Abstract: A road surface illuminated by sunlight is scanned with a laser beam at right angles to the direction of travel, the intensity of the laser beam being intensity modulated with a predetermined frequency; laser beams reflected from the road surface are received and optically filtered to filter out light having frequencies outside that of the laser beam. The optically filtered laser beam strikes a plurality of beam position sensing elements from which respective electrical signals are derived. The resulting electrical signals are then multiplexed and electrically band-pass filtered wherein the center frequency of the band-pass filtering coincides with the frequency at which the laser beam is intensity modulated.