New traffic circle in Salmon Creek aims to keep cars, and big rigs, moving

By Marissa Harshman, Columbian health reporter

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The North Salmon Creek Neighborhood is not only home to the people who reside there but now to the first roundabout in unincorporated Clark County.

Drivers encounter the roundabout instead of a T-intersection at Northeast 10th Avenue and Northeast 136th Street. Yield signs escort drivers into the intersection rather than a stop sign on 136th Street.

The intersection transformation is just one part of the $133 million Salmon Creek Interchange Project.

Northeast 10th Avenue serves as a connector between Northeast 134th Street, which leads to the current I-5 interchange, and Northeast 139th Street, which will lead to the new I-5 interchange.

Just west of the roundabout is the Fred Meyer store. To the north of the roundabout is the new C-Tran Park & Ride Lot.

The new roundabout has drawn questions and skepticism from people in the community, as was the case with other roundabouts in the county.

“It’s understandable that people aren’t that used to these traffic control devices and have questions about them,” said Jeff Mize, Clark County Public Works spokesman.

After construction began this spring, residents in the neighborhood raised concerns about the roundabout during a meeting with the county’s project manager. People were concerned the roundabout was too small and narrow, which could cause trouble for tractor-trailers, said Paul Scarpelli, president of the neighborhood association.

Most of those fears ease as residents become more familiar with the roundabout, he said.

However, for others, the concern about big rigs remains, particularly driving on the curb in order to maneuver the roundabout.

But, Mize said, the curb is there specifically for large trucks.

“People have a mistaken impression that trucks are not making it through the roundabout because they’re on the curb,” Mize said. “But that is precisely what that raised island is there for.”

That raised island in the middle of the roundabout is called a truck apron and acts as an extra lane for large vehicles, according to the Washington State Department of Transportation. The back wheels can ride up on the apron, allowing the truck to complete the turn. At the same time, the raised concrete discourages use by smaller vehicles, according to WSDOT.

The county settled on a roundabout after using a computer modeling system to monitor traffic volume, Mize said.

Increase expected

When the new Park & Ride opens, which is tentatively scheduled for Sept. 25, county officials expect traffic through the intersection to increase. The pre-existing T-intersection or a three-way stop would cause congestion in the parking lot during peak hours, Mize said.

A traffic signal at the intersection wouldn’t work either. A light at 10th Avenue and 136th Street would be too close to the existing light at 10th Avenue and Northeast Tenney Road. Cars backed up at one intersection would interfere with the other intersection, Mize said.

“(Roundabouts) effectively move traffic,” he said. “They also reduce collisions, particularly serious injury accidents and fatal accidents.”

According to the Insurance Institute for Highway Safety, roundabouts reduced injury crashes by 75 percent at intersections where stop signs or signals were previously used. In addition, roundabouts reduced fatal collisions by 90 percent, the institute said.

The new roundabout has been only open to vehicles heading northbound on 10th Avenue, which remained open to one-way traffic throughout construction. On Wednesday, the roundabout will open to both directions.

“We’re all putting up with the construction for now,” Scarpelli said. “But we all know there’s a big payoff for us in the very near future.”

Marissa Harshman: http://twitter.com/col_health; marissa.harshman@columbian.com; 360-735-4546.