I think MS have effectively dropped their Train Simulator, but there is a huge amount of stuff out there. If I remember right, the models have to be made in gmaz format and then imported. If you can handle converting gmax to .obj you might be able to contact one of the creators and arange a test: in some ways it's rather like any other bunch of 3d enthusiasts. I think the models are pretty low-res, but some people did some quite detailed animation.