Membrane computing is an emergent branch of natural computing, taking inspiration from the structure and functioning of a living cell. P systems, computing devices of this paradigm, are parallel, distributed and non-deterministic computing models which aim to capture processes taking place in a living cell and represent them as a computation. In last decade, a great variety of extensions of model, introduced by Paun in 1998, were presented. In this paper, we focus on modelling the traffic flow by the means of P systems. P systems enable mezoscopic representation of traffic flow with individual modelling of each cars behaviour. Theoretical model is presented together with an XML scheme to store the output of the model.