The quality of a pavement marking is measured in relation to night and day visibility. Luminance contrast between marking and substrate is very important. Contrast sensitivity of the eye varies with its level of adaptation and it is best to consider both day contrast (CJ) and night contrast (CN) values. CJ, CN and retroreflected luminance RL were studied in 33 test zones using ECODYN equipment. 52 observers in 26 vehicles were used. Observations were made in October 1994 during a clear day and at night. Observers had to indicate whether they judged visibility of markings "acceptable" or "unsatisfactory". The mean values of RL, CN and CJ for the 33 zones were 282 mcd/m2.lux, 13.7 and 1.4 respectively. Comparison of observers' responses with measurement results yields some useful information. Isolated markings are less visible than grouped markings between lanes. Requirements for isolated markings should therefore be higher. Above a certain day contrast threshold, measured under an overcast or sunny sky, observers overwhelmingly regard markings as sufficiently visible. This threshold is approx 1.2 for the 3.5/4.5 degrees geometry. When change is made to 1.24/2.29 degrees geometry, threshold would be approx 0.6. This suggests that in diffuse illumination, as angle of observation decreases, luminance of markings decreases faster than luminance of the surfacing.
Abstract