Along any State, Federal or major highway, or major street, no building or accessory building shall be located within fifty feet or closer than the setback established by the existing adjacent structures from the existing right of way of such highway or proposed right-of-way line on the City's major highway plan. Where there is no officially established public right of way for a road open to the public, all buildings shall be set back at least sixty feet from the centerline of the traveled roadway.