Construction crews this month kicked off the final phase of a $133 million project to remake the northern convergence of Interstate 5 and Interstate 205.
The latest stage will bring the area its biggest change yet -- a 1,200-foot-long bridge carrying Northeast 139th Street over both freeways as part of a new interchange. But it will be at least two years before workers fully finish the new additions.
"This one's big and complex," said Leon Winger, a project engineer with the Washington State Department of Transportation. "It's nothing we haven't done before, but there are challenges."
The Salmon Creek Interchange Project, a joint effort between the state and Clark County, began construction in 2010. Earlier changes have already put a new C-Tran park and ride facility and roundabout off Northeast Tenney Road to the west of the freeways. Crews this year added a new lane on both directions of I-5. New sound walls reduce freeway noise in nearby neighborhoods.
The entire project aims to reduce congestion in a crowded and fast-growing Salmon Creek area. The new 139th Street bridge will add a new east-west route there, reducing some of the congestion that now plagues Northeast 134th Street. That's the centerpiece that ties the rest of the work together, said WSDOT spokeswoman Heidi Sause.
Drivers won't see any more major changes right away. Supports and foundations for the bridge won't start taking shape until later this fall, according to WSDOT.
Crews will eventually build the bridge in nine sections, Winger said. Construction will require short-term closures of both I-5 and I-205, but never both at the same time. At one point, the project could briefly close both directions of I-5 simultaneously.
Planners do their best to minimize traffic impacts when taking on a large project such as the Salmon Creek interchange, Winger said. But that doesn't mean compromising safety when working above two major freeways, he said.
"We're not going to set a girder over live traffic," Winger said.
The end result will allow drivers to access both directions of I-5 from 139th Street. Motorists on northbound I-5 will be able to exit at 139th Street. Southbound I-5 motorists, however, will not. Not yet, anyway.
"We've got plans for it," Winger said of the connection. "But they're unfunded plans."
The final stage of the project also means changes for I-205, which will be realigned and lowered to give vehicles enough clearance under 139th Street. That will mean multiple traffic shifts while crews use temporary lanes to get the freeway 5 or 6 feet lower, Winger said.
For now, Northeast 139th Street remains a dead-end near the new park and ride lot. The only freeway impacts this week are single-lane closures while workers put up new construction signs, according to WSDOT.
Drivers who frequent the area are used to seeing road work by now. They'll have wait a while longer before seeing the full benefits of the finished product, Sause said.
"Basically, this area's been under construction for a couple of years," she said. "It's going to look the same … until we get those big structures in place."