Films I've recently seen involving trains :
Horror Express. Hammer regulars Peter Cushing and Christopher Lee have to chase down a brain-sucking body-hopping intelligence on a trans Manchurian express in the 1890s. The film was written just because there was a model train and some carriage sets left over from a couple of other films. It can be found on YouTube. As an aside, so can The Iron Mule, a silent that reused the train built for Our Hospitality.
Dread Poets society: Benjamen Zephaniah and Timothy Spalls ' train journey from Birmingham to Cambridge during the sectorisation era is interrupted by a bunch of hooligans off their heads on laudanum or something. Worth a watch for anyone missing the power and the might of British Rail. Again, it's posted up on YouTube.
Split Second: Nothing at all to do with trains but the climax takes place in a flooded tube station on the Circle Line (that sort of attentions to detail). Probably one to watch through your fingers as a waterlogged Standard tube stock train (or earlier) gets used as a scratching post by a serial killer who thinks he's Satan and manages to be both psychotic and psychopathic at the same time apparently. Rutger Hauer, Kim Cattrell, Ian Drury , Pete Postelthwaite and Alun Armstrong as da chief.
As for whodunnits on trains where the villain isn't a satanic gene-stealing thingy from out of space, Poirot in the form of David Suchet has investigated murders on the Plymouth Express and the Blue Train as well as been in the best version of Murder on the Orient Express imho. Joan Hickson s' Miss Marple was the best version of 4:50 from Paddington again in my opinion, and the recent TV version of The Lady Vanishes was a good one (purists might prefer the first version because Hitchcock).
One of Hitchcock s' early films was Number Nineteen? ,it ended with a train vs. bus chase ending up at the folkstone train ferry. All done by model work.
As opposed to Terror by Night, one of the Basil Rathbone Holmses, where the London to Edinburgh express was represented almost entirely by stock footage of almost anything. This is rotation on Talking Pictures fwiw.