Run on premade, static tracks with clearly divided "roads" from the rest of road participants.

Their role is to stop the train in an emergency and adjust to speed etc. to track/driving conditions.

Automating their job probably wouldn't even need the complex ML used for self-driving because the context is significantly simpler and relatively well defined. Maybe a team in city might need such a model but it would still be a significantly simpler task than driving a car.