Revealing mistake: During the opening credits, it is obvious that the train is just a model during the initial close up shots.
Suggested correction: There is nothing in the opening shots that betray it as a model shot. Logic alone argues against it. Why would they go to the expense of building a detailed model when there is no unusual action or angles required? Especially since many of the shots are obviously not a model. Exactly how is it obviously a model?
I agree it does look like it's a model train, but that's only because of the filming techniques that make it appear to run a little choppier like it's was a light weight model. But it's real, for example in one scene that looks like it's a model, you see a real bird flying on screen.