DULUTH — Seventeen St. Louis County bridges and box culverts will be replaced by 2024, after approval Tuesday of the largest road and bridge contract the county has ever put out for bid.

The St. Louis County Board unanimously approved a bundled bridge contract worth $23.9 million that in partnership with the Minnesota Department of Transportation will replace seven bridges and 14 box culverts, four of which are in Carlton County. It was awarded to Redstone Construction of Mora, Minn.

"It's a huge undertaking that will greatly improve the quality of our bridge system for all drivers, but in particular for heavier commercial vehicles," said board chair Paul McDonald in a news release. "So this is an economic development project as well as a transportation safety project."

Construction of 10 of the bridges and culverts is expected to begin this year, with another group of 11 in 2023. MnDOT is responsible for the Carlton County culverts.

Money comes from several sources, including the state Department of Transportation, the Local Bridge Replacement Program and the county transportation sales tax. The county is trying to secure additional federal and local bridge replacement money to reduce the amount of transportation sales tax money needed.

Combining the projects reduced the overall cost, county officials said.

St. Louis County maintains 600 bridges and culverts. The average age among those slated for replacement is 75 years. County communications manager Dana Kazel said most are in remote locations. A small bridge north of Mountain Drive that leads into the Spirit Mountain area is on the list for replacement, along with bridges north of Hoyt Lakes and east of Meadowlands over the Whiteface River.