If the train is elastic, you'd recover that energy. Going into a curve, kinetic energy from the speed of the train is turned into spring energy by bending the

If the train is elastic, you'd recover that energy. Going into a curve, kinetic energy from the speed of the train is turned into spring energy by bending the train. Leaving the curve, the spring energy becomes kinetic energy. The flexed train speeds up due to the spring force as the train unflexes.