After one too many trucks have hit the 86th Street bridge over Interstate 35W in Bloomington, a stretch of the interstate will close this weekend and the battered bridge will come down.

Road crews will shut down parts of the interstate and reduce the number of lanes on other parts as they begin replacing the structure. Crews also will begin repairs on the 82nd Street bridge and make road improvements along the 8-mile stretch of interstate between Burnsville and Bloomington.

Northbound I-35W will be closed from Interstate 494 in Bloomington to Interstate 35E in Burnsville from 10 p.m. Friday to 5 a.m. Monday. The southbound lanes also will be closed from 90th Street to I-494 and reduced to a single lane from 90th Street to I-35E during that time. Crews will close the interstate ramps that lead to the closed section beginning at 8 p.m. Friday.

The weekend closure will allow crews to begin work on the two bridges as well as replace the top layer of I-35W at McAndrews Road in Burnsville. Crews also will do other maintenance work, including replacing guardrails, patching pavement and removing trees.

The current 86th Street bridge, which is 14 feet, 5 inches high, will be replaced with one that is 2 feet higher. The new bridge should be up by October.

The old steel-beam bridge has been hit multiple times by taller trucks, said Ed Lutgen, a bridge construction and maintenance engineer with the Minnesota Department of Transportation. Last year, load and lane restrictions on it were imposed as a safety precaution. But it was closed to all traffic after another truck traveling on I-35 hit it in April, he said.

The concrete-beam bridge at 82nd Street also was hit by the same truck and is reduced to a single lane in each direction until it's repaired. That work also is scheduled to be completed in October.

At least once a week a truck hits a bridge somewhere in the state, Lutgen said. Most bridges suffer little damage or pose a safety threat, he said.

The standard height for new bridges in "oversize" corridors like Interstate 35 is 16 feet, 6 inches, Lutgen said. But Interstate 35W was built decades earlier and the standard was shorter. Some of the bridges along that corridor, however, have been rebuilt or adjusted over the years to allow for higher clearance, he said.

Most semitrailer trucks meet the state's legal height limit of 13 feet, 6 inches, he said. Those that exceed it require a permit from the state and are directed to alternate routes.

Mary Lynn Smith • 612-673-4788