The Associated Press
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The framework is in place, and workers are tightening bolts and welding sections on the temporary structure that's 24 feet wide and 160 feet long, spokesman Travis Phelps said.
Workers also are installing panels today that will be paved with asphalt to form the new bridge deck, he said.
And, they're finishing repairs and painting remaining sections of the bridge that were hit by a truck with an oversize load.
Some other work remains, such as divers' inspecting piers, so the department isn't saying yet exactly what day the bridge will reopen.
Traffic has been detoured through Mount Vernon and Burlington since May 23 when the oversize truck struck the north end of the bridge, causing one section to crumble.
The bridge carried 71,000 vehicles a day on a stretch of the interstate that connects trade and tourism between Seattle and Vancouver, B.C.
The new flow won't be completely back to normal, because the temporary section is narrower — traffic will be slowed from freeway speed of 60 mph.
The temporary span and a permanent replacement due this fall will cost nearly $18 million. The federal Transportation Department is paying for all but about $1 million of the work.
When it's finished, the state will have a repaired 58-year-old bridge that is still rated as functionally obsolete and fracture-critical, Phelps told The Daily Herald of Everett.
It's functionally obsolete because it was not designed to handle today's traffic volume and big trucks. Fracture critical means it is one more freak accident away from collapse.
A car and pickup truck went into the water when the bridge collapsed, and three people were rescued.
State Patrol Trooper Sean O'Connell was killed May 31 when his motorcycle collided with a truck while he was directing detoured traffic in Conway.