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The early development stages for replacing decades-old timber bridges between Bozeman and Wilsall are underway.

The Montana Department of Transportation has launched the MT 86 Structures project to replace the aging pieces of infrastructure. The asphalt-topped timber bridges, which cross Cache, Flathead and Carrol creeks, dot the route along state Highway 86. Plans for the project may not be ready until 2023.

“We’re planning for the future to get them replaced before it becomes a must,” said J.R. Taylor, a Montana consultant project engineer working on the MT 86 Structures project.

Roughly 400 cars drive over the three bridges each day, Taylor said. Much of the traffic comes from Bozeman, with drivers cruising along the scenic highway, which passes the Bridger Bowl Ski Area.

The project is spurred by leaps in growth in Bozeman and Gallatin County, and how that growth will affect traffic over the bridges along Highway 86. Census data released earlier this month showed that Gallatin County jumped to the second-most populous county in the state, edging out Missoula County by roughly 1,000 people.

Funding for the project has yet to be secured. Replacing the timber bridges is not on the Montana Department of Transportation’s tentative five-year construction plan, but the project could find a way onto the list because of a yearly review of the five-year plan that evaluates available funding for projects around the state.

A rough estimate for the cost of construction in replacing the three bridges could come out to around $2 million, Taylor said. However, that price tag could change depending upon cost of materials and what structures are chosen to replace the bridges.

Federal funds from the $1.2 trillion infrastructure package that passed through the Senate earlier this month could help speed the process, Taylor said. Typically, the Montana Department of Transportation gets funding from the state’s gas tax and federal dollars.

Fuel taxes in Montana did not increase between 1994 and 2016. The per-gallon tax on gas and diesel stayed at $0.27 and $0.2775, respectively, for more than two decades. In 2017, the state Legislature adopted a tax increase for fuel sales for the next six years in order to help pay for road and bridge maintenance and repair.

The money collected from these taxes goes into a Bridge and Road Safety Accountability Restricted Account. The Montana Department of Transportation receives 35% of the tax money, with the rest going to local governments.

Taxes on fuel in Montana increased to $0.325 per gallon of gas and $0.295 per gallon of diesel this July.

The timber bridges in question were built around the time of President Franklin D. Roosevelt’s New Deal. The New Deal poured money into public works projects around the country during the Great Depression.

Around 3,000 miles of new roads and roughly 1,200 timber bridges were built in Montana from that federal money. Of those timber bridges from the late 1930s, around 440 are still in service on Montana Department of Transportation roads and highways.

Taylor said that the Montana Department of Transportation hopes to get between 75 and 100 years of use out of new infrastructure from projects like MT 86 Structures. Replacements like concrete box culverts or prefabricated bridge structures are all on the table. Taylor has the advantage of time on his side to figure out what replacements would be the best fit.

“At this time we haven’t ruled anything out because we want to do our due diligence in our assessment and make sure we’re selecting the right structures,” Taylor said. “We want to select something that is going to be pertinent for a long time.”

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Alex Miller is the county and state government reporter and can be reached at amiller@dailychronicle.com or by phone at 406-582-2648.

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