One of the most heavily traveled bridges in northern Minnesota is tentatively scheduled to be replaced.

For 58 years the John A. Blatnik Bridge has spanned the St. Louis River, linking the Lake Superior port cities of Duluth and Superior, Wis. Along with serving daily commuters, the bridge has been a major artery for trucks hauling commercial loads along Interstate 535.

But corrosion and gradual deterioration have taken a toll, and the recurring maintenance has been time-consuming and a nuisance for motorists. As a result, the Minnesota Department of Transportation (MnDOT) is eyeing replacing the bridge beginning in 2028. The work could cost up to $460 million, to be split by Minnesota and Wisconsin.

MnDOT has committed to the project but is awaiting funding approval from the Wisconsin Legislature. In an e-mail Friday, Jessica Felix of Wisconsin DOT said that Gov. Tony Evers' budget "allows additional flexibility in funding preliminary design work for all major bridge projects. Blatnik Bridge would be considered a major bridge project."

Duane Hill, district engineer for MnDOT's Duluth office, said it's unlikely a new bridge could be built within the next five years because of the time involved in completing the environmental and design work. "It'll take a while," he said.

The Blatnik Bridge is the most heavily traveled bridge in Duluth-Superior, with 33,900 daily commuters, according to a study published by MnDOT in 2017.

Hill said long-standing deterioration has affected the bridge's carry capacity, however, making it clear that major work would be needed in the future. The severity of the deterioration didn't come to light until after the I-35W bridge in Minneapolis collapsed nearly 12 years ago, killing 13 people. Both bridges are steel-truss bridges.

The National Transportation Safety Board concluded that the I-35W bridge fell in large part because gusset plates, which hold together the bridge's steel beams, were too thin, making the bridge vulnerable to increasing traffic loads and weight.

"After 35W collapsed, we started to look at gusset plates and the carry capacity of them in truss bridges," Hill said. "We recognized that there were some concerns in the gusset plates on this bridge."

Consultants hired to inspect the Blatnik Bridge confirmed that a lack of preventive maintenance led to corrosion. Areas most affected were those regularly hit by splashes of salt, Hill said.

The deterioration of the gusset plates has led to annual inspections and regular maintenance to keep the 8,000-foot-long bridge safe. About six years ago, however, some began thinking about options to maintain the structure's long-term health, Hill said.

He said an analysis by an outside company made it clear that replacing the bridge was a better option than maintaining it.

"The most cost-effective decision would be to replace it sooner and it only interrupts the commuters one time" rather than have "regular interruptions every year" for inspections and preventive maintenance, he said.

Jenny Van Sickle, a Superior City Council member and board member with the Duluth-Superior Metropolitan Interstate Council, agreed. "When we don't have crews dedicated to consistent and exhausting maintenance, certainly that should make the commute more bearable," she said.

Annual inspections and maintenance on the bridge will continue through 2028.

David Mullen is a University of Minnesota student on assignment for the Star Tribune.