The invention relates to the detection of wheel axles of a vehicle on a roadway by means of a sensor, which operates according to the light-section procedure and emits at least one fan of light from a first location along the roadway to project a line of light onto the roadway and a vehicle possibly located thereon, and records this line of light from a second location along the same side of the roadway and detects a wheel axle as soon as the recorded line of light exhibits, in its course emanating from the said side of the roadway, a shift-free change in direction differing from its course when the roadway is empty.