Single- and multi-objective optimization problems in urban two-echelon networks

Increasing urbanization as well as the rapidly growing e-commerce sector contribute to increasing freight volumes especially in urban areas. On the one hand these goods contribute to our high standard of living, but on the other hand transporting these goods has negative effects on the environment and climate as well as on health and quality of life. These are major challenges today’s urban logistics has to respond to. In the field of city logistics, numerous methods are discussed, as for example the use of environmentally friendly vehicles to reduce emissions or the consolidated transport of goods from intermediate storage facilities to the end customers to reduce the number of freight trips in urban areas. However, convincing companies to adapt or change their urban distribution networks requires models which can be used as additional decision support. Therefore, this doctoral thesis contributes to city logistics modeling by investigating optimization problems in two-echelon urban networks. The papers of this thesis deal with mathematical models and metaheuristic solution procedures of two-echelon vehicle routing problems with customer deliveries on both echelons and synchronized meetings between different types of vehicles. All models and settings are tested on a set of instances. First of all, insights into the additional cost of synchronization are provided. Then, the impact of travel time uncertainties on the deterministic solution and the mitigation of this impact by reoptimizing the original solution based on information provided by simulated travel time scenarios is considered. Finally, the trade-off between costs, emissions and disturbance as the negative social impact on citizens caused by noise and congestion is considered in a multi-objective two-echelon vehicle routing problem. All these findings can thus serve as decision support for stakeholders who think of integrating alternatively fueled vehicles in their urban logistic chains.