Now that Mayor Jenny Durkan has decided to repair the cracked West Seattle Bridge rather than build new steel arches, the city moves to another high-tension challenge.

Can repair crews bring frustrated travelers back onto the bridge, and spare them countless hours in detours, significantly earlier than the Seattle Department of Transportation’s (SDOT) target of mid-2022?

The answer isn’t yet clear, but there are reasons to hope for a shorter closure.

Barbara Moffat, co-chair of the city’s panel of outside technical experts, called the mid-2022 timeline “realistically conservative,” and said rapid contracting methods can save time.

“Would I like to see it done quicker? Yes. Do I believe it’s possible? Yes,” she said. “But there are a lot of factors to consider.” Those include SDOT’s desire to observe thermal changes to the bridge this winter, before writing its repair-engineering plan.

The mayor announced Thursday that the city will embark on a $47 million repair program, as the surest way to return the Duwamish Waterway crossing to service soon.

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In doing so, she set aside her initial preference to replace three concrete bridge sections with twin steel arches and supports, at a cost of $390 million to $522 million. Durkan said that work might require five years to complete, including federal grant applications and environmental permits.

“This is a great day for Seattle,” said Port of Seattle Commissioner Peter Steinbrueck, who praised Durkan for moving faster than the usual Seattle process. He and Durkan both emphasized a need to unclog the area, after giant Terminal 5 on the west side of Duwamish Waterway opens next year.

Durkan also said she will collaborate with Sound Transit to design and build a new crossing by the early 2030s that serves light rail, personal vehicles, freight and bicycles.

“Ten, fifteen or twenty years from now we should be a city that is not reliant on vehicles and cars. We should be a city that relies on more climate-friendly options,” she said.

The high-rise bridge has been barricaded since March 23, when city structures director Matt Donahue saw quickly growing cracks, and called for an emergency closure.

Drivers are grumbling about what are typically 30-minute delays via the First Avenue South Bridge, especially their difficulty reaching hospitals and other services across town. Delays are expected to worsen assuming the coronavirus abates in 2021, and the Duwamish Valley gets flooded with traffic.

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Before the pandemic, an average 125,000 people a day drove or took buses on the high bridge. Though repair is the fastest solution, it’s still more than a year away, said former Mayor Greg Nickels, who co-chairs a community task force.

“That’s a long time, and it will seem even longer while you’re sitting in traffic,” he said.

Now that repair has won out, SDOT will face pressure to beat the estimate of an August 2022 reopening in last month’s cost-benefit analysis by engineering firm WSP.

“It’s clear to me that they are not truly trying to open this bridge as quickly as they can,” said Adam Ludwig. of the pro-repair West Seattle Bridge Now group.

If the city cares about quick restoration, he said, SDOT should trust the technical models it already has and keep its current emergency-stabilization team working full-speed through the winter.

Repairs would prolong the 36-year-old bridge’s life an estimated 15 to 40 years. The primary method is additional “post-tensioning,” in which strands of steel rope are strung through the hollow girders, then tightened at extreme pressure to support the concrete horizontally.

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SDOT’s conceptual repair schedule shows six months devoted to the engineering phase, followed by 13 months for crew mobilization, steel delivery and construction.

Moffat, a private-sector engineer who directed the 2011 Spokane Street Viaduct project nearby, mentioned three reasons for optimism, when asked at the mayor’s news conference Thursday.

First, the city can save time by bringing the construction contractors into the design team early, in hopes to make the job smoother, she said. It’s also possible, she said, to restore some traffic while repairs are still being completed.

“This is an eminently doable repair scenario,” said Moffat. “This is something that I believe very strongly — all of us are unanimous — this can be repaired and it is feasible to do so. Complex? Not necessarily.”

She noted that the original designers in 1980 created anchoring ducts for additional post-tensioning steel directly over the bridge columns, which SDOT can use to strengthen the 590-foot central mainspan. Using those built-in structures, Moffat said, “allows a standard methodology for repair.”

SDOT Director Sam Zimbabwe said the city will work as quickly as safety allows. Seattle officials have modeling data for how the bridge would react to new steel and carbon wrap, but say they need to see how the bridge behaves after crews cut open a stuck neoprene bearing this fall.

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“We have substantial risks before we are back to restoring traffic, and may not even know until we are back to the point of restoring live load on our repaired bridge, exactly how the bridge responds,” Zimbabwe told an online town hall Monday.

When the bridge is repaired, SDOT has pledged to conduct full inspections twice a year and to watchdog a full electronic network of monitoring devices.

Durkan said that a few weeks ago she favored the steel-arch replacement option. New spans could be built off-site, while the 1984 bridge is partly demolished, and delivered by barge. Ted Zoli, national bridge engineer for HNTB Corp, said the project could be completed by spring 2023.

But that version didn’t seem so rapid once Durkan studied local projects, such as the Elliott Bay Seawall, which needed a year or longer to win environmental permits. Briefings by members of Congress convinced her the federal government wouldn’t act on an infrastructure bill that would make new bridge money available until mid- to late next year, she said.

“I could not tell the public we would have that [steel bridge] operable and be able to restore mobility in three years,” Durkan told reporters. “I think it would be longer than that. Maybe five years.”

Durkan said her feedback from business and community advocates about which option to pick was about 50-50.

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The Martin Luther King Jr. Labor Council, and four labor members of the community task force, favored a new bridge, writing that it would disrupt traffic only once.

“There will never be less people, less freight, or less industry in Seattle. In short, there will never be a good time to rebuild this bridge, but we can say for certain it will get more difficult as time goes on,” they wrote.

Vigor Industrial, based on Harbor Island, described itself as “a potential fabrication partner” for the new steel arches, in a letter by Vice President Jill Mackie.

Lora Radford, executive director of the West Seattle Junction Association, thanked Durkan for a clear decision and reminded Seattle residents to support small businesses.

“Don’t forget about West Seattle. Pack a picnic, turn your GPS on, and come visit us.”