Old M-155 begins in front of the former state hospital on High Hillcrest Drive and runs north and northwesterly through a field and out of the property.

The trunkline follows Norton Road east over the South Branch of the Shiawassee River and then northeasterly past a residential subdivision.

Old M-155 then turns due east on Mason Road, running along the Marion–Howell township line before crossing into the city of Howell next to I-96.

After one-half mile (0.80 km), the trunkline terminates at the intersection with BL I-96 (Grand River Avenue) in downtown Howell.

[8] No section of Old M-155 is listed on the National Highway System,[9] a network of roads important to the country's economy, defense, and mobility.