Safety Evaluation of Permanent Raised Snow-Plowable Pavement Markers

Permanent raised pavement markers (PRPMs) often are used to improve preview distances and guidance for drivers in inclement weather and low light conditions. However, studies in three states in the United States have raised concerns about these devices after negative safety effects were found. To address these concerns, an NCHRP project was initiated to assess definitively the safety effects of PRPMs and to develop guidelines for their implementation, by using state-of-the-art methodology and a database from across the United States. This project evaluated the safety performance of snow-plowable PRPMs on two-lane roadways and four-lane freeways by using data collected from five states. The results show that on two-lane roadways selective installations in one state were accompanied by highly significant decreases in total, nighttime, and wet-weather crashes, whereas there was no apparent overall safety benefit for the nonselective installations in two states. A disaggregate analysis of those results found that the nighttime crash effects can be larger on higher-volume roadways and those with degree of curvature of 3.5 or less (radius larger than 500 m). On four-lane freeways, there were some positive indications for wet-weather, guidance-related, and nighttime crashes, with the effects for nighttime crashes increasing as traffic volumes increased. The results of the disaggregate analysis were used to recommend Manual on Uniform Traffic Control Devices guidelines for the implementation of PRPMs.