Here's how you test how far you can move via rail without paying a cost in rail cap. Pick a unit on the rail, that
hasn't moved yet and therefore can embark on the train and embark it. DON'T MOVE IT. As long as you don't move it
you can still disembark it again. So then trace your mouse cursor over the rails in the direction you'd like to go
and the AI will find the furtherest path there is for that unit. And then you can disembark the unit and carry on
with your moves.
