Laboratory-Based Retroreflectivity Assessment of Raised Retroreflective Pavement Markers

Abstract

Pavement markings are often supplemented with raised retroreflective pavement markers (RRPMs) to provide increased visibility, especially in wet nighttime conditions. To provide adequate visibility, highway agencies need to replace their markings and markers before they reach inadequate levels of performance. Currently, there are no quantitative visibility performance requirements for in-service RRPMs. Most markers are replaced on the basis of visual inspection or predetermined replacement schedules. This paper presents an initial investigation into the impacts of different measurement systems and different geometries on the quantitative evaluation of the visibility of RRPMs. A key question was how the different measurement geometries affected the retroreflective performance of RRPMs. The research found that when the observation angle was held at 0.2° and the entrance angle increased, the coefficient of luminous intensity also increased. This finding was true for every color and brand of marker for the geometries tested. There was a notable drop in performance when the evaluation geometry was changed from pavement marker geometry to pavement marking geometry. When the photometric range was used, the pavement marking geometry resulted in data that were 7.8% of the values from the standard marker geometry. Charge-coupled device photometer measurements resulted in pavement marking geometry results that were on average 6.7% of the value of the RRPM geometry. These values being close indicated that the two measurement types were comparable and that the markers could consistently be evaluated at the two distinct geometries.