Continuity mistake: After the train operator gets his head dunked in the toilet by Warden Rankin, the poor guy has to wipe his face with tissue. The tissue disappears and reappears between shots. (01:17:13)
Continuity mistake: During the freight train scene, the runaway passes the same set of gondola cars twice.
Revealing mistake: When Manny goes to lay down and uncouple the two locos at the end, a 7" icicle is flapping in the breeze.
Audio problem: At the end of the movie, after Manny has disconnected the locomotive from the rest of the train which is slowing down, when it stops we can hear it screech. It shouldn't as the train slows down naturally without the help of the breaks, which additionally, as it had been mentioned (by the woman), are not working. (01:45:30)
Answer: That's what they were doing, going car to freight car break the hoses. They knew it would slow the train down but not stop it. Slow enough so they could jump off without getting injured. That's why they were desperate to get to the first engine not only to break the hose but disconnect from it.