I am not sure if you are referencing that or something else, but in Fallout 3, due to limitations of the engine, the moving trains in one of the DLCs were made as follows: there has been a head equipment item with a model of a train that was put on the heads of NPCs, themselves buriend in the ground, that were then made moving with the appropriate speed - NPCs were about the only thing allowed to be dynamic in the engine.Now all you have to do is fit it around the players head.