dried to yield properly oriented lenses the retroreflective intensity of the inventive pavement markers having a retroreflective coating of spherical lenses has been measured at 0 677 candela foot candle of incident light 0 063 candela lux and a retroreflectivity coefficient of about 50 candela lux square meter cd lx m 2 this compares favorably to the 0 15 cd fc 0 014 cd lx and 0 566 cd lx m 2 measured on previously known embodiments of the marker of u s pat no 4 297 051 these measurements were made at the following conditions entrance angle 86 u00b0 observation angle 0 2 u00b0 rotation angle 0 u00b0 and presentation angle 0 u00b0 the inventive markers are installed in holes drilled in pavement typically by a core drill preferably it is a truck mounted air flushed drill driven by a power take off from the truck drilling time for one marker is about 20 seconds to one minute for a hole 45 mm deep the annulus between the base and the pavement is filled with a grout or sealant one useful sealant is an asphalt extended polyurethane the polyurethane comprises a two part system employing a pre polymer having an excess of isocyanate and a catalyzed dibutyl tin dilaureate hydroxyl terminated polybutadiene the two parts can be extruded through a static mixer from a two part cartridge gun one sealant found useful is lc 7241 detector loop sealant from minnesota mining and manufacturing company canada inc london ontario canada a solution of dibutyl tin dilaureate catalyst in toluene can be sprayed on the sealant after it has been poured into the annulus to hasten the formation of a protective surface skin.