- The delivery trains would have only a single stop in their schedule: the drop-off station, with a departure condition of 'Empty cargo' OR '5s Inactivity'
- Each drop-off station would have a train limit of 1, and be disabled via circuit condition if the required amount of fuel/ammo/whatever was already present
- The delivery trains would also have a single interrupt: if 'Empty cargo' OR 'Destination full', go to the pickup station, with a departure condition of 'Full cargo'
However, on testing, I found that, while the 'go home if empty' part worked right, the 'go home if everybody is full' part did not; if all drop-off stations were full and thus disabled, any delivery train waiting at one would just sit there permanently.