The flywheels had been used, for example, in gyrobuses

How about this, just implemented I think. Anything goes, isnt the Japanese bullet train with no actual physical contact friction in its movement the most energy efficient form of transport. At least for people, I dont know about heavy haulage maybe boats win on that one with diesel engines the size of buildings and their ability now to use the waste parts of oil cracking so Ive read is new tech available
