads and highways. Fares and tickets paid for transit systems and railroads until automobiles took away most of their business and government bailed them out with progressively higher subsidies. Dualmode guideways can be financed by "Guideway Bonds" and easily paid for and supported by automatic billing of all vehicles that use the guideways. Transit systems are now socialized because the market for their services is so poor. Dualmode guideways will be financially successful because they will have an enormous and growing market.


Coupled trains (which are necessary when unpowered railroad cars are pulled by a locomotive) are inflexible and result in a lot of wasted time in marshalling: making up trains, getting cars out of the middle of a trains, recoupling, et al. There is a constantly recurring car-sorting problem. And the whole train has to stop at every station, which costs energy, time, and customer good will. Automobiles and highways have no such problems because the vehicles are self-powered and independent. Each can go exactly where it wants to go, at any time, with no restrictions imposed upon it by other vehicles (except for traffic congestion, which is one of the major problems we will solve with dualmode).

Since coupled trains have the above problems as well as others, a major objective in my formulation of a dualmode system was to get rid of coupled-train problems by keeping the cars uncoupled and independent of each other, as they are on highways. That means, of course, that each car must provide it own propulsion, and the cars must have some system to keep them from colliding with each other.


With ordinary automobiles (and in the street mode of a dualmode system) collisions are hopefully avoided through the skill of human drivers. On the guideways we might use human drivers (heaven forbid); a complex proximity-sensor, computer, velocity-control system ala AHS; or—by far the best—Linear Synchronous Motors. In my mind LSM is the most vital component to include in an optimum dualmode system. LSMs will simplify the system and increase safety on the guideways; and they will allow very close headways (without mechanical coupling) to increase system capacity and reduce energy consumption through drag reduction.

LSMs are quite well developed, are highly efficient, and highly reliable. They are used on most if not all maglev trains, on some modern roller coasters, on new aircraft-carrier jet-fighter catapults, in materials-handling systems, in robotic assembly, and they are being studied for space-vehicle launchers. The reader is referred to the 2000 textbook, Linear Synchronous Motors, by Gieras and Piech.

There are two basic types of linear electric motor, linear induction motors (LIM) and linear synchronous motors. LIMs are of no interest to me for dualmode guideway use because they lack the very valuable synchronization that LSMs provide, and they are also less efficient. However, both LIMs and LSMs would provide full thrust even under the slickest guideway conditions, and without going to angled monorails which increase wheel traction by increasing tire load at the expense of added rolling friction and added tire and guideway wear. Whether a vehicle is maglev or wheel supported, if it has LSMs it does not use wheel traction for thrust. LIM vs. LSM, and wheels of various kinds vs. maglev, have been subjects of many earlier debates here.

With apologies to those of you who have heard me say most of this before, LSM-powered cars on the guideways will hold constant spacing like boxes on a conveyor belt do. Boxes on a belt are in essence coupled together by the belt, while railroad cars use steel couplers. LSM cars on the guideways will also be coupled together, but by a constant and precise magnetic wave rather than by visible couplers or a belt.

Another way to appreciate the synchronization of cars driven by LSM is to compare them to plug-in AC electric clocks. All such clocks on a given power-grid keep exactly the same time, because they are all synchronized with the same alternating-current frequency. For a better comparison with LSM guideways, let's go down a row of houses and set an AC clock in each house one minute ahead of the clock in the preceding house. Even if there are changes in power frequency or power interruptions each AC clock in that row will continue to be separated or spaced from its two closest neighbor clocks by a reading of "one minute." These clocks are still all synchronized with each other and have held constant spacing.

We can also compare LSM cars with surfing. If there is one surfboard on each of a series of waves no board can ever catch up with the board ahead. Each is synchronized with its own wave; therefore (ignoring lateral travel) they are synchronized with each other. Likewise, each LSM car will ride its own AC magnetic wave.

Even though the velocity of all LSM cars on a guideway will be constant they will sometimes require higher or lower thrust, and sometimes even negative thrust. Braking (negative thrust) will be needed to maintain a constant velocity on steep downgrades or with a tailwind exceeding guideway speed. This "maintain-speed" braking is provided "free" and automatically by the LSMs as required. It takes just as much external torque to make a synchronous motor rise above its synchronous speed as it does to make it drop below its synchronous speed. This overspeed-resisting effect is called regenerative braking. It also saves energy by pumping some in-phase AC power back into the line.

Dualmode cars will have hydraulic brakes for use in street mode, but for safety's sake there must be no brakes (other than the LSM regenerative braking) that can be used while the cars are on the guideways. Individual cars stopping on the guideways would cause pileups the same as they cause pileups on the highways. If there is a guideway power failure all of the cars will coast to a stop while maintaining their spacing through autosynchronization (which again uses regeneration).

Pardon my dwelling on synchronization for so long, but synchronizing the cars on the guideways by LSM is so simple in principle, and so useful, that it must be recognized and studied. If no insurmountable technical problems crop up when the design details are addressed, and I don't think they will, this is by far the best way to build a guideway system. In my opinion trying to save money by building a lower capacity, slower, or less safe system without LSM would be penny-wise but pound-foolish. Further, there is no data that I know of to show which system would be the least expensive; one using proximity sensors and velocity control, or one using LSM.

Using conventional rotary synchronous motors in the cars instead of LSM has been proposed as a money-saver, since miles of LSM stators wouldn't have to be built into the guideways. But rotary motors instead of LSM present three problems: First, trolley wires and car power-pickups would have to be provided. This is a minor problem. Even with LSM we may decide to put the armatures in the vehicles instead of the guideways and therefore need trolley wires anyway. A more serious problem is that we would again be dependent upon wheel traction for propulsion.

The worst of the three problems is that even though we would be using synchronous motors we would not have complete synchronism between the cars on the guideways because of minor differences in wheel circumference from car to car, and minor wheel slippage. Some cars would slowly creep up on others or slowly fall behind, even if they used steel wheels on steel rails. The only way synchronous guideways could be achieved with rotary-synchronous-motor cars would be to use rack-and-pinion drive. That would present major wear problems and be very noisy at high speeds. The only places rack-and-pinion drives are used in transportation are on a few mountain railroads for tourists where the grade is too steep to depend upon wheel traction.


If all vehicles on the guideways are always running synchronously on the applied AC power, then the computer will have an exact record of where every vehicle on each guideway is at every split-second, by dead reckoning. Dead reckoning will be used for both merging and navigation.

Old-time sailing ships usually navigated by instrumented observations of the sun and the stars. But when the weather prevented celestial navigation they had to fall back on dead reckoning. That involved calculating new latitudes and longitudes based upon a starting latitude and longitude, the length of time the ship sailed on each tack, the average speed on each tack, and the direction of each tack. None of these data needed for dead reckoning could be obtained accurately in those days, and "dead" was sometimes the outcome of resulting errors in "reckoning".

Perhaps as a result, the word "reckon" is sometimes used to mean estimate or guess, but dead-reckoning calculations provide perfect answers if they are based upon perfect data. On the dualmode guideways with LSM the computer will know all of the data exactly and therefore know the exact position of each car at all times. Some people have suggested using GPS for navigation on the guideways. Forget it. Dead reckoning will be far more accurate, more reliable, simpler, and cheaper.


There are, of course, two good reasons for close spacing (platooning) of groups of cars on the guideways: high system capacity, and as much as a fifty-percent reduction in aerodynamic drag. I accept the use of the word "platoon" here only if we don't also imply a sense of belonging, common origin, or a common destination for the cars in a platoon. "Queuing" or "convoying" might be better words. Cars in HiLoMag platoons would share temporary proximity, nothing more.

A system where the platoons would be made up offline, and/or exit the guideway at a single destination, would retain some of the disadvantages of our obsolescent railroad trains for no useful purpose. Cars on a highway, or independent cars on a guideway, are far more flexible, provide faster service, and are free of marshalling problems. Any car must be able to enter the guideway system at any entrance ramp regardless of its destination, and without waiting for a platoon to form (Haugen estimated ten minutes for forming his platoons). When it is done right a car will be automatically demerged at the exit number chosen by the customer regardless of the destinations of other cars in the platoon it happened to travel with. An exiting car will no more affect the other cars in a platoon than a string of cars on a highway is affected by an exiting car. The dualmode system I see is far more like our highway system than it is like a railroad system.

With LSM we can achieve platooning automatically without changing the speed of any car on the guideway at any time. And it will be achieved without "pre-platooning" and without mechanically coupling the cars. Guideway platoons will be automatically and gradually formed on the guideways proper at synchronous speed. The computers that do the merging will be programmed to position entering cars the standard clearance-distance from cars already on the guideways. But the computers will be programmed to enter a car separately from a platoon if it is not possible to join it with an existing platoon within a few seconds. That isolated car will be the nucleus for another platoon. If in heavy traffic all of the platoons have combined to form a single solid line of traffic, that guideway is running at full capacity.

The "specified" minimum clearance between HiLoMag LSM cars on the guideways is one foot. That is admittedly a guesstimate, but I feel it is a conservative one, even at 200 mph. By contrast, if memory serves me, NAHSC proposed thirteen-foot minimum clearance at speeds less than half that. The capacity of one 60-mph HiLoMag guideway (around the cities) would be equal to twelve highway lanes, and one 200-mph guideway (between cities) would equal forty highway lanes. One reason NAHSC was disbanded is that AHS offered little more than existing highways do.


Haugen proposed, "Twenty or so vehicles are mechanically linked into unit trains while on the guideway. A piloted vehicle leads each unit train." No thank you, Jim. Automobile drivers, train engineers, airline pilots, and ship captains all cause the majority of the accidents in these various modes of transportation. On dualmode guideways we can and must get human operators out of the loop. They aren't the least necessary here. Computers can do the job much safer, faster and cheaper, especially in an LSM system. The Morgantown People Mover doesn't use drivers, nor do the shuttle trains at SeaTac, Denver, and many other airports. Let's take another step forward with our dualmode system, not a step back.

If it is shown that we must have a human or two in the loop for some reason, please put them in a control center someplace, like railroad and airway controllers are, not on the guideways where they become part of the problem. Human air controllers are necessary because they have to communicate with human pilots in a verbal language. With no drivers on the guideways that type of requirement for human guideway-controllers is absent. Computers can talk with other computers infinitely better than they can with humans. The machine in front of me tolerates my limitations only grudgingly.

We have read that NASA would like to get all humans out of space flights because computers could do it all much better and cheaper, as they did on the Mars landing. There are no humans aboard our communication or GPS satellites. NASA is sending up astronauts not because they are needed in our space research programs, but because it is easier to get appropriations out of congress when there are humans involved.


As to Jim Haugen's "mechanical linking," physical coupling of the cars is unnecessary with LSM. With maglev (which I prefer over guideway wheels of any kind) in addition to LSM, it is hard to imagine any serious car failure mode that would have an MTBF low enough to be of significant concern. But if those who trust visible steel couplings but don't trust magnetic coupling should prevail, there is an easy and relatively inexpensive way to use physical coupling in addition to the LSM magnetic coupling of cars on the guideways.

An entering car will join an existing guideway platoon at the front, at the back, or in a space provided by a car that has just left that platoon and exited the guideways or switched to another guideway. Vacated spaces will be of several standard lengths since all guideway vehicles will be built to one of several standard lengths. All platoons can consist of cars of assorted lengths. The computer will have the length of each vehicle in memory from the car identification data that it read when the cars entered. So the exact length of each gap in a platoon will be known, and the merge computer will wait for the right length gap to arrive for the car wishing to merge, or it will place that car at the front or the rear of a platoon. A merging or demerging car will shift almost purely laterally with respect to the synchronized vehicles on the guideway. With all of these things in mind, please draw a mental picture of the following, to save me the trouble of making a sketch.

To provide mechanical redundant coupling the rear of each car could be fitted with the equivalent of a trailer-hitch ball. The front of each car would have a special hitch socket. A conventional trailer hitch is engaged by lowering the trailer tongue. To engage couplings between the dualmode cars we could instead use the lateral shift during merging. The sockets would then need to be a little wider, and open on both sides. A merging or demerging car would automatically connect to or disconnect from the car ahead and the car behind, while maintaining its own synchronization. No lateral restraint would be required in the coupling since the guideway will keep the cars in line.

One might compare this random gap-forming and refilling in a platoon to removing a bottle from a line of bottles on an operating conveyor belt, then filling the resulting gap with another bottle of the right size a little farther down the line. The person putting in the bottle will synchronize its speed with the speed of the belt, just as the guideway-merging computers will.

But forget mechanical couplings—they won't be needed. It will be much more logical, less expensive, and probably safer to get guideway users to trust the LSM system. Travelers have had to learn to trust every new transportation system in history. Dualmode guideways will be no more difficult to accept than trains, automobiles, or airplanes were.


Last modified: July 24, 2001