HYAK, WA (AP) A rockslide west of Snoqualmie Pass closed Interstate 90, Washington state’s principal east-west artery, and traffic backed up for miles along the principal alternate route, transportation officials said.

The freeway remained closed in both directions as workers struggled to open one lane of westbound traffic, and the state Transportation Department asked motorists to avoid unnecessary traffic through the Cascade Range. Approximately 28,000 motorists cross Snoqualmie Pass on an average weekday.

Traffic jammed U.S. 97 over Blewett Pass and U.S. 2 over Stevens Pass to the north.

“It’s like a summer Sunday,” Joy Dennis, a waitress at the Mountain View Diner on U.S. 2 in Gold Bar, told The Herald of Everett. “It’s bumper-to-bumper all the way.”

The immediate cause of the slide was unclear. Despite temperatures near freezing and approximately a 7-in. snowfall the previous night, “it doesn’t seem like it’s an unusual storm,” Julie Holcombe, a meteorologist with the National Weather Service, told The Seattle Times.

Unlike a slide in September, boulders as big as refrigerators hit the westbound lanes without causing any injuries shortly after 3:15 a.m. Sunday, east of the 3,022-ft. pass.

A later assessment showed the mountainside remained unstable, with “two to three times more material ready to go down on the road,” said Jamie Holter, a transportation spokeswoman.

Another agency spokesman, Michael P. Westbay, said experts estimated that as much material could come down as the hundreds of tons of rock that hit the westbound lanes 2 mi. west of the summit on Sept. 11, crushing a Volvo and killing three women on their way home from a concert at The Gorge Amphitheater near George.

Following the slide on Nov. 6, the freeway was closed to westbound traffic at Easton, about 70 mi. southeast of Seattle, and eastbound lanes at North Bend, approximately 30 mi. east-southeast of the city.

Later that day, officials moved the eastbound closure point to Exit 53 at the summit so it could be reached by people from the Puget Sound area, Westbay said.

Wilder Construction was hired to remove loose rock from the mountainside, clear the road and erect a protective fence on Nov. 7 in the eastbound lanes to make it safer for workers to survey the area.

“This area is on the list of at least 2,500 potential rock fall areas that the state has been monitoring,” Westbay said. It was scheduled to be reinforced using a method called rock bolting next spring.

Holter said additional plows and sanders would be working on the alternate routes, U.S. 97 and U.S. 2 to the north and U.S. 12 over White Pass to the south, but drivers were advised to avoid the passes if possible.

On Nov. 7, the State Patrol reported few problems despite heavier than normal traffic through White Pass, but backups of 5 and 6 mi. were reported between Blewett Pass and Leavenworth and westbound motorists faced 2.5 hours of creep-and-crawl traffic from Stevens Pass to Monroe, approximately 55 mi.

Worsening the congestion was traffic returning from Dad’s Weekend at Washington State University on the state’s eastern border.

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