A new four-lane St. Croix River bridge — decades in the making, but taking only moments to cross — secured its place in Minnesota and Wisconsin history Wednesday, as thousands celebrated its long-awaited opening.

Local, state and federal leaders gave speeches and cut red ribbons at a morning ceremony to inaugurate the massive new bridge, the centerpiece of a two-state, $646 million transportation project joining Washington County with St. Croix County, Wis. In the evening, a crowd converged on downtown Stillwater to watch the permanent closing to car traffic of the 86-year-old Lift Bridge that the new bridge is replacing.

By midevening, traffic began streaming across the milelong new bridge. Motorists from both sides of the bridge moved forward like advancing armies behind escort vehicles with flashing lights. As they streamed across, they honked at hundreds of people watching them pass. Almost simultaneously, the Minnesota Department of Transportation shut down the Lift Bridge. Cheers and blaring horns were heard in both locations.

"It's the collective weight off our community's shoulders, the Christmas present we never got to open," said Stillwater Mayor Ted Kozlowski, standing among hundreds of people watching from the riverbanks Wednesday evening. "It's the golden age of Stillwater."

The new bridge, built in Oak Park Heights about 1.5 miles downstream from the old one, was dedicated under a steaming sun before hundreds of onlookers, many of whom watched from the hillsides on either side of the roadway.

"We've been waiting for it forever," said Bob Winter, a 44-year resident of Lake Elmo. "By the turnout today, a lot of people are excited and anxious to have it here."

Bus after bus rolled down the new highway leading onto the bridge, bringing residents from both states who wanted to witness a historic moment. What they saw was completion of the largest road and bridge project ever accomplished in Minnesota, as well as a significant project for Wisconsin, where a four-lane highway was built through the cornfields of St. Joseph Township to connect with the bridge.

Carolyn Craig, a retired nurse living in New Richmond, Wis., said she had been waiting for the new bridge since she moved to the area in 1960.

"It took a long time, but the bridge is beautiful," she said.

Bill Derrick, also from New Richmond, said the new bridge will benefit both sides of the river in unpredictable ways.

"It's certainly going to change. More growth," he said.

The exact timing of the bridge opening remained in doubt as late as Wednesday morning, when Gov. Mark Dayton, sitting at the dedication with Wisconsin Gov. Scott Walker, cleared up the mystery.

Oak Park Heights Mayor Mary McComber was at the podium when Dayton leaned from his chair and spoke to state Transportation Commissioner Charlie Zelle. "Charlie, is it still 8 p.m.?" Dayton asked.

McComber turned to the microphone. "Gov. Dayton has ruled it will be 8 p.m. tonight," she told the cheering crowd.

The Minnesota Department of Transportation had been coy about the timing of the bridge opening, concerned that a traffic jam might result. Although the crowd was huge, traffic flowed smoothly as the new bridge opened.

In addition to Dayton and Walker, elected officials cutting a series of ribbons for the new bridge included U.S. Reps. Ron Kind and Sean Duffy of Wisconsin and Tom Spaniol, town chairman of St. Joseph.

Minnesota and Wisconsin, Dayton said to laughter, "worked closely and cooperatively to make sure this bridge met in the middle."

Walker said the bridge will provide "an uninterrupted flow of commerce" and he applauded cooperation between the two states. "The St. Croix River may divide us, but this bridge unites us," he said.

"The one thing I failed to mention to Governor Walker is that tomorrow we begin work on a Minnesota toll booth," Dayton joked to the crowd. "Charges will be double for anyone with Green Bay Packers memorabilia."

U.S. Sen. Amy Klobuchar, who sponsored legislation seeking approval for construction of the bridge across the St. Croix, one of 208 federally protected waterways, sent a statement that read in part: "This stands as what can happen when we put politics aside."

Much of the political will for the new bridge came from Stillwater, a city fed up with interstate commuter traffic that has sliced for decades through its 1890s-era downtown and quiet neighborhoods.

The Lift Bridge, though retired to motor vehicles, will be spruced up and made part of a 5-mile pedestrian and cycling trail schedule to open in the spring of 2019.

Among the guests attending Wednesday's ribbon-cutting were Helen Josephson, 101, and her sister, Doris Erler. They were teenagers in 1931 when they and their father joined a crowd of about 15,000 people in Stillwater to witness the opening of the Lift Bridge.

Josephson, overcome in the heat Wednesday, was taken into the shade of an ambulance. Her son, Steve, said she often talked about how the Lift Bridge had changed Stillwater by replacing a dangerous older bridge on the river.

"People could go across without worry. Safely, that's one thing she remembers," her son said.

Stillwater's celebration Wednesday night observed the end of traffic crossing the Lift Bridge in much the same fashion as the 1931 celebration that greeted it — with speeches, noise, merriment and picnics.

Thousands of cars rolled slowly across the Lift Bridge as motorists took a commemorative drive.

The final drive would be done by owners of cars representing each decade of Lift Bridge operation. Dennis Murr, with a 1980s Corvette, was participating in that parade with his 12-year-old grandson, Kenyon Almer. "I think it's really cool to be one of the last kids to roll across in an automobile," Kenyon said.

At both bridges, most everyone talked about how the new bridge, first discussed in the 1950s, finally got built — and how they lived to see it happen.

Terry and Mimi Pederson came from Eau Claire, Wis., to witness the ceremony at the new bridge. He worked on the project years ago for the Wisconsin Department of Transportation and said he never doubted it would happen.

"I kept telling people I would be at the ribbon-cutting, or my wife would bring my ashes," Pederson said.

Kevin Giles • 651-925-5037