Algorithms for network design and routing problems

Many practical problems arising in real world applications, mainly in the fields of logistics and telecommunications, can be modeled as network design or vehicle routing problems. In this thesis we study three combinatorial optimization problems belonging to the classes of Network Design and Vehicle Routing problems that are strongly linked in the context of the design and management of transportation networks. The problems considered in this thesis are the NonBifurcated Capacitated Network Design Problem (NBP), the Period Vehicle Routing Problem (PVRP) and the Pickup and Delivery Problem with Time Windows (PDPTW). These problems are interesting from both a theoretical and a practical viewpoint. They are inherently hard to solve since they all belong to the class of NP-hard problems and contain as special cases some well known difficult problems such as the Traveling Salesman Problem and the Steiner Tree Problem. Moreover, they model the core structure of many practical problems arising in logistics and telecommunications. The NBP is the problem of designing the optimum network to satisfy a given set of traffic demands. Given a set of nodes, a set of potential links and a set of point-to-point demands called commodities, the objective is to design the network topology, i.e., to select the links to install and dimension their capacities so that all the demands can be routed between their respective endpoints, and the sum of link fixed costs and commodity routing costs is minimized. The problem is called non-bifurcated because the solution networkmust allow each demand to