The Washington State Department of Transportation (WSDOT) says it has no choice but to close the Montlake Bridge four weeks this summer, and replace worn-out steel decks.

Traffic will be blocked from Aug. 9 to Sept. 3, between Seafair and the Labor Day holiday weekend, WSDOT has announced.

Boat traffic will continue, and the walk-bike lanes will remain open. Work teams can move aside when ambulances need to cross toward UW Medical Center, but other vehicles will be blocked.

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The state has alerted construction teams to bid in early April for what’s expected to be a $4 million to $5 million contract. All 84 steel panels, about 20 years old, will be replaced during the August shutdown.

“It’s falling apart. Last calendar year on Montlake, crews had to go out nine different times and patch it up,” said WSDOT project engineer Hung Huynh. “If we don’t act, at some point things will get bad.”

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Then in the fall, there will be up to five weekend traffic closures, while crews renovate mechanical lifts. The bridge will be raised then, blocking walk-bike travel.

Drivers will be detoured to Interstate 5 and Highway 520, while transit buses take either those routes or the University Bridge. The work might create problems with cut-through traffic, such as on residential Boyer Avenue East.

WSDOT will avoid work-schedule conflicts with University of Washington football games, said spokesperson Bart Treece.

Traffic hassles are familiar in the area, where Highway 520 reconstruction has brought frequent weekend closures. Late this year, traffic will be shifted onto a Highway 520 lid under construction, while the main Montlake Boulevard is demolished and replaced.

An average 60,000 vehicles per day use the state-owned bridge, built in 1925. It originally included streetcars, and twin Gothic towers matched architecture of the university campus, according to HistoryLink.