Pavement Marking Photometric Performance and Visibility under Dry, Wet, and Rainy Conditions

Abstract

Pavement markings are a fundamental component of the roadway safety infrastructure. They play an especially important role at night, when there are fewer visual cues for the driver. Although progress is being made in pavement marking management practices, advances in materials are still needed to fulfill driver needs for nighttime visibility and guidance under all weather conditions, especially wet and rainy conditions. This study was conducted to investigate the relationship between the photometric properties of pavement markings and their visual performance under dry, wet, and rainy conditions. For this pilot study four levels of material performance were created by a systematic reduction of the retroreflective efficiency of a single wet retroreflective tape construction. The nighttime visibility of the pavement marking materials was evaluated under dry, wet (just after rainfall), and rainy conditions. Eight 4-in. skip lines were viewed on the road in a standard 10-ft skip line and 30-ft gap pattern. The dependent measures were the number of skips visible, the subjective rating of the skip line relative to its adequacy for driver guidance, and average skip line luminance as a function of distance. Under rain conditions of 0.5 in./h, a material with an retroflected luminance in the rain ( RL-rain) of 30 mcd/m2/lux (per ASTM E2176-01) was found to provide an inadequate preview time and was rated as providing unacceptable visibility. A good correlation ( R2 = 0.94) was obtained for the instrumental measurement of RL and the number of skips seen. The luminance data suggest that an average pavement marking luminance greater than ∼0.5 cd/m2 is required for a skip line to be visible to the driver at night.