Interstate 675 constitutes an urban loop west from I-75 at Buena Vista Township to Downtown Saginaw. North from the city of Saginaw, I-675 separates Saginaw Township North and Carrollton Township to Tittabawassee Road. The freeway returns to Interstate 75 on the north side of Zilwaukee.
Designated in 1969, Interstate 675 was completed by 1971.1 The loop was initially considered as a reliever route for I-75 and the Zilwaukee Bridge, a bascule bridge spanning the Saginaw River. The Zilwaukee Bridge was a well known bottleneck along the drive between Detroit and northern Michigan, as the six-lane section of I-75 between Flint and Bay City narrowed to four lanes at the span. Openings along the old Zilwaukee Bridge often accommodated steel shipments from a General Motors plant in Saginaw.2
Construction got underway in 1979 to replace the bascule bridge along I-75 with a fixed, high-level span.3 During the same time steel shipments ceased from the General Motors plant.2 A major incident took place during work on the bridge when a 300 foot long section of the new deck tilted due to excessive construction loads. This pushed back completion of the Zilwaukee Bridge four years, which partially opened with two-way traffic on December 23, 1987. For a period of time, local drivers to displayed bumper stickers that read “I drove over the Zilwaukee Bridge AND LIVED!”. Locally referred to as the Z-Bridge, the new eight lane span was completed on September 19, 1988.2,3