North West Frontier - starring Kenneth More set in India. Great film - crossing the partially blown up bridge was very well filmed.
Unstoppable 2010 - which is supposed to have been inspired by real eventsin the USA. - Actually saw this at the cinema which was unusual for me as I don't go. But back then when I was teaching we used to have a Christmas trip to the multi Screen cinema near the school and Unstoppable had just been released and I suggested that as one of the films and I volunteered to supervise that group. Great film, children enjoyed it and so did I.
There may have been a few technical inaccuracies but I recall is that the children were engrossed none asked to leave to go the toilet a well known request in class or elsewhere if they are losing concentration!
I see that 39 Steps has been mentioned - personally I rate the Kenneth More version as the best railway and acting wise - the original Robert Donat version is spoilt by the fact the LNER train briefly becomes Castle or King hauled as it emerges from the tunnel whistling at the moment the woman screams on finding the body in Hannay's flat. That one error spoils it in my book.
There is also the Ghost Train written by Arnold Wrigley (Private Godfrey in Dad's Army) there are two versions 1931 and 1941 (latter with Arthur Askey) filmed on the GWR in West Country and Wales - Barmouth Bridge features in the bridge scenes. If I recall the GWR Publication "Track Topics" which was republished in the 1970s included something on the making of this film, though long since lost my copy and can't check.