A raised road marker (200) has a flat bottom surface (208) with an outer periphery. At least one cavity (214, 216) opens onto the bottom surface laterally inwardly of the periphery and extends upwardly into the marker body. A venting groove (218) extends along the bottom surface (208) from the cavity (214, 216) to the periphery to provide a vent for air trapped in the cavity (214, 216) when the marker is urged into a pool of adhesive to secure the marker to a roadway. The venting of air provides a stronger bond between the marker and adhesive. Markers having a rounded top surface (202) may be provided with a flat bottom portion (204) with abutment surfaces (210) to facilitate movement of a line of the markers in an automated system.