Relative Luminance of Retroreflective Raised Pavement Markers and Pavement Marking Stripes on Simulated Rural Two-Lane Roads

The FHWA Turner-Fairbank Highway Research Center is undertaking a research program to study the visibility of retroreflective raised pavement markers (RRPMs). The focus of the initial effort is to determine the relative luminance of RRPMs and pavement markings (PMs) needed to produce adequate guidance on rural two-lane roadways at night. A driving simulator was used to test 36 research participants as they drove simulated roadways containing various combinations of RRPMs and PMs. The luminance of the simulated roadway delineation ranged from 0.07 to 4.1 cd/m2. The primary driver performance measure was curve-recognition distance. For the various RRPM and PM luminance conditions, mean curve-recognition distances ranged from 19.0 m (62.3 ft) to 68.4 m (224 ft), with a grand mean of 43.0 m (141 ft). Regression analyses produced predictive equations to estimate the mean curve-recognition distance from the luminance of RRPMs acting alone or of PMs acting alone. Trading ratios were computed for PM luminance with and without RRPMs present on the road. A conservative empirical estimate of 0.52 was computed for such a trading ratio based on the data from the current experiment. This value compared favorably with independent estimates of 0.54 and 0.55 based on an earlier analytical approach. Thus, the current experiment confirmed, with empirical data, earlier estimates that it might be possible to reduce the luminance of PMs on rural two-lane roads by about 45% when appropriate RRPMs are installed.