This paper deals with the issue of using multi-cameras for road traffic monitoring. The aim is to remove the classic monocular ambiguities and to retrieve the objects height. An efficient and simple calibration method is presented. It relies on the geometric constraints of the road. A high speed matching procedure is introduced. It is based on an altitude planar decomposition of the road scene. The method naturally achieves two tasks due to altitudes sampling. Match and reconstruction become simultaneous. Finally, experimental results are presented.