[With regard to any county which is exempt from the provisions of Section 19-2-3, this section shall read as follows:]
Whenever in the discretion of the board of supervisors of any county it seems proper so to do, the board may, by order on its minutes, authorize the commission of any road district within the county, or the engineer of such commission, to forbid the use of any hard surfaced road, or portion thereof, when under construction or repair. The Highway Commission or its engineer, when so authorized by the board of supervisors, may close said road or any portion thereof to travel by an obstruction placed thereon in such manner as to indicate its closing, or by a sign marked “closed by order of the Highway Commission.”