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.
Computer models like CARVE (Computer Aided Roadmarking Visibility Evaluator), which predict the nighttime visibility of pavement markings, require quantitative information about the coefficient of retroreflected luminance RL for selected pavement marking material and selected dimension parameters. To specify the coefficient of retroreflected luminance RL, four angles are necessary (observation, entrance, presentation, and orientation). However, RL values for pavement marking materials are measured as a function of two angles only, whereas the other two are held constant. This two-angle–only approach makes the RL data-collection procedure and subsequent computer models significantly less cumbersome. The objective was to determine the angleranges in real-world driving situations for the International Commission on Illumination’s goniometer, intrinsic, application, and roadmarking four-angle system to measure RL values of different pavement marking materials for sets of the observation, entrance, presentation, and orientation angles and to compare these RL values with RL approximations calculated by using two-angle intrinsic and roadmarking angular systems. RL approximations using the two-angle intrinsic system (based on observation and entrance angles only) overestimate the actual RL values by between 4 and 10 percent. On the other hand, the RL approximations based on the two-angle roadmarking system (taking into account only illumination-elevation and the observation-elevation angles) overestimate the actual RL value by between 25 and 82 percent. Under retroreflective conditions, it is suggested to use the two-angle intrinsic system rather than the two-angle roadmarking system for modeling pavement marking visibility problems because the abridged intrinsic system yields more accurate and more conservative RL approximations.
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