Vehicle Routing And Scheduling Models, Simulation And City Logistics

Abstract

The distribution of goods based on road services in urban areas, usually known as City Logistics, contributes to traffic congestion and is affected by traffic congestion, generates environmental impacts and incurs in high logistics costs. Therefore a holistic approach to the design and evaluation of City Logistics applications requires an integrated framework in which all components could work together that is must be modelled not only in terms of the core models for vehicle routing and fleet management, but also in terms of models able of including the dynamic aspects of traffic on the underlying road network, namely if Information and Communication Technologies (ICT) applications are taken into account. This paper reports on the modelling framework developed in the national projects SADERYL-I and II, sponsored by the Spanish “Direccion General de Ciencia y Tecnologia” (DGCYT) and tested in the European Project MEROPE of the INTERREG IIIB Programme. The modelling framework consists of a Decision Support System whose core architecture is composed by a Data Base, to store all the data required by the implied models: location of logistic centres and customers, capacities of warehouses and depots, transportation costs, operational costs, fleet data, etc.; a Database Management System, for the updating of the information stored in the data base; a Model Base, containing the family of models and algorithms to solve the related problems, discrete location, network location, street vehicle routing and scheduling; a Model Base Management System, to update, modify, add or delete models from the Model Base; a GIS based Graphic User Interface supporting the dialogues to define and update data, select the model suitable to the intended problem, generate automatically from the digital map of the road network the input graph for the Network Location and Vehicle Routing models, apply the corresponding algorithm, visualize the problem and the results, etc. To account for the dynamics of urban traffic flows the system includes an underlying dynamic traffic simulation model (AIMSUN in this case) which is able to track individually the fleet vehicles, emulating in this way the monitoring of fleet vehicles in a real time fleet management system, gathering dynamic data (i.e. current position, previous position, current speed, previous speed, etc.) while following the vehicle, in a similar way as the data that in real life an equipped vehicle could provide. This is the information required by a “Dynamic Router and Scheduler” to determine which vehicle will be assigned to the new service and which will be the new route for the selected vehicle