M.17 a.k.a. M-17 is a 6.390-mile-long state trunkline highway in the U.S. state of Michigan, connecting the cities of Ypsilanti and Ann Arbor in Washtenaw County. It was once part of a highway that spanned the southern Lower Peninsula of Michigan before the creation of the U.S. Highway System in 1926. The designation once extended into downtown Detroit, but the eastern terminus was progressively scaled back in the late 1960s to the current location in Ypsilanti. The changes made to the highways in Washtenaw County spawned BUS M-17, a business loop for 11 years between 1945 and 1956.