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The temporary Skagit River crossing on Interstate 5 is almost halfway assembled, leading state officials to believe they’re still on target to restore traffic lanes by mid-June.

The pace should quicken now that the National Transportation Safety Board (NTSB) has released the crash scene to the state Department of Transportation (DOT).

A tall truck load hit several crossbeams and caused the north span of the bridge to collapse May 23, dropping two vehicles into the water and causing minor injuries to three people.

People passing the site can watch the temporary span — actually two bridges cinched together — taking shape on the north riverbank, where scores of X-shaped steel rods form a lightweight structure. One of the two is nearly done, said Travis Phelps, DOT spokesman.

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Before the span can be installed, the remaining debris must be removed, primarily road decks, Phelps said. That might be finished by Friday.

Next comes a diver inspection to ensure the underwater bridge columns survived the crash intact.

The tops of the piers require repairs before new spans can be fastened. The pier caps sustained what officials call minor damage, when the falling bridge tore away from them.

This kind of structure is nicknamed a “Bailey bridge,” based on a design invented by Sir Donald Bailey in 1940 and used during World War II by Allied forces, who deployed 350 miles of them. Parts can be added, removed and interchanged like a Tinkertoy set.

The Bailey bridges are being prepared at 240 feet length, though the gap is only 160 feet. That way, they can be rolled out over the river on temporary supports, and land on the highway deck, beyond the first column. Parts will next be removed to shorten the bridge to fit.

“It’s almost like parallel parking a bridge,” Phelps said.

A permanent span, probably supported from beneath by long steel girders, will be installed in September.

Six contractors will submit proposals June 17, and a winner will receive notice to proceed June 19, Phelps said.

Initially traffic delays on the detour routes lasted 30 to 60 minutes, but DOT now says there is a few minutes’ delay on weekdays. Gov. Jay Inslee has allocated $150,000 in state aid toward a marketing campaign to benefit merchants near the bridge.

The NTSB plans to issue a preliminary report in late June about factors that contributed to the bridge collapse.

The agency also corrected an error made in its news conference of May 25, when it said Washington state doesn’t post height warnings on bridges unless the clearance is 14 feet, 4 inches or lower. Actually, the state posts bridges that are 15 feet, 3 inches or lower, using a three-inch fudge factor, so the sign on a 15-foot, 3-inch bridge would say 15’-0.” A legislative bill by Sen. Michael Baumgartner, R-Spokane, seeks to require posting of bridges with clearance 16 feet or less.

Includes material from The Associated Press and from David Blockley, “Bridges: The Science and Art of the World’s Most Inspiring Structures.” Mike Lindblom: 206-515-5631 or On Twitter @mikelindblom

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