Abstract: Ballastless railroad lines are laid on prefabricated reinforced concrete slabs, which can eliminate the need for periodic maintenance of the ballast of traditional railroad lines, such maintenance being expensive and often difficult to carry out. Prefabricated, possibly prestressed, slabs are thereby positoned upon a steel reinforced concrete block having the functions of a foundation and connector for the prefabricated slabs with the interposition of a concrete-asphalt mortar layer between the slabs and block. The slabs are secured to the foundation block either by means of two half-cylinders, forming parts of the slab structure, or by shoulders formed by upturned sides of the foundation block (tub).