Yellow thermoplastic road markings with high retroreflectivity: Demonstration study in Texas

Road markings are a niche category of industrial coatings with requirements related to both the coating itself and the layer of glass beads on top of it that furnish retroreflectivity (RL) – their key property, particularly needed during driving at night time and in rainy weather conditions. The most frequently used glass beads, with refractive index 1.5, are capable of delivering RL reaching only about 400 mcd/m²/lx in white and 200 mcd/m²/lx in yellow markings; very low retroreflectivity under wet conditions, seldom exceeding 50 mcd/m²/lx can be obtained. Recently introduced ‘premium’ glass beads, with refractive index marginally increased, to 1.6–1.7, can yield more than twice as high RL. It was envisaged that high RL in a yellow road marking could be achieved if a structure with high vertical profile were reflectorised with these premium glass beads. Because of strict compositional requirements for road markings used in North America, a demonstration trial was made possible due to a special specification that allowed some departure from the fixed standards, but within new high-level demands related to RL under both dry and wet conditions. The tested material was a thermoplastic mass applied as regular dots that, due to round surface, would facilitate rainwater drainage, thus permitting the glass beads surface to be exposed to deliver adequete RL also under wet conditions. The performance achieved in the field was excellent: after 30 days, RL 894 mcd/m²/lx under dry and 160 mcd/m²/lx under wet conditions were achieved. Moreover, the applied road marking system maintained the required performance for 12 months (RL 774 mcd/m²/lx), while the control failed (RL