Ok, I'll try to do some math. A train like the
ICE 3 weighs about 400 tons, is 200 m long, and has a capacity for 460 passengers. According to
this article, the ICE 3, commissioned in 2012, should have regenerative brakes. Usually the efficiency is up to 17%. Fortunately I don't have to calculate this all by myself, as Dave mentioned in his video, the ICE 3 needs
59 Wh / seat / km.
Here is a train which runs with a rope. The 3rd generation has a capacity for 100 persons and weighs 12.5 tons. This is just a real world example how light a train can be for a given number of passengers, if it doesn't have motors. So use 5 of it, and you could transport more persons than with the ICE 3, but it would weigh only 62.5 tons, 1/6 of the ICE 3. Could be less with modern materials, but might need more, if it runs faster for more stability, and for more comfort, say 100 tons. The 300 tons weight difference is plausible, because a big locomotive can weigh 200 tons, and the ICE has distributed the motors over the wagons, which I guess increases the weight. 500 passengers might weigh worst case additionally 50 tons. To accelerate 150 tons to 320 km/h, you would need at least 591 MJ for the air train (1/2mv^2). To accelerate the 400 tons ICE to 320 km/h with additional 50 tons passengers, you would need 3 times more energy, at least 1.77 GJ.
I guess the loss because of friction is lower as well with the air train, because it is lighter. But let's assume the same as for the ICE, because of the additional friction of the piston mechanism. Breaking could regenerate energy as well, just close a valve at the other side and use the air pressure to power a turbine. And efficiency could be higher because of stationary motors and generators, but assume the same. Then it could be 3 times more efficient than an ICE. But I think this is a very conservative calculation, because the piston mechanism gives it more stability, so the required weight might be reduced even more (they added extra 1.5 tons masses in the floor per wagon for the ICE to increase stability with strong side winds).
Of course, I know nothing about mechanics, and it would need some serious new inventions and tests (graphene tube
), and maybe it doesn't scale to ICE size like trains, but in theory it could be more energy efficient, just because of less weight, that's basic physics.
PS: For a typical distance between two stations of say 50 km, and if the ICE 3 accelerates to 320 km/h, and with the theoretical minimum energy of 1.7 GJ, it would be 74 kJ / seat / km, so 20 Wh / seat / km. About 1/3 of the 59 Wh in the study, so I guess efficiency of the motors and the regenerative brakes might be not that good, and the friction, wind resistance etc. needs energy, too. But still pretty good, and it shows that the numbers are plausible.