HYAK — After 64 years protecting Washington drivers from avalanches, the Snoqualmie Pass snowshed’s days are numbered.

Demolition begins Sunday to make room for the next phase of the Interstate 90 improvement project, a massive, yearslong endeavour that involves widening lanes, straightening curves and building bridges that will allow drivers to cruise over the path of future avalanches.

The snowshed, which dates to the Truman administration, will take just three or four days to pull, using equipment that crunches concrete into rubble, said Jason Streuli, the project manager for Atkinson Construction, contractor on the project.

It’ll cost about $500,000 to pull down the structure, which was built for just $342,000. It’s just a small piece of the $551 million improvement project scheduled for completion in 2018.

During a media tour Thursday, state Department of Transportation staffers snapped selfies with the snowshed and explained that the construction date of 1950 stamped in the concrete above the tunnel entrance will be saved for eventual display at the DOT office in Union Gap.

Removal of the snowshed might be the most sentimental part of the construction efforts, but it’s just a small part of the work planned for the next two weeks. Traffic will be reduced to one lane in each direction until April 26 so crews can set up the detours needed for the summer construction season.

The DOT warns that drivers could expect delays of up to two hours during peak travel times and recommends that drivers plan to travel early in the morning or late at night, or take alternate routes to avoid delays.

“It’s like (ripping off a) Band-Aid; we’ve just got to get it over with,” said Brian White, DOT’s assistant regional administrator for I-90 construction. “By doing this, we get enough room to have four lanes open during summer construction.”

Last summer, the DOT finished building a new lane in each direction for the 3-mile stretch along the western half of Lake Keechelus. This summer, they’ll begin work to add the new lanes to a very narrow, curving stretch along the middle of the lake.

“The biggest challenge is where to put the traffic while we do the work,” explained Will Smith, project manager for DOT. “That, and we only get six months of good weather to do the work.”

That’s why the detours under construction this month will be so critical. For the summer, traffic will be shifted south into four lanes — two each way — closer to the lake so that crews can blast away enough of the hillside to expand the highway.

They’ll remove 270,000 cubic yards of rock from the north side of the highway this summer, Smith said. That’s more than 500,000 tons. Crews will use it to fill in along the lake’s edge in some areas to construct a new eastbound lane and straighten curves.

Once the hillside is blasted back sufficiently, traffic will be routed into four temporary lanes along the north side of the highway so work can begin on construction of avalanche bridges across the area where the snowshed stands.

The bridges, about twice as long as the snowshed, will carry drivers above the path of avalanches as they head toward the lake. A similar bridge was constructed in the westbound lanes just west of the Snoqualmie summit in the early 1980s.

The new bridges will be built above another very active slope for avalanches, explained John Stimberis, an avalanche specialist for DOT.

“Multiple (avalanche) starting zones all feed into one very consistent path, which empties right onto the highway,” he said. “On a busy winter, that path can consume a lot of my time.”

Stimberis said that once the $78 million bridges are built, road crews won’t need to do avalanche control work — triggering small avalanches to prevent big ones — which can cause significant delays for motorists.

But, for the next few years while the bridges are under construction and the protective snowshed is gone, Stimberis said avalanche closures might last a little longer because crews will have to clean more snow off the roadway after control work before traffic can resume.

Streuli, the construction manager, estimated that about 100 people will be working on the project this summer, around the clock.

Snoqualmie is the state’s busiest mountain pass. On average, about 28,000 vehicles travel I-90 over Snoqualmie Pass every day.

For those drivers, these next two weeks should be the worst, DOT spokeswoman Meagan McFadden said.

Two eastbound lanes will be open on Fridays and two westbound on Sundays to accommodate peak traffic, but otherwise only a single lane will be open in each direction.

She recommends planning ahead by checking the DOT’s updates and traffic volume charts on its website, www.wsdot.wa.gov/projects/i90/whatshappening.

By getting the work done now, she added, the detours will be ready by the time more people want to hit the road this summer.