Along its route in the state, I-75 utilizes three of Michigan's monumental bridges. The first of them is the Zilwaukee Bridge near Saginaw. The original bridge across the Saginaw River at Zilwaukee was built in 1960 as a bascule bridge to allow shipping traffic to use the river. Opening the drawbridge would back traffic up on I-75/US 10/US 23 for upwards of four hours on holiday weekends. Approved in 1974, construction on the replacement bridge started in October 1979. A major construction accident in August 1982 delayed completion of the new Zilwaukee Bridge; a bridge pier partially collapsed when contractors overloaded a section under construction. The affected deck segment tilted to rest higher on one end and lower on the other. The structure was originally supposed to cost $76.8 million with a 1983 completion date; in the end it cost $131.3 million (equivalent to $ in ) when the southbound span finally opened on September 19, 1988. The structure is the largest concrete segmental bridge in the United States.