Basically you have the choice between setting up complex traderoutes or use feeder service. I haven't tested them together, but I assume if you use feeder on a yield you manually set a traderoute to import, then that traderoute will forget it once feeder deactivates it and will not re-enable it once it starts importing again. Traderoutes focuses on a chain of colonies to visit in a specific order. Feeder service is made from the point of view from a colony which will not care where the yield comes from. The same setup with feeder service. A and B exports at 50. B sets feeder and C imports. Automated wagon trains will then take the yield from A directly to B or C. If B reaches 50, then excess is exported to C. B will then not import until it only has 37 left. Maybe C should have export too (but not feeder). This will allow C to transfer to B in case A decides to send everything to C. Remember that B will not accept anything from C unless it actually needs it. C will have no problem importing and exporting at the same time without feeder as long as it's the only one importing without feeder. The trick here is that you can have multiple colonies set just like B. Since they both import and export it will create loops, but the feeder will prevent them from importing and exporting at the same time, which breaks such loops. This means building a new colony allows you to set up import/export and it fits into the transport system just fine without looking at the other colonies or modify possibly fairly complex traderoutes. Manually setting up traderoutes will likely be the most efficient usage of wagon trains. However it does use a lot of micromanagement and which system to use depends on what you want from the game. I added feeder and any player can use it if they like. If not, they can still do just like in RaR as I didn't modify that system at all. Doing both in the same colony isn't recommended and will likely cause issues.