Australia is the place. A train that relies on gravity is coming soon. The incident is simple. A very long train full of iron ore will see a total load of 34000 tons when it is loaded.
The electric engine’s batteries are charged while running. Regenerativebbreaking, which takes place several kilometers away from the factory, stops the train and helps to recharge the battery. So a journey like a swing on the shoulders of gravity avoiding fossil fuels.
Looking at Laws of thermodynamics and Laws of friction, it can never be argued that 100% of this energy can be recovered or that there will be a Prepetual motion here, but only a small beginning in the journey to make Gravity a terrorist. Suffice it to say.