A retroreflectivity measurement system comprises a light source arranged to project light across a traffic lane during a measurement run, the light being limited to a particular portion of the visible light spectrum. A camera is selectively sensitive to this light to provide first filtered images and separately selectively sensitive to light at a portion of the spectrum not including the particular portion to provide second filtered images. A controller obtains sequences of first and second filtered images during the measurement run, and identifies within the sequences of images an illuminated road marking; determines a first intensity of the marking from a first filtered image, and a further intensity of the marking from the second filtered images; estimates an ambient intensity of the marking, by applying a scaling factor to the further intensity; and determines a retroreflectivity of the marking as a function of the first and estimated ambient intensities.