The historic, iconic and sometimes maddening Stillwater Lift Bridge closes forever to car traffic Wednesday, although good luck if you're angling to be the last driver on the 86-year-old bridge.

In perhaps the quirky span's last bit of mystery, the Minnesota Department of Transportation won't say exactly when it will close, only that it will be sometime overnight.

"We're not encouraging people to line up and do one last ride or anything like that," Minnesota Department of Transportation spokesperson Kent Barnard said. "That's why we're kind of keeping it under wraps when the actual closing will be, just letting people know that by Thursday morning, early morning, the Lift Bridge will be closed."

The bridge's cables are each made of 76 plastic coated steel strands surrounded by a steel tube. Evan Frost | MPR News

By then, the $650 million St. Croix Crossing bridge project will be open to traffic, connecting Minnesota Highway 36 directly to Wisconsin from Oak Park Heights. The shift will end years of St. Croix Valley commuter traffic through downtown Stillwater, traffic that over the years became a source of frustration for commuters and merchants as the region's population grew and the bridge became a choke point.

Many hope the closure of the Lift Bridge to cars and its eventual rebirth in June 2019 as a bicycle and pedestrian path will transform downtown Stillwater. Boat traffic will continue. Lift operators will still work the bridge to allow crafts to pass through.

At the Water Street Inn near the bridge, the bar connected to the hotel has been posting drink specials to celebrate the bridge closure.

"The main thing that we hear as a big complaint is the noise," hotel manager Jack Baglio said of his customers. "So, cutting that noise is going to boost business drastically."

Chris Kohtz, owner of The Wedge & Wheel restaurant in Stillwater Caroline Yang for MPR News

Chris Kohtz's cheese shop, the Wedge and Wheel, is a stone's throw from the bridge. He stepped out of the shop on a recent weekday to watch what has been a typical scene: traffic at a crawl, backed up in every direction from the stop light at the corner.

"At its worst, the traffic is on par with the worst of Minneapolis evening rush hour," Kohtz said. Car exhaust keeps him from opening shop windows or doors on a nice day and the noise is grating to customers, he added.

He also thinks many Stillwater residents stay away from their own downtown. He's confident all that is about to change.

"Many of them will say, the locals, we're not going to come down and deal with this," he said of the longtime traffic woes. "The net effect is going to be the crush of traffic, the noise, the car accidents, the kind of the risk to pedestrians. All of that is going to go away inside of a week."

That traffic — some 18,000 vehicles a day — is expected to shift over to St. Croix Crossing, where workers last week were still grinding down some temporary anchors on the bottom of the bridge as crews added finishing touches.

Eric Osten of Woodbury waits at the head of a line of traffic on Chestnut Street in Stillwater, Minn., as people wait for the Lift Bridge to be lowered for traffic to resume. Caroline Yang for MPR News

Building that span was a challenge, said Terry Zoller, the MnDOT construction manager who led the project.

"We really didn't know what the bottom of the river was," he said. "Turns out that the waterway is about 27 feet deep, but then you have about 85 feet of muck before you get to the bedrock. So, you're down about 125 feet."

Engineers designed an extradosed bridge, only one of which had been built in the U.S. at the time. It's a cross between a cable-stay bridge, like the Golden Gate bridge, and a box girder like the new Interstate 35W bridge in Minneapolis. The design was chosen to keeps the tower height below the tops of the St. Croix River bluffs. Planners hope that will prevent the bridge from becoming a visual focus in the river valley.

The new bridge has already helped fuel a small commercial boom along the east end of Highway 36. Planners are watching to see if that happens on the other side of the river, too. St. Croix County has been the fastest growing county in Wisconsin for decades, and about half the population commutes to work in the Twin Cities.

"As people shift traffic patterns, they'll shift where they decide to drive from. Maybe a little more north, instead of a little less south a little here, a little there, a little less commute so I can live a little further out," said Ellen Denzer, the county's community development director. "Those kinds of shifts we think we'll see."

Construction Manager Terry Zoller Evan Frost | MPR News

The bridge opening will mark the end of years of political and legal wrangling. The North Star chapter of the Sierra Club fought the project, saying it would irreversibly change the natural beauty of the St. Croix River valley.

Making it easier to drive over the river isn't a good investment, said Matthews Hollinshead, the group's conservation chair.

"We've just finished spending $650 million on a bridge to what some people might consider nowhere, given the density that is not there out in St. Croix County in Wisconsin," he said. "I can think of ways of using $650 million to serve a lot more people a lot closer to the center of the metro."

The bridge's low profile and muted colors are well thought out, says construction manager Terry Zoller. "The design itself is made to fit into the environment." Evan Frost | MPR News

While merchants won't miss cars backing up in Stillwater's downtown because of the Lift Bridge, you can still find some wistfulness over the bridge's closing

Rick Nelson and his wife drove up to the Lift Bridge in their Jeep Thursday night, just as the bell rang, the boom gate came down and, soon, the bridge began lifting up to allow boats through. Nelson cut the engine and enjoyed the wait.

"It's basically our last trip across," Nelson said. "Been living here for 30 years and you hate to see it go. It would be nice if they still operated it, but that's progress I guess."