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.
Plot hole: According to the channel 8 live report "the railway company is still not commenting." Yet they knew what happened to make 777 unmanned, that Dewey was the driver, his age, that he would face disciplinary action, that it was Ryan scott attempting to board, his age, that he was an ex marine, that he'd just came back from Afghanistan, that Judd Stewart was driving the front loco and his age, the names of Frank and Will and what they were attempting to do. That's an awful lot of accurate, detailed information when the company is apparently not commenting.
Plot hole: When they try to slow the runaway train using another train, the lead train slows to 40 mph but after the failed attempt by the military veteran to board the train, the lead train begins to increase in speed, eventually being derailed. The failed attempt and subsequent injury to the military veteran, although disappointing, would not have caused the runaway train to miraculously speed up, especially since the lead train was already capable of slowing down the runaway train down. (00:41:58 - 00:46:00)
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?