Pavement Marking Materials and Markers: Testing the Relationship Between Retroreflectivity and Safety

The objective of National Cooperative Highway Research Program (NCHRP) Project 17-28, "Pavement Marking Materials and Markers: Safety Impact and Cost-Effectiveness," was to develop guidelines for the use of pavement marking materials and markers based on their safety impact and cost-effectiveness. A key component of the research was the attempt to correlate the safety impact of pavement markings and markers with their performance, principally measured in terms of their retroreflectivity. If such a correlation were found, it would be possible to estimate cost-effectiveness and then develop the desired guidelines since retroreflectivity is a direct function of the costs of marking materials and their application. Thus, the project sought to test the null hypothesis that the safety impact of pavement materials and markers and their level of retroreflectivity are not significantly correlated. If the null hypothesis were rejected, it would be possible to conclude that greater retroreflectivity translates into greater safety, thereby justifying the costs of maintaining higher levels of retroreflectivity. A pilot analysis with the most comprehensive dataset available found that the null hypothesis was accepted: no statistically significant relationship was found between safety and the retroreflectivity of pavement markings and markers. This digest summarizes the final report of the project. It reviews the methodology used for the analysis of the data, its limitations, and key findings.