M-39 is a 16-mile-long (26 km) north–south state trunkline highway in Metro Detroit area of the US state of Michigan that runs from Lincoln Park, on the south end, to Southfield on the north. The official southern terminus of M-39 is at the corner of Southfield Road and Lafayette Boulevard in Lincoln Park, one block southeast of the junction of Interstate 75 and two blocks northwest of M-85. From there the highway heads northward. The first 2.3 miles (3.7 km) of the highway follows Southfield Road, a divided highway in the Downriver area. It then transitions into the Southfield Freeway, which is a 13.7-mile-long (22.0 km) freeway that runs from I-94 in Allen Park north through Dearborn, and then the west side of Detroit, to Southfield. The northern terminus is at M-10 in Southfield.
M-39 bridge over the River Rouge in Dearborn
Michigan State Trunkline Highway System
The State Trunkline Highway System consists of all the state highways in Michigan, including those designated as Interstate, United States Numbered, or State Trunkline highways. In their abbreviated format, these classifications are applied to highway numbers with an I-, US, or M- prefix, respectively. The system is maintained by the Michigan Department of Transportation (MDOT) and comprises 9,669 miles (15,561 km) of trunklines in all 83 counties of the state on both the Upper and Lower peninsulas, which are linked by the Mackinac Bridge. Components of the system range in scale from 10-lane urban freeways with local-express lanes to two-lane rural undivided highways to a non-motorized highway on Mackinac Island where cars are forbidden. The longest highway is nearly 400 miles (640 km) long, while the shortest is about three-quarters of a mile. Some roads are unsigned highways, lacking signage to indicate their maintenance by MDOT; these may be remnants of highways that are still under state control whose designations were decommissioned or roadway segments left over from realignment projects.
Welcome sign along US 8
M-553 approaching Glass' Curve south of Marquette
M-121 in Jenison
Grand River Avenue, once a part of M-16 and later US 16, was originally an Indian trail converted as a plank road before becoming a state highway.