MISSOULA — We don’t build major bridges in the Missoula Valley very often.

Of the current traffic corridors created by new crossings of the Clark Fork and Bitterroot rivers, just two are less than half a century old – Reserve Street, opened in 1979, and the Kona Ranch Bridge, 1985.

Both of those spans, as well as those others preceding it, generated public furors, much as the proposal to extend South Avenue across the Bitterroot River is doing now.

At issue is whether little Maclay Bridge downstream from the proposed new crossing is fit to handle the traffic loads to and from the Big Flat/Blue Mountain areas in decades to come.

Opponents of a new bridge decry its impacts in no uncertain terms.

“This new ($7.3) million bridge would be the longest ‘through’ city road in Missoula, shooting past two public schools and a few of the remaining ‘farm’ houses we have,” said Whitney Martin, whose children will be going to Target Range School and said she has “a mom’s perspective” for safety concerns.

A draft planning study initiated by Missoula County and prepared by Robert Peccia and Associates of Helena was released in late January. A comment period on the study ends Friday, after which the consultants, working with county, state and federal highway representatives, will make the necessary tweaks and present it to county commissioners by the end of the month.

Michele Landquist, who chairs the commission this year, has seen an uptick in comments as the deadline approaches.

Hers could be the first board of Missoula County commissioners in a generation to approve a new public route over a river in the valley, and the first in more than 80 years to create one over the Bitterroot River. Buckhouse Bridge, the only other one in the county, was reportedly moved downstream to its current location in the 1920s.

Landquist said Tuesday there’s a lot to evaluate, and while she’s been to the public meetings and heard most of the arguments, she‘s still “torn” as to whether the need, available funding and safety factors of a new bridge outweigh the consequences.

“I have some of the same concerns that citizens in that area have brought out, such as traffic calming and neighborhood characteristics,” Landquist said.

New bridges aren’t built often, she said, “but every time there’s some new goings-on at the river, we risk the unintended consequence of creating a recreation site, whether we intended to or not.”

She wonders if enough attention has been paid to impacts on residents west of Maclay Bridge on River Pines Road if the old bridge is closed.

Even though there’s a no-parking zone west of Maclay Bridge, people likely will continue to access the river there, perhaps in bigger numbers than before. That would add a burden on law enforcement charged with policing the area.

Another thing Landquist said to be considered: The road configuration at the west end of a new bridge, where River Pines Road would intersect.

“We’ll have to have some sort of traffic light or something for people that live in that short stretch, (because) making a left onto the new bridge will be a problem for them,” she said.

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While rare occurrences on Montana’s major rivers, new bridge construction across streams and rivers are not uncommon, pointed out Pat Saffel, fisheries manager for Montana Fish, Wildlife and Parks Region 2 in Missoula.

The Montana Department of Transportation lists nearly 150 bridges and culverts in Missoula County alone, although not all cross drainages.

Engineers are “very qualified” when it comes to bridging rivers, Saffel said.

“Basically, you just try to maintain the width of the river, so it passes water and doesn’t cause any constrictions, and you make sure the deck’s high enough so it doesn’t get hit by flood waters,” he said.

The fewer piers in the river the better, but the longer spans are going to require some, he said.

That’s one of the concerns at Maclay Bridge, where the abutments have altered the channel and created a dangerous whirlpool that has claimed many lives over the years. It’s one of the major arguments made by the Maclay Bridge Common Sense Coalition for building a new, modern bridge upstream and removing the current bridge.

Martin is urging county commissioners to postpone a final decision until more is known about the costs and consequences of a new South Avenue bridge.

She joins the ranks of several opponents who testified on Jan. 31 that the impacts of such a bridge would extend much farther than the river.

It would create a “straight shot” from Reserve Street to River Pines Road, past two schools with nearly 1,500 students between them, a major recreational complex at Fort Missoula, Community Medical Center and the Village Senior Living Center.

“There’s a huge percentage of commuters from the Bitterroot, from Lolo and Florence, and especially a lot of teenage drivers that attend Big Sky,” Martin said. “It would be a much shorter and more direct route for those people to take the new bridge, and so it would increase (by) a large percentage the high school students and other people who would be cruising through there from the Bitterroot.”