Models and Cuts for the Two-Echelon Vehicle Routing Problem
نویسندگان
چکیده
In Multi-Echelon Vehicle Routing Problems the delivery from one or more depots to the customers is managed by routing and consolidating the freight through intermediate depots, called satellites. This family of problems differs from Multi-Echelon Distribution Systems present in the literature. In the latter the attention is focused on the flow assignment among the levels only, while we also consider the fleet management and the overall distribution system routing. In this work we consider the Two-Echelon Vehicle Routing Problem (2E-VRP), the basic variant of Multi-Echelon Vehicle Routing Problem with one depot and a fixed number of satellites. First level routing manages depot-to-satellites delivery, while the second level deals with satellites-to-customers delivery. The main goal of this work consists in detecting and defining new classes of valid inequalities for strengthening the continuous linear formulation of the 2E-VRP. Starting from the flow-based model presented in [8], we first extend the model giving a stronger formulation for it. Secondly, several valid inequalities are presented, derived from the TSP and CVRP literature, the network flow formulation, and the connectivity of the network. Extensive computational results on instances with up to 50 customers show an improvement of the best known results between 4% and 15%.
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