There seems to be alot of debate about whether the train was just a coincidence. Well it could have been and the great thing about art is it's something different to everyone who watches it. Let me point out the FFC has a degree in Film and English and would be well versed in metaphors and allegories and the like. Mario Puzo is a writer so I do think the Train does have strong metaphoric properties as well as perhaps symbolic of Michael's mind and even perhaps a way of muffling the shots.