A rerouting of trunklines in 1941 lead to the creation of a Business US 12 (Bus. US 12). M-96 ran concurrently with Bus. US 12 and M-37 was truncated to end at M-96. US 12 was rerouted between Galesburg and Kalamazoo in 1954, and M-96 was extended along the former US 12 routing to end in Kalamazoo. M-96 was rerouted in downtown Battle Creek to one-way streets in 1958, and Bus. US 12/M-96 was extended by the end of the decade when the I-94/US 12 freeway was completed in the area. Bus. US 12 was redesignated as BL I-94 in 1960 and M-96 was shortened to end at BL I-94/M-78 running on Capital Avenue. M-37 was reextended in 1961 in Battle Creek to a concurrent routing with M-96 in 1961.