From streetlights to phosphors: A review on the visibility of roadway markings

•Roadway visibility has been a transportation topic of interest for over 100 years.•Traditional visibility techniques include: overhead lighting, glass beads in paint, raised markers, and embedded LED’s.•The very long lasting phosphor SrAl2O4:Eu2+,Dy3+ shows promise as an alternative lighting technique.•Phosphorescent paint must be optimized for paint stability and to protect it from hydrolysis. Roadway marking visibility has made substantial improvements since the beginning of the 20th century. The most common solution for increasing the visibility of road markings is the use of retroreflective beads, which suffer from decreased performance under wet conditions. To remedy this, alternative road marking visibility techniques such as luminescent paint have been investigated. A promising new technology involves the use of phosphors such as strontium aluminate doped with europium and dysprosium ions (SrAl2O4:Eu2+,Dy3+). This technology shows potential to be seen throughout the night. The two hurdles blocking the path for the use of phosphors in road marking paint are the need to stabilize the particles in the paint matrix, and the tendency of the phosphor to hydrolyze. In this review, an explanation of the science behind stabilization is set forth alongside several methods that show potential for mitigating hydrolysis.