 A rare type of special route, known as the Emergency Detour route, is signed with an auxiliary "Emergency" banner that is colored orange, indicating a temporary traffic control sign.The purpose of these routes is to offer an alternative in the event that the parent route is impassable, due to either a traffic jams, traffic collision, or road closure (for a variety of reasons).Emergency U.S. Route 31, which offers an alternative crossing of the Grand River in the event that the bascule bridge in Grand Haven, Michigan is unavailable for motorists, is one such route.