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Highway 18 wall's completion brings traffic relief and landslide protection

A containment wall built to protect westbound Highway 18 near Auburn from landslides was finished last week — 10 months after a January landslide shut the road down for days. The wall
A containment wall built to protect westbound Highway 18 near Auburn from landslides was finished last week — 10 months after a January landslide shut the road down for days. The wall's completion has provided some traffic relief on the steep roadway from the Auburn valley to Federal Way.
— image credit: Courtesy photo

A containment wall built to protect westbound Highway 18 near Auburn from landslides was finished last week — 10 months after a January landslide shut the road down for days.

Beside holding back debris that could cascade down the hillside flanking the highway this winter, the wall's completion has provided some traffic relief on the steep roadway from the Auburn valley to Federal Way. The Washington State Department of Transportation reopened the lane Oct. 28. The inside left lanes near the slide location were opened five days after the slide took place. But the truck lane remained closed, awaiting work on the containment wall.

"A big benefit of completing this containment wall is that we can reopen the truck-climbing lane again," project engineer Mark Sawyer said. "That's going to help traffic move better through this area. Plus, the wall will catch any slide debris so we can keep the road open for freight haulers."

As a main east/west connection, the highway is used by approximately 95,000 vehicles per day, WSDOT spokeswoman Bronlea Mishler said. The roadway, in both directions, is especially popular among freight haulers. Westbound Highway 18 starts near Snoqualmie, at the Interstate 90 junction, and runs through Maple Valley, Covington, Kent and Auburn before ending in Federal Way. Roughly 3,500 trucks travel the the stretch of highway from the Auburn valley to Interstate 5 per day, just east of the Enchanted Parkway and South 348th Street intersection, said Rick Perez, Federal Way senior traffic engineer.

The lane closure condensed westbound Highway 18 from three lanes to two. It forced semi-trailer trucks, other vehicles laboring to climb the grade and those cruising along at posted speeds to travel in the same lanes. The closure slowed traffic, but did not cause significant backups, Mishler said.

It was mostly an inconvenience to motorists, said Jim Tutton, Washington Trucking Associations staff vice president. Motorists got stuck behind slow-moving freight trucks and had fewer lanes to try to maneuver around the semis, he said. The truck lane is mostly a "good safety tool," Tutton said.

The containment wall is another safety tool. Westbound 18 from Auburn to Federal Way is carved into a hill; the area, since the 1950s, has been prone to landslides, Mishler said. WSDOT periodically checks the area to make sure the hillside is stable, she said. The January slide made it apparent that some form of permanent landslide relief was needed at that particular part of the hillside.

WSDOT went through various steps before deciding a wall was the best way to protect the roadway into the future. The slope was evaluated, relief options considered, a design for the containment wall drafted and the project put out to bid twice before construction began, Mishler said.

Crews were on site since August constructing the wall. The 10-foot high, 600-foot-long wood and steel wall was built to last a minimum of 20 years, Mishler said. The project was finished on budget and on time.

It cost $495,800 and was federally funded. The money was provided before construction began and came from emergency release funds. WSDOT was required to comply with federal standards in constructing the project due to the funding's nature.

Check it out:

Watch a video (below) of the construction work and hear comments from project engineer Mark Sawyer. To learn more, visit www.wsdot.wa.gov/projects/sr18/peasleycanyonslide.

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