Continuity mistake: Towards the end of the film, in the control room, as the guys are arguing about what to do, the man sitting at the computer terminal is wearing a sweater over his shirt and a black watch. The older man says something, then goes over to the terminal, but now the guy's sweater is off and his watch is in front of him on the desk.
Continuity mistake: When Signal Maintainer 40 opens the door to the truck while Barstow is trying to reach him over the radio, the wind is howling so loudly. However, a few seconds later when he goes to sip his coffee and hears the train whistle, he rolls down the window to listen and there is no wind. Then, when Barstow commands him to "line her through," he opens the door and the wind is howling again.
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.
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.