What’s Up With That? A curved bridge at Salmon Creek interchange?



I drive by the freeway construction in Salmon Creek often, and it looks like the bridge supports going up now don’t line up with Northeast 139th Street, where they’re supposed to connect. Is that new bridge going to bend somehow to get over the freeway? There’s no way they could have put them up in the wrong spot, right?

— Mark in Salmon Creek

As you know, Mark, construction crews are building a new bridge that will carry 139th Street up and over the junction where Interstate 5 and Interstate 205 converge. That work is part of the $133 million Salmon Creek Interchange Project.

But don’t worry, you’re not hallucinating. Your observation is correct — planners designed the bridge to bend to the south as it crosses the two freeways. It will still connect with 139th Street on each side, but not with a straight shot.

Here’s why: building for the future, according to Heidi Sause, a spokeswoman with the Washington State Department of Transportation.

“We anticipate that we will eventually need to widen the two-lane sections of I-5 to accommodate future traffic needs,” Sause said in an email. “By building the Northeast 139th Street Bridge with a curve, we leave space for cranes and other large construction equipment to access this section of I-5 in the future.”

Plus, the curved bridge design helped minimize wetland impacts and reduce right of way costs, Sause said.

Construction work will become a lot more noticeable to drivers as the 139th Street bridge takes shape later this year. Crews will have to close I-5 and I-205 at times, but never both at the same time, according to WSDOT.

When it’s finished, the new bridge will be 1,300 feet long, adding another east-west crossing to an often-clogged interchange.

The entire project is expected to wrap up in 2014.

— Eric Florip

Got a question about your neighborhood? We’ll get it answered. Send “What’s Up With That?” questions to neighbors@columbian.com.