Continuity mistake: After Manny's fingers get crunched between the cars, blood sprays on his face. In the next couple of scenes there is hardly any there. Also, when the prison warden get sprayed with the fire extinquisher he is cleaned up in the following shots.
Continuity mistake: When you first see the freight train that eventually would get its caboose smashed, the locomotive is a big one with lots of snow on the front. In all the other shots of this train, it`s a smaller locomotive, and it has no snow on the front.
Continuity mistake: Almost at the end of the movie, Warden Ranken is trying to board the train hanging from a ladder of a helicopter, and Manny is yelling to him through the right windshield of the second locomotive, the old F7 streamliner. If you look closely when the camera shoots from the inside of the loco and forward through the windshield, you will see that the first engine is gone. (01:34:00)
Continuity mistake: Before and while the train crosses the bridge, the words "Alaska Railroad" at the top of the tunnel portal at the start of the bridge appear and disappear between shots.
Continuity mistake: When the guard lets Buck in the gate to get on the elevator, he is holding the keys in his right hand. As Buck is giving the guard the shoes, the keys are in his left hand.
Continuity mistake: The F7 (2nd locomotive) has a unique snow plow mounted on its front, but the miniature replica used for the freight train collision scene wears no plow at all. (00:48:20 - 01:03:00)
Continuity mistake: After the accident with the caboose, we see some inside shots of the first locomotive showing lots of debris from the caboose having penetrated the windshield. But in the outside shots, you can see that there are lots of debris on the front of it, but the windshield is intact.
Continuity mistake: After colliding with the tail end of the freight train, Manny looks forward along the right side of the runaway train and announces that all the hand rails are gone (torn off in the collision), yet for the rest of the film, all the hand rails on the right side of the locomotives are present and undamaged. The left side of the train (the side that has much more contact with the freight train in the collision) is never seen again in the film, presumably to suggest that is the side that lost its railings, which explains the twisted railing debris between the locomotives seen when the characters are moving between them (along the right sides). (00:48:00)
Continuity mistake: When Manny first sees the train they're going to board, they walk a short distance alongside the train as it's moving. Pay attention, and you will see that the second locomotive, the F7, is missing. The first locomotive is now coupled to the third locomotive, even though the F7 was there in the shot before and is back in the next shot.
Continuity mistake: When Warden Ranken first goes to see Manny in his cell, he is walking down a prison corridor with prison cells on the left side of the camera and the prison wall on the other side. And when he is coming back from Manny's cell, he is coming down the same corridor. The problem is only that he is going the same direction as he was when he was going TO Manny's cell.
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: Ranken's helicopter alternates between two registration numbers: N20401 (small font on the bottom of the chopper's main body, ahead of the skids) and N710GW (covers the entire bottom). (01:32:20 - 01:33:15)
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.
Chosen answer: Most likely from the speed at which the train was going, a train is like driving any large vehicle. You have to maintain a certain pace, to stop at an instant, for the unexpected.