Other mistake: The episode's title in the original PBS Broadcast version is "The Old Iron Bridge" but the bridge was made of wood.
Snow Engine - S7-E14
Other mistake: Before Oliver crashes, no-one appears to be inside his cab in a shot of him passing a crossing.
Other mistake: When the narrator says that Duncan ran out of coal in the bridge, there is coal in his bunker.
Answer: He was in the water.