A wheel-load sensor cast into a mass of material for positioning in a depression in a pavement or the like. The sensor includes a piezo-electric pickup. The pickup encloses an inner electrode and is enclosed in at least one outer electrode. The inner electrode is a solid conductor and the outer electrode a hollow conductor. The pickup can be positioned in the pavement. Some sections (16) of the wall of the piezo-electric pickup (11) more or less parallel the surface of the road. These sections are accommodated subject to a prescribed pressure between the adjacent sections of the wall of the hollow conductor (13') that constitutes the outer electrode and the other sections (16') of the wall of the piezo-electric pickup in the hollow conductor and away from the rest of the walls.