Pros and Cons


Kim Goltermann

We begin with a horror story. The continuing story of the new Copenhagen Metro rail. When originally decided on, the first-stage budget was around 0,8 bn$ and the opening was set for October this year. So far the budget has swollen to 1,2 bn$ and the opening has been postponed 2 years. Furthermore is it uncertain if the driverless trains can ever have their safety systems approved. For political reasons it was also agreed that one end of the line should lead across an empty field, where a new city was planned to materialize. So far it hasn’t. Traffic is chaotic and the city resembles a building site, while shop owners are being bankrupted in the affected areas. The futility of traditional transit systems is so obvious that even politicians should be able to see it. I get very upset when I consider the wasted resources poured into these systems. We will have no more of them.

This contribution is a direct answer to Francis Reynolds’ call for a simple discussion of the pros and cons of various choices, and the personalized form is a consequence of this call. So here are some down-to-earth comments on some of the choices we would have to decide on, before we finalize the design of our upcoming dualmode system.

Francis, you concede that using pneumatic tyres on both the streets and the guideways "is certainly a cheap and simple way to go", but for numerous reasons already discussed you dislike them. I don’t know what these reasons are, nor can I imagine them.

Pneumatic tires are relatively cheap, and they usually lasts at least 30 000 miles (even longer on a smooth guideway). My latest set has carried me more than 40 000 miles so far and seems fit to go on for yet a while. Some modern pneumatic tires are capable of withstanding speeds well over 150 mph with excellent durability and trucks require even longer lasting tires to support their heavy loads.

For a modest price is it also possible to automatically monitor the immediate condition of pneumatic tires for wear, temperature and air pressure. According to a German research project I recently read about, by far the most common reason for exploding tires is wrong air pressure, not wear and tear as might have been expected. As a consequence a simple and cheap pressure monitoring system is currently being prepared for the market.

It is true that pneumatic tires have limited and somewhat unpredictable traction (friction) characteristics, especially if the road surface is wet or icy, but if tires are used only for support of the vehicle, the limited traction becomes irrelevant. This will be the case with the kind of LSM system I have suggested.

The energy efficiency of pneumatic tires are somewhat worse than for some of the alternatives (steel wheels, MagLev) largely due to the heat generating flexing of tires at speed. Flexing results in higher rolling resistance, but this is hardly crippling for the overall economy of our transport infrastructure in the dualmode era.

Rolling resistance is only one of many factors contributing to overall energy consumption in a transport system; aerodynamic resistance usually being the main culprit (more on that in a while). It is even a viable possibility to improve matters by using tires with variable air pressure. Relatively low pressure for a good grip on the road and higher pressure for less flexing/lower rolling resistance on the guideways.

So what is there to dislike about pneumatic tires, except their dullness? Pneumatic tires work. Guaranteed! About one billion people trust them every day. Just look out of your window to witness it.

You consider my proposal (including pneumatic tires and internal combustion engines) to be little more than an Intelligent Vehicle Automated Highway System (AHS) boosted with LSM for good looks. Nothing could be more wrong. The addition of LSM introduces a totally different control philosophy where positioning are controlled by system computers rather than by in-vehicle intelligence and sensors. LSM also allows much shorter headway than AHS, and most important, doesn’t depend on petroleum for guideway mode transportation. Finally LSM render the limited and unpredictable traction characteristics of AHS irrelevant. I will maintain that the kind of system I favour is essentially similar to the original HiLoMag concept (minus MagLev) having very little in common with AHS.

You also state that magnetic levitation and LSM can be an integrated package for little more than the price of either one alone. Maybe so, although I have read that levitation and LSM requires separate sets of magnetic coils, so I still doubt if you can have two for the price of one. My objections to MagLev originate in part from the fact that I don’t know enough about it. I have tried to read all I could find, but when things get very technical I usually bow out. So let’s see if I’ve got at least some of it right.

One of the biggest advantages of MagLev is that it promises to completely eliminate wear and tear, as there are no physical contact between vehicles and guideway. I have read about the passive MagLev technology Inductrack and maybe this new innovation can at last deliver the promised maintenance free operation, as the MagLev test tracks in Germany and Japan have so far been burdened with disappointing high maintenance requirements (not to mention ever escalating costs).

Another important advantage is the elimination of rolling friction, however this is replaced with some amount of electromagnetic drag. I haven’t been able to find any sources directly comparing those two, so it remains an open question which one is the smaller burden. I would, of course, expect MagLev to fare better than wheels when energy efficiencies are compared, as MagLev is often praised for its efficiency. MagLev also has unparalleled high-speed capability, and if properly designed it will also provide an incredibly smooth "ride".

If we levitate a vehicle, it will be necessary to provide some sort of power pick-up for on-board uses (heating, air-conditioning and maybe even propulsion). This can be either sliding contact or by induction. Either way it adds cost, complexity and increased maintenance. Far more serious is the problem of how to manage short-headway full-speed switching of a moving column levitated vehicles. The mechanical in-vehicle switch envisioned for the original HiLoMag concept doesn’t look promising. It is difficult for me to argue why, except that it would require costly and precise engineering to include failure proof 200 mph compatible mechanical switches on all dualmode vehicles. Maybe a better solution could be applied, more in line with the technique used by MagneMotion for their system, but adapted to levitation.

From the little I know about MagLev I feel that the balance is against it, considering an LSM/wheels combination can accomplish essentially the same. Even the Inductrack, which seem so appealing at first, face an uphill struggle as the cost could be up to 80% higher (for comparable track loadings) than already expensive conventional railroad tracks. However if someone could persuade me that my concerns over cost, complication, switching principles and maintenance burdens are unjustified, I could possibly be brought into line as a MagLev supporter. It would however require convincing arguments.

Could I possibly also be persuaded to favour a suspended-vehicles system? No way!

First of all because in all likelihood it precludes true dualmode (integral pallets - if you prefer that terminology), and I won’t compromise on that one. Even if it could be done, it introduces extra complication; how to align and connect the roof-mounted suspension with the overhead guideway. A heavy and bulky roof-mounted suspension will also impose severe limitations on car design, adding complication and cost to vehicles. And the suspended-vehicles guideways will be more visually intrusive than guideways for a supported-vehicles system, as they will need to be higher.

You discuss the problem of how to evacuate a guideway in case of a power outage or other problem. In a supported-vehicles system private cars would simply start their engines and drive slowly to the nearest exit, while driverless vehicles would require some simple back-up guidance system to get off the guideway under remote control. You suggest that suspended vehicles should be lowered to the ground with some kind of emergency winch (adding weight and complication), but have you considered all the practical implications of this idea. The area under the guideways would have to be reasonable level, no one could park their cars there and not even a bench or a hot-dog stand could be placed there. You certainly couldn’t allow guideways to cross water and for all practical purposes you would have to seal off all areas under the guideways, so that nothing were blocking in case you needed to lower vehicles from the guideways.

There seems to be no simple way to evacuate a suspended-vehicles guideway in case of an emergency, which is just one more reason to stick with a supported-vehicles system. In my opinion, when opting for a suspended-vehicles system you have also opted for a lot of trouble, even abandoning your original objective (true dualmode) just to gain some gravity-enhanced stability of vehicles. Is it really worth it to compromise everything for so modest gains?

Returning to the issue of high speed. No Francis, it is not written somewhere that a dualmode system should not try to accomplish certain things, but as you are trying to attract short haul air travellers with promises of high speed, I fear you could lose something much more important in the process. The huge freight market.

Freight is mostly transported with heavy trucks. Often the legal speed limit for these trucks is around 50 mph on highways, and if you consider the widespread use of smaller rural roads, highway congestion and speed reducing road works, the average trucking speed between cities are more likely around 40 mph (pauses not included). Freight trains are doing no better.

So what HiLoMag suggests is to replace our current 40 mph freight system with a new constant speed 200 mph system. This means that the average speed (between cities) will be five times higher, and all things equal, aerodynamic drag will thus be 25 times higher and so will the energy requirements to overcome this drag.

Unless you build expensive heavy-duty guideways, it will also be necessary to distribute the loads from the trucks on a higher number of vehicles. Maybe 5-10 small vehicles will be needed to replace one heavy truck, and this will make matters even worse as 5-10 small vehicles have a higher combined aerodynamic drag than a single large vehicle.

Yes, I know that electric propulsion (any) is more energy efficient than a diesel engine, and it helps to utilize aerodynamic drafting (short headway), just as constant speed will also reduce energy requirements. Rolling friction (for wheels) would of cause increase with higher speeds, while I’m a little uncertain about electromagnetic drag (for MagLev), but at high speed aerodynamic drag is the main contributor to energy consumption anyway, and your choice of small vehicles at very high velocities means that you will have to improve energy efficiency dramatically, just to obtain the same level of energy consumption as our trucks have today.

Something similar applies to transport of people, as the average highway speed of cars is around 65 mph. This implies an energy requirement, all things equal, of around 9 times present-day requirements if 200 mph dualmode is introduced. All in all, it doesn’t make much sense to talk of an impending energy crisis and then suggest alleviating it by putting all of our freight and private cars on the fast track.

A 200 mph dualmode transit system would consume exorbitant amounts of energy, and it would certainly push freight rates upwards, if such enormous amounts of energy could indeed be supplied. On the other hand; a good true dualmode system, meeting all your mentioned requirements save one (reduced short haul airline traffic), can be built without the complications of MagLev, suspended vehicles and high speed.

Note! The more I get involved with this subject, the more it appears to me that the biggest technological challenge of dualmode is the switching principle. How can we provide a simple, fail-proof, full-speed switch that can accomplish the switch function in a fraction of a second to facilitate short headway operation. The design of this switch will possibly also define the design of our guideway as well as other aspects of our much needed dualmode system.


Last modified: August 30, 2000