The Iowa Department of Transportation (DOT) relies heavily on the performance of waterborne pavement markings in providing guidance to motorists. Waterborne markings are installed by DOT crews at the district level and cover roughly 95 percent of the state maintained system. The DOT is continually seeking opportunities to improve crew-applied waterborne marking performance in terms of durability and retroreflectivity. Specific to night-time performance, proper placement of the glass beads, within the waterborne paint, is critical to maximizing retroreflectivity (visibility back to the driver). One of the ways the DOT improved retroreflectivity was to improve bead placement through slowing their trucks down from around 14 mph down to 8 mph. With a limited painting season, and slower truck speeds, the DOT found it difficult to achieve their desired annual paint coverage. In an effort to increase application speed and yet achieve good bead placement (and resulting retroreflectivity) the DOT investigated the option of using a new style of bead gun. This paper presents the findings of a field study using two different (higher application speed) bead guns and reports on the contrast between the two devices in terms of bead delivery versus application speed.
Abstract