What’s Up with That? State had purpose for curved overpass

Now that the Northeast 139th Street overpass is completed and open, you can really notice how curved it is rather than straight. On Google Maps, the road on both sides of the interstates (I-5 and I-205) seems to be in perfect alignment. Why did the designers curve the overpass slightly to the south rather than just build it directly with no curve?

Seventeen years of planning, four years of construction and $133 million later, it’s finally done: a four-phase effort that also expanded I-5 between 139th Street and Northeast 179th Street, realigned I-205, improved local roads and built a new C-Tran Park & Ride lot.

But the centerpiece of the whole thing is that 139th Street bridge — one major solution to the hairball of congested traffic that long made the conjunction of 134th, Highway 99 and the two freeways everybody’s least favorite intersection. (Its reputation may be improving now.)

OK, but why build a curve into what could have been a straight roadway? Could it be a dreadful and expensive mistake?

Nope. Planners designed the bridge to bend to the south as it crosses the two freeways. Why? Because it leaves room for still-more improvements and freeway expansions, further out in the future — if you can get your mind around such a thing.

“We anticipate that we will eventually need to widen the two-lane sections of I-5 to accommodate future traffic needs,” Heidi Sause of the Washington State Department of Transportation 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.