Revealing mistake: Max's wheels can be seen moving backwards when he is actually driving forwards. Also, both Max and Monty's steering and wheel speeds are out of sync with their movements. These events happen throughout the episode.
Revealing mistake: When Samson crosses the Vicarstown Bridge, there is no shadow effect on his face.
Revealing mistake: The end of the set is visible in one shot at the quarry.
Answer: Breakdown trains help the engines back on track.