Thinking more on it, I realized that trains/convoys don't leave their respective starting locations any more (I think they ran the whole route in AHI, or at least spawned from their starting point and ran to the little shack before popping up at the little shack on the other end). Now-a-days they simply spawn at the shack at the end of the road leading out from the field/factory, but the idea behind it is that they're coming from the above places.