Plot hole: Had one or more locomotives coupled onto the real runaway's front engine, or even just been pushed by it, anyone aboard the "rescue" engine could have just walked to the unoccupied ones and shut them down - no copters or fireballs required.
Continuity mistake: In the scene when Train 777 is coming straight at the passenger train with the kids, the train is coming straight at them (just a single track). But a few shots later, a rip track leading to a siding comes out of nowhere without being seen. (00:23:05)
Suggested correction: The view at the single track is obviously not from the other train's perspective.
Factual error: In the yard when the air hoses are discovered to be not connected, the purpose of the connected hoses is to release the brakes, not apply them. With the hoses disconnected the brakes on all the cars are automatically applied.
Suggested correction: I'm a locomotive engineer. The air hoses have to be hooked up to apply and release the brakes. They are not necessarily applied if the hoses are disconnected.
They will apply if the gladhands disconnect en route.
Suggested correction: Not necessarily. Some engines may not have a rear cab access (like Frank/Will's engine had). And even if the rescue engine did have a rear cab access 777's engine only had a side access stair which at the speed it was going is more difficult to climb over from the engine in front of it.
Actually 777's catwalk goes across the front, from side stair to side stair, but someone would have to leap over a rail or a chain to get onto it from the other engine. Why would there be stairs on the right side unless there was a catwalk to get to the door on the left side?