Field Test of a Portable Retroreflectometer for Retroreflective Raised Pavement Markers

Abstract

The results of an evaluation of a portable retroreflectometer used to monitor the reflectivity of retroreflective raised pavement markers (RRPMs) installed at field test sites in Texas are presented. The correlation achieved between field and laboratory readings of RRPM reflectivity is described, and the degree of correlation achieved as a function of marker type and amount of reflectivity available is explored. Six different RRPM manufacturers provided a total of 17 different types of markers for evaluation. Over 2 years the retroreflectometer achieved an aggregate correlation value of 0.938 with the Texas Department of Transportation (TxDOT) laboratory measurements. However, the degree of correlation was not identical for all types of RRPMs. Whereas the correlation coefficient exceeded 0.90 for 13 of the 17 markers tested, coefficient values of only 0.755 to 0.852 were achieved by the other 4 marker types. In addition, the correlation between retroreflectometer and laboratory data was not necessarily consistent over the entire range of reflectivity values examined. Instead, the retroreflectometer achieved a lower correlation coefficient with the laboratory data at higher coefficient of luminous intensity (R_I) values (greater than 148 mcd/lx) than at lower R_I values (less than 148 mcd/lx). Nonetheless, the evaluation indicated that portable retroreflectometers have improved sufficiently that TxDOT now is confident using them to determine compliance with specifications.