Impact of Bead Density on Paint Pavement Marking Retroreflectivity

Abstract

This paper addresses the impact of bead density on paint pavement marking retroreflectivity. The writers collected retroreflectivity data and glass bead images on 40 segments of two-lane highways. Bead density is defined as the surface percentage of glass beads exposed above the paint marking material. Numerous methods for determining bead density were considered and studied. A new approach, referred to as a computer-aided counting method, was developed and a bead density analysis program was written. The program was used to analyze 108 images to obtain a bead density value for each image. A correlation study was conducted between pavement marking retroreflectivity and bead density. The findings of the study show that the normal range of glass bead density for older markings is 9–24% of the paint marking surface area. Furthermore, bead density values have a positive correlation with marking retroreflectivity readings; higher bead density leads to higher retroreflectivity. White paint markings have significantly higher retroreflectivity values than do yellow markings when the bead density values are the same.