It only seems to happen in MP I've noticed. I'm not sure why it only happens in MP and not solo

found how to:

i did it, find safe-room broken door (will not close) center of the room be hole in the floor jump in> next step get (center area under the train) cliff side med-way up (yellow markers) need 3-fuel tanks (Tan or Brown in color) a man will drop them to you load them in compartments (under floor below the train) he'll drop next one, look below (silver tube lower train down) the train insert all 3 fuel tanks to fuel it up> then get on last train car (not engine), go in side door end of map! PVE Or Single player MOD

I was tuned to see if the doors open but it doesn't :(