The congestion of the motorway system in the peak hours involves a fall of the productivity for the conveyors, a waste of time for the motorists, an increase in the frequency and gravity of the accidents, thus a risk for the public health with the increasing of pollution due to vehicle gases. The aim of this study is the modelling of traffic congestion by multi agent systems. Agents are autonomous interacting entities able to cooperate in order to solve problems appears in traffic congestion such that: conflicts, incidents, synchronization. The behaviour of agents is described by means of coloured Petri nets.