In this paper, we present an improved distribution plan for many urban distribution centers (UDC) as a solution to solve the last mile problem of urban freight. These UDCs have to meet daily demands for delivery on time of their allocated urban areas. However, these demands may not be met when they exceed the available capacities of these infrastructures. In addition, some UDCs are unavailable when their capacity to deliver is affected by random unavailability or preventive maintenance actions. In this case, the entire site or a part of it will be "Out Of Service".

Our goal is to improve the efficiency of these UDCs in terms of availability and satisfaction of demands and this via preventive maintenance actions as well as the inter-UDC collaboration strategy. For instance, unavailable UDCs can be delegated to others UDCs as a subcontractor to ensure deliveries for their allocated urban area on time. The choice of subcontractor will depend on distance, environment and availability criteria. In doing so, we define a mathematical model for searching the best distribution correlated to a maintenance plans using a subcontracting strategy for all UDCs. Moreover, we consider delay for the next periods with an expensive penalty. Finally, we present a numerical example illustrating the advantages of our approach.