According to an explanation at TAPCO traffic and parking control company, glass beads are used for adding reflectance to traffic paint on highways and roadways to make the stripes visible at night. The beads are added to the paint film after it has been applied. While the stripe is still wet the beads are broadcast onto the surface of the film.
The reflective coating you see on traffic signs, guardrails, construction barriers and other vertical surfaces is actually a reflective vinyl made by companies such as the 3M Company.
making a small donation to science.ca.