Seven road marking materials were investigated by optical measurements over a period of up to 22 months after installation of the markings. With the aid of all the measured data the properties of the various marking materials were described in terms of coefficients of retroreflective luminance and coefficients of luminous intensity, after which the corresponding visibility distances were calculated. The main factual conclusion is that the ultimate night visibility (at 22 months) of the commonly used paint lines and thermoplastic marking materials declines considerably on wet road surfaces. At that age, paint markings are hardly visible one minute after being wetted. Better alternatives are provided by vertically profiled edge markings and by reflectors placed in the carriageway, which are very similar to each other in performance. The coefficients of retroreflection of the newer types of marking, more particularly the profiled edge strips, are approximately ten times better than those of paint lines. However, because of the logarithmic response of the human eye to stimuli, this difference is less pronounced in terms of visibility distances. Road surface reflectors (reflecting studs) unmistakably retain their good reflecting properties under wet conditions. Night visibility does, however diminish considerably in consequence of dew on the reflectors. This report is also available as Mededeling Studiecentrum Wegenbouw SCW no 52.
Abstract