Along any State, Federal or major highway, or major street, except in a "B-5" District, no building or accessory building shall be located within seventy-five feet from the existing center line of such highway or any proposed center line on the City's Thoroughfare Plan. Where there is no officially established public center line for a road open to the public, all buildings shall be set back at least seventy-five feet from the center line of the traveled roadway.