The cost of effecting any reconstruction, changes or alterations as contemplated in §§ 58-15-1910 and 58-15-1920, including the grade separation structure and its approaches for a distance of five hundred feet, if so much be necessary, measured from the center line in each direction along the highway, but not including the pavement or wearing surface for either the structure or its approaches, shall be borne sixty per cent by the Department of Transportation and forty per cent by the railroad company concerned and, in case of failure on the part of any such company to furnish its pro rata share of the necessary funds for paying the cost of any such reconstruction, changes or alterations, the Department of Transportation may, after thirty days’ notice, proceed with the work and collect from the railroad company concerned a proper pro rata share of the cost on the basis established by §§ 58-15-1910 to 58-15-1950.