From what I've read in other posts, if you resumed a saved session it might be bugged and you'll have to start all over again. The joys of scripted scenarios. Or it could be that you have to wait for another train that is in front of you. Real world you can often times be stuck at a red for quite sometime. Though I don't think TSW simulates long waits.
It doesn't happen very often, but when playing certain timetable services there are some that are more "interesting" in that you could be stuck at a red signal, or be following a stopping service meaning you'll have to be a bit more focused than usual. Especially if you are playing with active safety systems. So while it's not really simulated, it is a part of the timetables at least. See for example this thread.
