M-72 (Michigan highway)
Michigan State Highway 72, or M-72, is a state highway in the U.S. state of Michigan, running from Lake Huron to Lake Michigan across the northern part of the Lower Peninsula. It became a coast to coast highway by 1947, and portions of the road have been relocated and improved since then. It is one of only three Michigan State Highways that cross the entire lower peninsula.
The western terminus is in Empire at M-22. The eastern terminus is in Harrisville at U.S. 23. The total length is 133.8 miles.
The first route designated as M-72 was in the 1920s and ran from just south of Lincoln east to Harrisville and then south along Lake Huron shore to Greenbush. In 1923, it was extended west to end southest of Barton City. Around 1927, the route was extended south to Oscoda and west through Luzerne to just east of Roscommon.
In 1936, the portion of M-72 along the shoreline between Oscoda and Harrisville became part of U.S. 23. In 1940, the route is extended westward through Grayling to just south of Kalkaska. A seven mile long discontinuous segment of highway some 45 miles west of Kalkaska near Empire is also designated as M-72. In 1946, the western segment is extended east into Traverse City. In 1947, the two segments are joined and the road now extends "shore to shore" from Lake Huron to Lake Michigan.
From 1947 onwards, the endpoints of the route have remained the same, although there have been realignments of the route in between.