1. A method of detecting vehicles on at least one stretch of a carriageway implementing: an acoustic detection comprising a step of acquiring and processing the sound originating from at least one zone, termed the acoustic monitoring zone, of the stretch of carriageway; and at least one detection chosen from: a video detection comprising a step of acquiring and processing the video images of at least one zone, termed the video monitoring zone, of the stretch of carriageway; a radar detection comprising a step of emitting a microwave electromagnetic radiation towards at least one zone, termed the radar monitoring zone, of the stretch of carriageway and a step of acquiring and processing the microwave electromagnetic radiation reflected; and comprising processing the results of the acoustic detection and at least one of the video and radar detections so as to deliver an item of information regarding the presence or absence of at least one vehicle; wherein each detection performs the acquisition and processing steps at a sufficient frequency to allow at least two acquisitions of a vehicle travelling in the monitoring zone at a given reference speed.