To evaluate traffic management policies and new in-vehicle technologies, a digital simulation environment can be useful for testing their functions in virtual experiments. This paper presents a methodology for building a traffic model in a microsimulation environment (SUMO) based on observed vehicular trajectory data. Applying an iterative process, the methodology to refine the traffic model is described to obtain output statistics consistent with observations. In particular, distributions of individual travel times and distances are comparable for most of the simulated and observed vehicles. The main errors detected during the model building phase were fixed, and the solutions adopted were detailed concerning vehicle route selection, traffic light setting, and manoeuvres modelling.