The John A. Blatnik Bridge is the bridge that carries Interstate 535 (I-535) and U.S. Highway 53 (US 53) over the Saint Louis Bay, a tributary of Lake Superior, between Duluth, Minnesota, and Superior, Wisconsin. The bridge is 7,975 feet (2,431 m) long and rises up nearly 120 feet (37 m) above the water to accommodate the seaway shipping channel. It was dedicated on December 2, 1961, but was renamed for Congressman John Blatnik on September 24, 1971, to commemorate Blatnik's role in making the bridge a reality. The Blatnik Bridge replaced a swinging toll bridge around the same location that carried both automobile and rail traffic.
The bridge was widened and the substructure was strengthened between 1992 and 1993 to accommodate hard shoulders. The Blatnik Bridge was reduced to two lanes temporarily in 2008, after it was discovered in a bridge inspection that the 1990s upgrades to the Blatnik Bridge had added weight beyond the load limit for gusset plates in eight different locations. This was similar to the gusset plates that caused the I-35W Bridge in Minneapolis to collapse on August 1, 2007. The Blatnik Bridge was reduced to two lanes temporarily until the gusset plates could be strengthened.
In November 2011, both the Minnesota and Wisconsin departments of transportation installed new signs to remind drivers that trucks over 40 short tons (36 t) gross vehicle weight cannot use the Blatnik Bridge; these vehicles will be rerouted to the nearby Bong Bridge. According to the press release, permitted, overweight vehicles have been restricted from using the Blatnik Bridge since early 2008 when inspections showed that corrosion and time were starting to affect the structure. Transportation officials say that the bridge is aging and restriction of overweight vehicles will help to extend the life of the bridge. Drivers who disregard the posted weight limits will be ticketed.