Despite rain showers in the forecast, the Washington State Department of Transportation says contractors will go ahead with weekend replacement of worn-out steel expansion joints along southbound Interstate 5 in Sodo.

Only one lane there will stay open for traffic, from 10 p.m. Friday until 5 a.m. Monday, so traffic jams are likely to stretch back through downtown.

What’s more, WSDOT says the I-5 express lanes will close in both directions all weekend from 8:30 p.m. Friday until 4:30 a.m. Monday. This shutdown is to start building a bus and carpool-lane connection from Highway 520 to the I-5 express lanes, that continues to Mercer Street, where transit could become quicker for South Lake Union commuters.

And overnight maintenance at the Highway 99 tunnel will close both directions from 10 p.m. Friday until 6 a.m. Saturday. Highway 599 in Tukwila might also close overnight Friday southbound, depending on weather.

The National Weather Service predicts a 50-50 chance of afternoon showers Saturday, followed by a possible quarter- to half-inch of rain Saturday afternoon and Sunday.

However, crews on I-5 will “tent the joints” in an effort to keep those dry, said Tom Pearce, project spokesperson for WSDOT.

Workers will also bring sandbags and air blowers in case water leaks in, he said.

They will be replacing steel joints near Spokane Street with silicone joint fillers, similar to those built in 2007 on the northbound side. Dry conditions are required to rebuild the edges, using polyester concrete, to improve old decks that were built in the 1960s. Expansion joints are gaps that allow the road decks to expand in hot weather.

Contractors canceled two weekends of work because of rain, before accomplishing a first round of joint work May 21-22. As a last resort, Pearce said, they would use conventional concrete in a downpour this weekend, as a temporary move until the synthetic concrete can be applied.

“We’re running out of extra weekends. We need to get the work done,” he said. An additional 14 weekends of lane shutdowns are expected through October.

Sound Transit light rail, from North Seattle to SeaTac, is expected to run on normal schedules, with trains every 10 minutes most hours. But in July, the agency says it will reduce service to 20-minute frequency during a tile replacement at Columbia City Station, at the same time WSDOT continues its weekend closures.

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