These are extensions of this work deserve further attention. We have already mentioned that our formulation assumes a “system optimum” for a world where each carrier (and shipper) is assumed to have ownership of the transportation infrastructure (as in the case of National Planning or City Logistics). A further extension of the problem could thus consider the case where the “central control” assumption does not hold, and where there are entities, either in coalition or competition, to serve the customer demand and carry out the freight transportation operations.