In the framework of PROMETHEUS, Renault, Thomson et PSA have launched with the support of the French Government, the study and the development of a communication system allowing data transmission between a cluster of vehicles.

After having described the traffic circumstances where such transmission migth improve driving safety, the paper will describe the main features of the system, which can accomodate up to one hundred vehicles without any need of central management or synchronization, and will give the first results of experiments.