Michigan Kills Off Highways More Than Nearly Any Other State
It's the buildout of the Instate highways (like I-75, I-94 and I-96) that replaced many US highways (like US-31, US-23) that run along the same course.
How to deal with those parallel or overlapping highways varies greatly from state to state.
Widely stereotyping, states in the West have decommissioned these US highways while states in the East have kept them in place. Michigan is an outlier in this trend.
The road enthusiasts at AA Roads took at look at how states have delt with their 'legacy' highways.
The most aggressive state east of the Mississippi is Michigan, which no longer has US 16, US 27, and US 112 while truncating US 10.
US 16 was once Grand River Avenue that was replaced by I-96.
US 27 ran along I-69 for much of its run through Michigan from the Indiana state line to Lansing so the state cut the highway out and Indiana followed suit and dropped the highway north of Fort Wayne. A legacy of US 27 exists in the form of roadways called "Old 27" around Marshall and Lansing as well as M-27 which ends in Cheboygan.
US 112 was replaced by US 12 because US 12 was replaced by I-94.
US 10 currently runs from Ludington to Bay City at I-75. US 10 once ran south to Detroit. The legacy of US 10 in the Detroit area is seen with M-10, the Lodge Freeway.
There are even more of these displaced US highways in Michigan.
US 33 once ran from Niles to northern Berrien County. However, it overlapped a good deal of the way with US 31 so Michigan cut the highway out of its system and Indiana followed suit cutting US 33 back to end in Elkhart. The remaining Michigan portion of US 33 became M-63.
US 25 once ran along the Thumb and is today an M route of the same number, M-25.
So if you think there's much more to Michigan's highway system than you first imagined, you're correct.