<p>An improved concrete block intended to serve as a roadway defining member. The block is in the shape of an elongate concrete body having an essentially triangular cross-sectional configuration with one bottom face and two preferably symmetrical side faces. Each side face is formed closest to the bottom face with a straight threshold portion sloping at a gradient of 1:5, which portion is connected to a second straight portion sloping at a gradient of 1:7 via en essentially circularly arcuate concave portion.</p>
