View from highway Exit 336. I-75 continues South to Bay City.Note: This is the actual start of Highway #31. Also called the 'Michigan Circle Tour Route.'The Great Lakes Circle Tour is a designated, scenic road system connecting all of the Great Lakes and the St. Lawrence River. The Circle Tour is over 6,500 miles or 10,500 kilometers long. It encompasses individual lake Circle Tours including New York State's Seaway Trail system. The road route, marked by distinctive green and white signs, is usually the closest major road or highway to the water.