Maclay Bridge is officially historic.
The National Park Service announced last week that the endangered, one-lane span in southwest Missoula was listed in the National Register of Historic Places on Dec. 20. It’s the first bridge over the Bitterroot River to make the list.
According to the nomination, other than limited periods of closure due to floods, some iteration of a Maclay Bridge has been in continuous use since the early 1890s. Missoula County has owned it since 1894.
The current bridge was built and installed in 1953, when an abandoned span over the Blackfoot River at Nine Mile Prairie replaced its predecessor, which had been washed away in the spring of 1948.
Brian Herbel and Janene Caywood of Rabbitbrush Archaeological Service in Missoula wrote the 30-page nomination, which was approved by the state historic preservation office in September and sent on to Washington, D.C.
They said the bridge connecting North Avenune in southwest Missoula with the rural Blue Mountain-Big Flat area “illustrates the creativity envisioned by the Missoula County Commissioners in the face of the fiscal constraints of the time.”
“It’s definitely worth saving and continuing to use into the future,” said Fred Stewart of the Maclay Bridge Alliance, which commissioned the nomination. “Engineers have said that can be done. It’s not going to fall into the river.”
Stewart’s group formed six years ago to contest a plan to replace Maclay with a modern two-lane bridge upstream that would extend South Avenue. An opposition group, the Maclay Bridge Common Sense Coalition, argues that the old bridge is classified as functionally obsolete and fracture critical by the Montana Department of Transportation (MDT) and its piers create an unsafe river channel.
In 2013, county commissioners Jean Curtiss, Bill Carey and Michele Landquist voted to accept a study team’s recommendation to replace the bridge with funding for the South Avenue extension through the federal Off-System Bridge Program. It carries a projected price tag of $13.1 million.
An environmental report was forwarded to MDT in December. Erik Dickson, project manager for Missoula County, said it should be back by late January and February.
The listing on the National Register won’t affect plans to remove Maclay Bridge, Dickson said.
“All it means is we have to consider the historical impact. It doesn’t mean we have to stop the project or the bridge has to remain in place,” he said.
But Stewart said the structure now becomes eligible for federal funding to be rehabilitated, a more cost-effective solution than tearing it down and building a new bridge.
In September the Maclay Bridge Alliance sponsored presentations by Dr. Jai B. Kim and his son Robert, a pair of engineers with expertise in saving historic bridges.
The Kims offered five options for rehabilitating Maclay and keeping it a passageway for vehicles. The one that seemed to curry the most favor would build arches to add “redundancy” to the main span, at a price of up to $1.26 million, and replace the “pony truss” bridge connected to the main span for another $800,000.
“We continue to come up with new information that we’re passing on to the county commissioners and to the public so they will consider rehabbing the bridge,” Stewart said.
Dickson said if the South Avenue Bridge project is approved without need of further environmental review, Maclay Bridge and its piers have to go.
“Even as a historic structure we do have permitting requirements,” he said. “If a new bridge is built upstream, there’s a pretty good chance permitting agencies aren’t going to allow that bridge to remain in place.”
County engineers say the existing bridge is too short for the channel it crosses, the west abutment having been built out over the years in order to stabilize it.
“We’ve also raised concerns of the number of piers in the channel (three), and how they accumulate material and debris and lead to further constricting of the channel,” Dickson said.
Maclay Bridge consists of three components — a Warren pony truss of unknown origin on the east end; the 180-foot Parker through truss moved from the Blackfoot River in 1953 (and likely constructed by the Federal Bureau of Public Roads in the 1920s or ‘30s), and two approach spans added in 1964.
“Although it is unusual to find pre-stressed concrete approach spans in association with steel truss bridges, the former have been components of the bridge since 1964,” the nomination reads.
“The combination of the different bridge types, steel truss and concrete, to form a single entity, fully displays the creative process required to construct an important link connecting the west and east sides of the Bitterroot River with minimal expenditure to the county.”