(1) To place upon the Commonwealth any duty to regulate traffic or police any such streets, but such duty shall be and remain the obligation of the cities;

(2) To place upon the department any authority to regulate traffic, parking or the general use by the traveling public of the streets, or sections thereof, taken over by the Commonwealth for maintenance or improvement under the provisions of any act of Assembly: Provided, however, That the department is hereby authorized to close to traffic all of the streets, or sections thereof, taken over as State highways, during such time as improvements are being made thereon, and in such case, the city shall establish and maintain a suitable detour in accordance with the provisions of section five hundred forty-eight of this act.¹