A self-cleaning assembly employing a gap filler for a rail on the ground which guides or in which there runs rollers or wheels with lugs housed in a groove so as to lie flush with or protrude only slightly from the ground and which has a gap on the side of the rail corresponding to the passage of the lug. A filling substance is placed in the gap outside of the dynamic footprint of the lug and at least partially lines the gap, at least partially filling it. The filling material has properties of compressibility and is positioned in such a way that under all normal conditions of use or normal environmental conditions, the gap remains filled outside of the dynamic footprint of the lug.