One of the most important highways in western Montana will be closed to through traffic for six weeks while contractors rebuild a key bridge west of Thompson Falls.
And with no available detours for commercial and recreational traffic, that means shutting down an important economic lifeline for the Lower Clark Fork.
The Highway 200 bridge just west of Trout Creek is one of the longest in western Montana, carrying traffic for 1,100 feet across the one narrow spot in the Noxon Reservoir. But like so many bridges, it's in serious need of attention.
"The substructure, or everything from below the deck, the piers and everything that holds that bridge is place, is still solid. But the deck is in really rough shape and needs to be replaced," Montana Department of Transportation District Administrator Bob Vosen said.
Some of that prep work has already been in place, with alternating traffic. But starting Monday, the entire bridge will be shut down. That means all the truck and RV traffic going between Idaho and Montana will have to detour via I-90, or U.S. Highway 2 through Libby and Kalispell.
The state would've liked to replace half of the deck at a time. But this bridge rests on just two long beams.
"The opportunity to do a half at a time becomes very challenging because we're asking half of a bridge to balance on one beam," Vosen said. "Which is not a really great situation to be in. I mean I'm not really eager to drive a vehicle over a beam that I hope I stay centered on, so the platform stays balanced if you will."
What makes this project so difficult is that it was originally built in the dry, before the reservoir was ever filled. Now those piers go down more than 200 feet into the reservoir.
"We spent a lot of time trying to figure out how to build this bridge," Vosen said. "Can we get a work bridge next to it, or a detour bridge? And it was just super cost prohibitive."
The project was planned long before the pandemic, but it's tough for businesses which were just starting to see tourism make a comeback. So the already planned shortcuts to keep the closure down to six weeks are even more important.
"The contractor's been busy pre-casting panels," Vosen said. "I think they've got to put together around 140 of these panels that are eight feet long and 28 feet wide. So it's going to be quite the project."
Local traffic might be able to squeeze by the old highway on the north side of the river. But there's no way it can handle through traffic. Boaters will still be able to use the reservoir, but will be channeled under the bridge to stay away from hazards.