Many impedance models can be used for describing the acoustical behaviour of a road. These models rely on some intrinsic parameters (2,3 or 4), which are difficult to measure in the field. Therefore, the measurement of these parameters usually requires to destroy the structure. This is not always a good way to caracterize these parameters, because first those are only measured in a very local area, which may not have a global meaning, and secondly the way of building and the evolution in time of the road are not taken into account. The present paper deals with numerical simulations based on Simulated Annealing in order to set up a method for road acoustical parameters identification. The main idea is to consider any pavement, to make in situ acoustic impedance measurements and from these experimental data, to retrieve the intrinsic parameters of the road.