Madison Street Bridge has low rating
A jogger passes beneath the Madison Street Bridge earlier this week on a run along the Clark Fork River. According to a Montana Department of Transportation report, the bridge has the lowest sufficiency rating among the major bridges in Missoula. Photo by KURT WILSON/Missoulian Kurt Wilson

The Russell Street Bridge is in line to be replaced, but on paper, it's not the worst bridge in Missoula.

The Montana Department of Transportation inspects bridges, and the Madison Street Bridge and Maclay Bridge get lower "sufficiency" scores than Russell. But the structures are safe, MDT bridge engineer Kent Barnes said Thursday.

When inspectors rank a bridge, they give it a "health index" score. They also score it for "sufficiency," which takes into account other factors, such as traffic and alignment.

The Russell Street Bridge, for example, earned a score of 88 out of 100 on the "health index," but because it isn't accommodating all the traffic coming its way, it scored just 55 points in "sufficiency" in a report last year.

The gap in the scores for Maclay is even more stark. That single-lane bridge over the Bitterroot River seems solid as a Clydesdale, with a "health index" rating of 96.49. But in its most recent report dated October 2009, the bridge gets just 43.2 points for "sufficiency."

County public works director Greg Robertson said the bridge was nominated about a decade ago to be replaced through the state's bridge replacement program. Now, its sufficiency rating is around 32, and it has risen to the top four for funding.

"The state, based on their current revenue stream, is telling me if construction is going to happen, it's probably seven to 10 years out," Robertson said.

He said the trusses are fine, but the bridge is limited in the weight it can carry and is deemed "functionally obsolete." It accommodates "basically, one school bus at a time" and is off limits for emergency responders like fire trucks.

The county is at the very beginning of a public process to see what the community wants to do. One idea that's been in the mix is to build a separate bridge off South Avenue to carry heavy traffic and use the Maclay Bridge for walkers and bikers.

The bridge is "functionally obsolete and eligible for replacement," but taking motor vehicle off the bridge would bump up its sufficiency rating, Barnes said: "As a pedestrian structure with some controls on that, it would be adequate."

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News that the Madison Street Bridge didn't get high marks surprised city public works director Steve King.

"It's one of our better bridges," King said. "Of course, the Madison Street ‘underbridge' was relatively recently constructed, and that was done with full cooperation with MDT, so obviously it had the capacity to accommodate the underbridge."

Barnes agreed and praised the underbridge: "That was a nice project. I was happy to see that."

The Madison bridge scored 88.12 on the health index and 52.8 on the sufficiency scale, and Barnes said while the bridge is safe, it will be due for maintenance in the "not too distant future."

In bridge years, that's five to 10 years, he said. The concrete on the deck is cracking and spalling - the equivalent of potholes breaking out in asphalt - and will slowly deteriorate over time, he said. And spalling isn't easy to patch. A reinforced concrete abutment has a spall with exposed rebar, contributing to the lower score.

"It's going to need some work in the not too distant future," Barnes said.

But the structure is "very adequate" for Missoula, said public works director King. On the other hand, he said the bridge that's been a concern to the city is the railroad bridge over Orange Street. The city maintains the pavement and Montana Rail Link inspects that bridge.

MRL spokeswoman Lynda Frost said the bridge is inspected twice a year as part of a regular schedule, plus on an as-needed basis. She said MRL doesn't have inspection reports, but it tends to any necessary fixes immediately.

"If there is anything of concern, it's repaired right away," Frost said.

She said bridges are a high priority for the company because a problem with a bridge can shut down the entire system.

Chunks of concrete are falling off parts of the bridge and in some places rebar is exposed. Frost said if any damage needs to be repaired, MRL does so.

"Typically if there is something that occurs, say for example a piece of concrete that falls, we have somebody right there to make sure that that's not going to evolve into a bigger problem," she said.

The nature of repairs made wasn't available, "We don't have maintenance records available to the public."

The inspection reports from MDT on several other bridges are posted on MissoulaRedTape.com. Included (in shaded box) are the most recent scores out of 100. Barnes has said the scoring system uses the entire scale, so a score of 50, for instance, can't be equated to a failure as it can on a school report card.

Reporter Keila Szpaller can be reached at @KeilaSzpaller, 523-5262, keila.szpaller@missoulian.com or on MissoulaRedTape.com.

 

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