Several additional months of inconvenience are ahead for the thousands of drivers who use County Road 81 each day to travel between north Minneapolis and Robbinsdale.

Last week, the Hennepin County Department of Transportation closed the southbound bridge over Wirth Parkway and Lowry Avenue and shifted traffic onto the northbound bridge with one travel lane in each direction.

That was not supposed to happen until spring, when the county plans to start rebuilding the two deteriorating spans that pass over Lowry Avenue and Wirth Parkway. But repeated weight limit violations raised safety concerns and prompted the swift action.

Five years ago, the county posted weight restrictions to keep heavy vehicles off the southbound span, which has corroded steel bars showing through on the underside where concrete has fallen away. Dump trucks over 24 tons and semitrailer trucks over 32 tons were banned.

Ongoing inspections revealed more deterioration. This fall the county instituted further restrictions, prohibiting any vehicle weighing more than 8 tons.

"At that limit, drivers commuting to work, stores, the [North Memorial Health] hospital would be unaffected," said county spokesman Colin Cox. "We still saw large vehicles going over it."

The repeated violations led the county to abruptly shut down the southbound bridge five months before bridge reconstruction is set to begin. Traffic is now restricted to one lane between N. 29th Avenue and N. Abbott Avenue.

"We like to leave things in their current configuration as long as possible as to not disrupt traffic, but if we have concerns, we won't wait," Cox said. With all the violations and next spring's construction project on the horizon, "we thought it would be best to remove all traffic off the bridge and shift people to the northbound bridge."

The county, in partnership with Robbinsdale and the Minneapolis Park and Recreation Board, will also rebuild a third span connecting westbound Lowry Avenue to northbound County Road 81.

County Road 81 is also known as West Broadway to the south of the bridges and Bottineau Boulevard to the north.

DWI enforcement continues

December has long been a dangerous month on the nation's roads.

This year, officials are highly concerned because of the alarming jump in motorists driving while high.

The National Highway Traffic Safety Administration (NHTSA) found the number of motorists involved in crashes that resulted in a serious injury or death and tested positive for opioids nearly doubled after mid-March with the onset of COVID-19, as compared with the previous six months. Marijuana use was up by about 50%.

"Drivers engaged in more risky behavior," said NHTSA Deputy Administrator James Owens. "That is why we are stepping up efforts to keep impaired drivers off the roads."

NHTSA is spending $9.5 million on an ad campaign to warn motorists of the dangers of impaired driving and that law enforcement will be out looking for them during the holidays.

In Minnesota, police will work overtime through Dec. 31 to encourage sober driving.

"We are happy to be part of this nationwide crackdown to go after those who make the horrible decision to get behind the wheel when impaired," said Col. Matt Langer, chief of the Minnesota State Patrol.

Follow news about traffic and commuting at The Drive on startribune.com. Got traffic or transportation questions, or story ideas? E-mail drive@startribune.com, tweet @stribdrive or call Tim Harlow at 612-673-7768.