A roadway marker comprises a solid body member having a lower generally planar surface configured to be adhered directly to a roadway surface. The marker is injection molded as a one-piece structure from a closed-cell foam thermoplastic material using a chemical blowing agent. The bottom surface of the body member may be formed with slight recesses or protrusions such that the entire bottom of the marker fills with adhesive when the marker is installed. Thus, maximum adhesive surface area is provided between the marker and the roadway surface. Further, the closed-cell foam construction creates a marker body which is strong, economical to mold and which does not shrink after molding.