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The Lowry Hill Tunnel is congestion central in the Twin Cities on most days. A tie-up in the tube can bring traffic to a crawl and have far-reaching effects, choking things on Interstate 35W and Interstate 394, routes that feed lots of vehicles into the tunnel on the west end of downtown Minneapolis.

Now construction there is slated to begin and it won’t be pretty, with the potential to cripple traffic at all hours of the day for the next three months. Motorists will share one side of the Lowry Hill Tunnel with only two lanes 10 feet wide in each direction and a lower speed limit. Drivers on I-394 and I-35W will feel the pinch, too, as ramps to and from those arteries will shut down at times.

“This is a significant project and will be a challenge for drivers,” said Minnesota Department of Transportation spokesman David Aeikens. His warning also comes with a plea: “Give yourself plenty of time, plan alternate routes and don’t drive through neighborhoods.”

This week MnDOT gets to work on rehabilitating several bridges on I-94 near the Minneapolis Farmers Market and the International Market Square. Crews will actually lift the bridges off the pier caps and repair the concrete and pillars underneath. Think of it like when you jack up your car to do a tire repair, “only this will be done with much bigger equipment,” Aeikens explained.

MnDOT will use lots of scaffolding to hold bridges over Glenwood Avenue and Dunwoody Boulevard in place, but it is not strong enough to support the weight of traffic. So the bridges just north of the tunnel will be closed one at a time, and the only way to keep I-94 open while the work is done is to shift traffic to one side of the freeway and then the other. Crews also will replace broken and missing tile and repair the pavement in the tunnel, said project manager Tim Nelson.

Prep work begins Friday night when all eastbound lanes on I-94 will be closed between I-394 and I-35W as crews set up the barriers inside the tunnel that will separate eastbound from westbound traffic. The ramp from eastbound I-394 to eastbound I-94 also will be closed. Westbound lanes will stay open as usual.

At 5 a.m. Monday, the chaos begins. All traffic on I-94 between Hwy. 55 and 3rd Avenue S. will be shifted onto the eastbound lanes, including through the tunnel. The flyover ramp from northbound I-35W to westbound I-94 will shut down, so drivers heading into downtown are likely to feel the squeeze. Drivers who dare to brave I-94 through the tunnel won’t be able to go from westbound I-94 to westbound I-394. No getting off onto Hwy. 55 either.

After six weeks, traffic will switch from the eastbound lanes to the westbound lanes, and that configuration will last another six weeks.

If there is a shred of good news in all of this, it’s this: Large trucks will be prohibited from using the tunnel while the work is being done. Their detour is via Crosstown Hwy. 62 and Hwy. 100. Of course, those already crammed routes may pick up more than just trucks as motorists simply try to avoid downtown.

With more than 140,000 drivers passing through the tunnel each day, there probably is never a good time to do a project like this. But it starts on a weekend when thousands of out-of-towners will flock to town for the Twin Cities Pride Festival in Loring Park and the Back to the 50’s car extravaganza at the State Fairgrounds.

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.