TRS06 or TS12? What operating system does your 'puter use? What 'Save' options have you tried - Save, Save As, Save route, Save session? What were you doing when Trainz crashed? Was it a 'controlled' crash (crash report screen present) or did it just bomb out? Did it crash all the way to the desktop or just to the Trainz menu? Did you install any new content just before it crashed? Were you placing new content on the route when it crashed?
I could go on with a zillion other questions, but the point is that to give any meaningful reply we need more to go on...