Wet Night Visibility of Pavement Markings

Thirty-three participants, all 60 years of age and older, evaluated the visibility of six different pavement marking materials under a simulated rain system operating at 0.8 in. (20 mm) of rain per h at night. Evaluation consisted of counting the number of skip lines visible from both a sedan and truck tractor, under headlight illumination only. Participants also evaluated markings from the sedan under dry conditions at night. Visual observations were compared with measured retroreflectivity of pavement marking materials, measured luminance of pavement marking materials at 30 m, and calculated retroreflectivity at 30 m, on the basis of measured luminance and illuminance provided by vehicle headlights. Data showed a high degree of correlation between the visibility distance of a marking material and the log of both the measured retroreflectivity and the calculated retroreflectivity. A definitive level of retroreflectivity required to meet drivers’ needs in wet night conditions was not found in the investigation and is now the subject of further study. There was also a high degree of correlation between measured and calculated values of retroreflectivity under simulated rain and measurements with the use of two current ASTM test methods, E2176 and E2177. In a second experiment, six original participants evaluated the visibility of the pavement marking materials for a 10-min interval following cessation of simulated rain. Results of the second experiment indicated significant differences in the time required for the visual performance of a pavement marking material to recover from rain for paint and bead products versus that of other pavement marking materials under evaluation.