Shippers can operate according to a schedule (line services) or on the basis of customers’ requests. Under the former hypothesis, at a tactical level, the shipper should assign the freight traffic, on the basis of the transport demand (which is known), to the network of existing transport lines (traffic assignment problem, or TAP, see Section 6.2). Conversely, when the transport network has not already been designed or when the existing one proves to be inadequate, the shipper should solve, always at the tactical level, a service network design problem (SNDP, see Section 6.3), on the basis of the forecasted demand or on the basis of commercial agreements stipulated with the customers. Under the latter hypothesis, at the operational level, the shipper needs to assign his owned fleet dynamically (and the vehicles hired eventually by other shippers) to customer requests, so that these are satisfied and the cost of using the entire fleet is minimized. At the tactical level, another decision making problem is the periodic repositioning of empty vehicles, so that the average response time to subsequent requests is kept as minimum as possible (vehicle allocation problem, or VAP, see Section 6.4). Other decision making problems for shippers are, at the strategic level, the composition of the vehicle fleet to purchase, and, at the tactical level, the optimal crew scheduling (a problem in this category will be dealt with in Section 6.5). Finally, at the operational level, decision making problems deal with the reassignment of vehicles and crews to take into account unexpected events, such as changes of the freight orders, vehicle breakdown, strikes or unfavourable weather conditions.