In the "Specifics" section of this article, there is the following sentence near the end of the section: "And when a GVT train rises to the same elevation it had at the start, it recovers the gravity component of the down-slope energy at a delightful 100% efficiency." The statement that the train can recover 100% of the gravity component of the down-slope energy seems to violate the laws of thermodynamics. According to those laws, no system can be 100% efficient (meaning no system can recover 100% of energy expended), even when gravity is involved. For example, even if you were to put a simple pendulum in a complete vacuum, and the pendulum was using some sort of completely friction-less bearing, the pendulum would not swing forever. With each swing, some of the energy initially imparted to it as it began to swing down would be lost in the form of heat, so that on the upswing it would not reach the same height from which it was initially dropped during the down swing.
Furthermore, the statement in this article about the train recovering 100% of the gravity component of the down-slope energy has no citation, either.