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If you need to get from the Eastside to Seattle any time between Friday evening and the following Friday morning, heed this warning.

Be prepared for big traffic tie-ups.

That’s what state transportation officials are begging drivers to do before several westbound lanes are closed to replace two huge expansion joints on the Interstate 90 bridge between Bellevue and Mercer Island.

All westbound I-90 traffic will be reduced to one lane at a short choke point near Bellevue Way Southeast, creating backups that could stretch more than 10 miles, officials say.

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Onramps from Bellevue Way Southeast and Interstate 405 will funnel drivers into three westbound lanes that will remain open west of the choke point and onto the bridge.

Crews will shut down lanes by 9:30 p.m. Friday. State transportation officials hope they will reopen all lanes by 5 a.m. ­July 25.

In addition to recommending alternate routes, such as the Highway 520 floating bridge or Interstate 405 to Interstate 5, the state Department of Transportation (WSDOT) is asking people to do anything they can to keep more wheels off the road. Although the closures are on I-90, westbound traffic backups could increase on 520 and I-405.

WSDOT spokesman Travis Phelps said the time to set up a week of telecommuting or carpooling with co-workers is now — before getting stuck in traffic. About 85,000 vehicles travel westbound on the I-90 bridge on an average day, he said.

“What can you do to keep some wheels off the road? We want people to be thinking about that this week,” Phelps said. “Don’t just wake up and think everything’s going to be OK with your commute, because it might not be.”

Traffic engineers say 60 percent of the average westbound traffic would need to be diverted off I-90 for a trip from Issaquah to Seattle to take one hour during the bridge project.

King County Metro says it will not reroute any buses. It has warned riders that in addition to the 13 routes that cross the I-90 bridge, routes that use the 520 bridge and I-405 could face delays.

Spokesman Jeff Switzer said Metro will do its best to have backup buses available should regular buses not make it back to the Eastside in time to pick up the next round of riders.

Up to 6 times longer

WSDOT says the best times to travel will likely be before 7 a.m. and after 7 p.m. From there, travel times could multiply to as much as six times what they usually are. Traffic will likely improve from 11 a.m. to 2 p.m. but still be heavier than usual.

Current traffic conditions can be checked online at WSDOT’s website and through its mobile appas well as its live-updated Twitter account.

The 520 floating bridge may still open for boats during the I-90 lane closures. But instead of the usual two hours’ notice boaters must give, WSDOT has worked with the Coast Guard to make sure boaters request openings 24 hours in advance. Phelps said the longer notice and the clumping of boat passages together should reduce the frequency of bridge openings.

Tolls for crossing the 520 bridge will not be waived. Phelps said that WSDOT notified the state Transportation Commission, which sets tolls, on July 1 and July 10 about the upcoming closures.

The lane closures come during the same week that the Mariners will play at home against the New York Mets and the Baltimore Orioles, and the Sounders will play Saturday against Tottenham Hotspur. Also, the Bite of Seattle takes place this weekend at Seattle Center.

Work is high priority

The two, 33-year-old expansion joints being replaced are at the top of a long list of joints that need to be replaced on bridges and highways across Washington, Phelps said. Because there isn’t enough money to replace all the aging joints, the state prioritizes those that look like they need it the most.

Expansion joints fit between the concrete slabs on bridge decks to help the structures withstand drastic changes in the elements. Because concrete can expand and contract, the joints keep the bridge from cracking. The bumps drivers feel and hear as they cross bridges are those joints.

Together, the I-90 expansion joints weigh about 29 tons, the WSDOT said. Crews will drill, jackhammer and saw apart the southern half of the bridge to insert one of the joints during the first stage of the project, then do the same for the northern half.

The lanes being closed will change accordingly, but the same number of lanes and entrance points will be open throughout the project.

All drivers will be able to use the HOV lane when it reopens during the last half of the replacement project.

I-90 express lanes will mostly operate the same hours as usual, but WSDOT warns the lanes likely won’t provide much relief because the westbound entrance to those lanes comes after the construction zone.

If aging expansion joints aren’t replaced in time, Phelps says, the steel plates above them can jut up and pop tires, causing traffic jams and even serious accidents.

A steel plate that popped up on southbound I-5 near Holgate Street in Sodo — just in time for the morning commute — brought Seattle-area traffic to a standstill less than two months ago.

On that day, May 29, a drive from Lynnwood to Southcenter took two hours because of backups that were more than 10 miles long.

The life span of the joints depends on wear and tear, Phelps said, and because the Eastside population has grown exponentially since the I-90 joints were first installed, engineers have noticed they’ve deteriorated faster in recent years.

“We’re constantly keeping an eye on our infrastructure so we can replace what’s most important now,” Phelps said.

Alexa Vaughn: 206-464-2515 or On Twitter @AlexaVaughn.

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