Pooh has it right. No need for a city-wide food bank. Surplus food is distributed each turn - through what ever mechanism - and food that goes to cities can either be stored there or increase the population. I'll say a few words on the mechanism, though. I would just make it simple; no sharing food until refrigeration and then only within the RR network. It also makes it a more dramatic shift to urbanization, really changing character of the cities in a way that civ glosses over now. Functionally we're splitting hairs, because the spoilage factors should be really high pre-refrigeration and RR, and very small there after. Being an huge econ nerd, I love the economies of scale and diminishing returns to factor production. However, I don't see the game-play enhancement here. I know I had a relatively complex econ post up recently, and I like the stuff - but some corners would need to be cut in implementation - and this might be one of them. I love the idea though - but it does make tile optimization more complex for players who do not wish to automate it, so it might not be a worthwhile trade off.