Many studies have addressed questions related to pavement markings; few, however, have dealt with the subject of minimum and generally acceptable retroreflectance values for nighttime visibility. Three studies that deal with this subject were found, and they agree closely on minimum and acceptable values. The question of minimum retroreflectance depends on the retroreflective quality of the painted line, the quality of headlamp illuminance, the contrast between the line and the immediately adjacent road surface, and the presence or absence of roadway lighting. Tests were conducted using markings with a broad range of retroreflectance on a level tangent roadway of weathered asphaltic concrete. A subjective system was employed for rating the lines, and the results correlated well with those of other studies. Two retroreflectance values, expressed as specific luminance in units of millicandelas per square meter per lux (mcd/m2/lx) are suggested as acceptable and minimum. These values are approximately 300 and 100 mcd/m2/lx, respectively. These values may be useful in establishing acceptance and service criteria for pavement markings. Theavailability of portable instruments such as the Ecolux, which was used in this study, permits the assessment of pavement markings for conformance to such criteria.(A).
Abstract