Keywords: cyber-physical, model, object-oriented, railroad, simulation, language.

Today, the term cyber-physical modelling systems refers to models which combine control and controlled systems. These models are very useful, since they closely reproduce the architecture of the systems to be modelled: the "cyber" part is the control system; the "physical" part is the controlled system. Modelica is a standard language for modelling systems in a cyber-physical way. Its usage brings the additional bonus of being a standard, and therefore models can in principle be run by any Modelica-capable tool. Modelica is conceived from the ground-up to allow hierarchical description of systems, and hybrid continuous-time or discrete time simulations. Finally, Modelica comes with a large library of validated models. This paper shows how the favourable characteristics of the Modelica language can be exploited to create powerful, flexible models of railroad vehicle systems. The special issue of the specific running pattern of railroad vehicles is addressed using a state machine. The special issue of the ever changing topology is dealt with the usage of variable resistors and a "commutator" model specially created for this application. The validity of the proposed techniques and the main physical effects simulated are shown.

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