Plot hole: If Jack can speed the train up, why does he not try to slow it down? Even if it can't be stopped completely, using the speed lever to reduce it to the minimum possible would be a sensible course of action. There is nothing to suggest he wouldn't be able to do this as he is able to increase the speed without any trouble. If there was something to show that slowing down the train would be unworkable it would make sense, but seems to more serve as a plot device.
Plot hole: Soon after Jack gets on the bus, Howard can see the bus on the news. Why is the news at this stage covering this? The only thing that has been suspicious is someone from a car coming from a car onto a bus, but what has happened before this that makes this newsworthy? Looks like regular traffic is flowing up to this point. (00:44:00)oobs