It was replaced by Interstate 94 in 1952. It was an old highway that ran through the middle of the major towns and cities of Michigan between Detroit and Chicago. In most cases the road is still there and either named Michigan Avenue or Old U.S. 12. You can still drive the highway from Belle Isle in Detroit all the way to The Miracle Mile in Chicago. There are only a few places were you have to navigate around the new Interstate. The major break in Old U.S. 12 is in the middle of Michigan half way between the village of Parma and the city of Albion. It's at this point that I-94 cuts south a bit and bisects the old highway, forcing a motorist to navigate north on smaller roads.
The highway is an important historic road like Route 66.
Cities on Old U.S. 12: Detroit, Michigan, Dearborn, Michigan, Ypsilanti, Ann Arbor, Michigan, Chelsea, Michigan, Grass Lake, Michigan, Jackson, Michigan, Parma, Michigan, Albion, Michigan, Marshall, Michigan, Battle Creek, Michigan, Kalamazoo, Michigan, St. Joeseph, Michigan, Niles, Michigan, Gary, Indiana, Chicago, Illinois