The Department may temporarily close to traffic any portion of a State highway for the purpose of constructing, repairing or making improvements thereon. When a portion of a State highway with a route marking is so closed, the Department shall arrange with local authorities or otherwise to maintain efficient detours around the portion of the State highway which is closed and, except for an unanticipated emergency as determined by the Department, shall post notice of the detour locations on the Department’s website no later than 10 days before the detour becomes active. Such detour shall be plainly and conspicuously marked with signs by which traffic may be guided around that part of the highway so closed.