Modeling and calibration of large scale system dynamics mod - els : the case of the ASTRA model

Though the size of System Dynamics models should be compact focusing on the main feedback loops determining system behavior one kind of model can become quite large: multi-national, multi-sectoral spatially differentiated models. The paper briefly presents such a model called ASTRA (=Assessment of Transport Strategies), which is developed in several versions over the past eight years. The purpose of the paper is to describe an approach how such a system dynamics model despite its size can be calibrated to make it applicable for Europeanwide policy analysis of transport policies. The approach is designed as a sequential process involving an automated tool combining a C++-coded steering programme with the Vensim optimizer to enable calibration of large numbers of similar equations that only differ by their parameterization.