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Ask an engineer: Milwaukee Trail tunnel “took a heck of a hole”

Posted: 7:05 AM, May 22, 2019
Updated: 2019-05-21 20:34:03-04
The Milwaukee Trail tunnel under Brooks Street stands 11 feet from floor to ceiling and stretches 106 feet long, making it a rarity in state transportation projects and unique to Missoula. (Martin Kidston/Missoula Current)

Martin Kidston – Missoula Current

It may not be the Eisenhower Tunnel carving through the Rockies at 11,000 feet, or the “99” diving under the streets in downtown Seattle.

But the new Milwaukee Trail tunnel in Missoula is an engineering marvel, at least on a Montana scale. Coupled with the new bridge over the Clark Fork River, some see the tunnel as the cherry on the Russell Street corridor project.

“It’s a big tunnel,” said Bob Vosen, a construction engineer with the Montana Department of Transportation. “It was a tremendous undertaking. It took a heck of a hole to get that tunnel in.”

Two years ago, Russell Street resembled a two-lane country road bisecting one of Missoula’s busiest corridors. The Milwaukee Trail crossed at grade, marked by little more than a few traffic signs.

But millions of dollars later and the street has grown to five lanes and is set to open later this year. The trail went underground during the process, crossing 15 feet below the surface of the road.

“It’s 106 feet long with a precast arch,” Vosen said. “The overall width is 20 feet wide and 11 feet from the asphalt surface to the ceiling. It’s wide enough that two cars could pass inside.”

The Russell Street project has been years in the making – dating back decades, in fact. When the first phase of the $29 million project finally came to bear, everyone wanted a piece of the pie.

And with so many interests at stake, Vosen said, designing the corridor may have been the hardest part.

“It took a lot of time and negotiations to find something in the design that met the needs of all the users of the corridor,” Vosen said. “It was a tight corridor with a lot of people interested in it. I think it’s going to be an incredible project when it’s complete.”

With the first phase of the Russell Street project entering its final stretch, attention has turned to the project’s second phase, which could be expedited if a funding agreement comes to fruition.

That phase would widen Russell to five lanes from Third Street south to Mount Avenue. It also involves the crossing of the Bitterroot Branch Trail, though it’s unlikely it will see a tunnel like the Milwaukee crossing.

Yet with the city’s focus on inward growth and boosting alternative transportation, the crossing must be addressed as the design progresses, Vosen said.

“There’s another trail crossing at the south end of Russell that will have to be dealt with, but I don’t think there’s a way to get under there,” he said. “It will have to be at grade or an overpass at the south end. That design hasn’t been completed yet.”

Aside from the Orange Street underpass, the Milwaukee Trail is Missoula’s longest tunnel. It’s also unique to the state, Vosen said. While pedestrian tunnels aren’t a rarity, a tunnel on the scale of Milwaukee is.

“We’ve got pedestrian paths in a lot of places, but I don’t know that we have anything to the scale of that one,” Vosen said. “This project is a great example of what can happen when a lot of people come together to figure out how to meet the needs of all the people of the corridor. It’s something other communities can look to.”