 The first sections of freeway for I-75 were opened in 1957, beginning with the southern section near the Ohio state line opened in October 1957.The Mackinac Bridge was opened to traffic on November 1, 1957; a new section of freeway and an interchange connected US 2 to the bridge on the northern end, and to US 27 and US 31 on the southern end.The MSHD formally proposed the I-75 number in 1958.