sentences:  The last major interchange occurs at 4 Mile Road just south of Grayling where US 127 northbound ends with traffic merging onto northbound I-75 and the southbound starts taking drivers southward through the center of the state.At Mackinaw City, I-75 intersects the northern ends of US 31 and US 23 before crossing the Mackinac Bridge to reach the Upper Peninsula (UP).I-75 is the only Interstate located in the UP, and it continues until the Canadian border in Sault Ste.