When it is reasonably necessary in the interest of public safety, the department, in respect to the state highway system, a county, in respect to its county road system, or a municipality, in respect to its municipal street system, may authorize and direct the elimination of a grade crossing by construction of an underpass or overpass, provided that any such elimination shall be in accordance with this part and that no grade crossing on a county road system or municipal street system shall be eliminated upon order of the county or municipality until and unless the department shall approve the plans and specifications of the proposed construction.