A couple of things, in the real world, a 20 foot container is not really a commodity, except for the limited industries which build them. Rather, they are substitute vehicles into which one loads other commodities for transport. So, an industry which receives raw materials in 20 foot containers, and ships finished product might very well use those same 20 foot containers. So, in the more restricted world of Trainz, where in order to be loaded on a freight car, an item has to be a "product", 20' containers are "products". And there are other cases in real life of industries which both receive and ship the same product. Warehouses, for example, where a company might store finished product while awaiting shipment to the final customer: these industries receive and ship the same product, too. In fact, any sort of collection or distribution enterprise receives and ships the same product.
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