If any building, structure or fence is erected or continued upon or over any highway, or if any fence, any part of which within 6 feet from the ground is barbed wire, is erected, maintained or continued adjoining or adjacent to any street or highway within the compact part of any town or within the limits of any village district or city, it shall be deemed a public nuisance. Cornices or other projections upon buildings, extending a reasonable distance into a highway, 12 feet or more above the surface of the highway, shall not be considered obstructions within the meaning of this section. Superstructures from one building to another, extending over a highway, not less than 16 feet above the surface of the highway, approved by the governing body of a municipality charged with the duty of inspection or supervision of buildings, shall not be considered obstructions within the meaning of this section.