The invention relates to a process for monitoring vehicles on a road by a system comprising at least one radar sensor and a second sensor different from the radar sensor, wherein the second remote sensor is a time-of-flight optical sensor or optical image sensor, the process comprising a temporal readjustment and a spatial matching in order to obtain a set of measurement points each assigned to first characteristics derived from the radar data and second characteristics derived from the optical data, the determination of the radar vehicle trackings and of the optical vehicle trackings, a comparison of similarity between the radar vehicle trackings and the optical vehicle trackings, the elimination of the radar vehicle trackings for which no optical vehicle tracking is similar, the process comprising monitoring a parameter derived from first characteristics of a retained radar vehicle tracking.