(a) The commissioners court of a county shall establish detour roads for the convenience of the public when a county road that is not part of the state highway system must be closed to traffic for road construction. When a county detour road is in use, the county has the same authority over the road as over an established public road.
(b) The commissioners court shall:
(1) post all signs necessary for the convenience and guidance of the public at each end of a county detour road; and
(2) maintain a county detour road so that it is reasonably adequate for normal traffic requirements.