Microplastics and road markings: the role of glass beads and loss estimation

Road markings are often listed amongst meaningful contributors to pollution with microplastics. However, the reported estimates do not address the renewal frequency and its association with the key parameter of road markings - retroreflectivity. This parameter, achieved because of a layer of glass beads on the road markings surface, fails before the plastic-bearing layer could be abraded. Field and laboratory assessment indicated the presence of several layers of paint and glass beads, confirming that the road markings were renewed before abrasion could occur. A methodology to employ luminance histograms to estimate loss of road markings was developed and used to approximate the emissions at selected exemplary locations. The estimates indicated that road marking loss at the most used areas of pedestrian crossings was below 6%, which is much less than previously reported. Thus, the emissions of microplastics of any dimension from this source were calculated to be between 0.1 and 4.3 g/person/year (except in Nordic countries, where 56.3 g/person/year could be reached). Consequently, road markings do not appear to be as significant source of microplastic pollution as was reported before, except for specific local considerations.