RETROREFLECTIVITY REQUIREMENTS FOR PAVEMENT MARKINGS

Subjective evaluations by 59 observers and quantitative measurements of in-place roadway markings were made in order to determine minimum field luminance and retroreflectivity levels for pavement markings. A minimum luminance value was also determined for the same observers through subjective evaluations and quantitative measurements under controlled and repeatable laboratory conditions. For the field test, more than 90% of the subjects rated a marking retroreflectance of 93 mcd/sq m/lx as adequate or more than adequate for night conditions. More than 98% of the subjects rated all locations having a marking luminance of 3.84 cd/sq m or greater as adequate or more than adequate, corresponding to a measured retroreflectivity of 94 mcd/sq m/lx. For the laboratory study, more than 90% of the subjects rated the simulated markings with a luminance of 0.38 cd/sq m as adequate or more than adequate. Subjects used in this research represented a relatively young population, and the study was conducted under the ideal field conditions. It is likely that an older driver, operating in a real-world driving situation, would require a retroreflectivity value higher than 93 mcd/sq m/lx.