The placement of the final girders over Interstate 205 next week will mark another milestone as the Salmon Creek Interchange Project approaches its homestretch.
Virtually the entire backbone of the bridge carrying Northeast 139th Street over I-205 and Interstate 5 will be complete. By the end of this year, the structure will be carrying traffic through the busy juncture, according to the Washington State Department of Transportation.
On Thursday, crews had hoisted into place six of the 10 girders that will support the easternmost section of the new bridge. Two more were set to go in tonight. The final two girders will be placed overnight Monday, said WSDOT assistant area engineer Devin Reck.
The work will mean one more complete closure of northbound I-205 at Northeast 134th Street, from 11 p.m. Monday to 4 a.m. Tuesday, Reck said.
Though earlier sections of the bridge were built high over vacant land, the east end of the structure requires work closer to the ground, and closer to freeway traffic. Workers had to realign I-205 to ensure that trucks would have enough room to fit under the new bridge.
"The critical thing is clearance — making sure you get the clearance right," Reck said
The bridge will provide 16 feet, 6 inches of headroom over I-205. Crews moved the freeway 40 feet to the east and lowered it 9 feet to make that happen.
"We've remeasured and measured and measured again just to make sure," Reck said.
The work is part of a $133 million effort to rebuild the crowded junction where I-205 and I-5 merge in Salmon Creek. Planners hope adding a new bridge at 139th Street will alleviate congestion in the area, including nearby 134th Street.
The Salmon Creek Interchange Project began construction nearly four years ago. It's scheduled to be done late this year.
"We're obviously very excited and waiting with bated breath for the ribbon-cutting," said WSDOT spokeswoman Abbi Russell.
During the next several months, workers will methodically build out the rest of the bridge and connecting ramps, Reck said. That's a repetitive process, he said — setting rebar, adding concrete, then doing the same on the next section. The eastern approach to the bridge will be supported by natural fill and expanded polystyrene blocks known as "geofoam."
The end of girder setting doesn't mean the end of traffic impacts. More freeway paving will still occur this year, requiring at least lane closures. And WSDOT hasn't ruled out additional complete closures of either freeway due to other overhead work, Russell said.
WSDOT has closed I-5 and I-205 at times during the project, but never both at the same time. Having the two freeways in close proximity at least gives drivers a relatively simple detour, Reck said.
"It's really an ideal location," he said. "It makes it a lot easier in terms of traffic impacts."