All lanes of Interstate 5 will close north of Tacoma during the night this Friday and Saturday, so builders can install some of the world’s longest concrete I-beam girders.

Contractors are building an overpass and roundabout for the Puget Sound Gateway, a $2 billion bundle of extensions for highways 167 and 509 that’s been on the drawing board for two decades. The Legislature in 2015 directed part of a gas-tax increase to complete the project by 2028. Tolls will be charged as well.

The new road capacity will serve the Port of Tacoma, Seattle-Tacoma International Airport and the Green River warehouse area to “eliminate a bottleneck in the national supply chain,” Washington state Transportation Secretary Roger Millar wrote in a federal grant application that won $73.6 million.

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The beams to be delivered, about 220 feet long, will replace the 70th Avenue East bridge in Fife with a bigger overpass, where a new Highway 167 spur will stretch east-west between Puyallup and the Port of Tacoma.

Concrete abutments already are in place on either side of I-5. The state chose extra-long girders to cross the freeway, because shorter spans would require a support column in the median, which would force prolonged I-5 lane changes and closures, according to the Washington State Department of Transportation (WSDOT).

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Both directions of I-5 will close overnight on Friday and Saturday, with the first lanes barricaded at 8 p.m. and total shutdowns by 11 p.m. Lanes will gradually reopen starting at 8 a.m., with full traffic restored by noon.

Fife-to-Tacoma traffic on I-5 clogs even on normal weekend mornings. Detour options during the night closures will be abnormally long, because I-5 exits in the area are 5 miles apart. WSDOT suggests using Highway 99 parallel to the freeway, or skip Tacoma by sweeping through Puyallup via highways 512, 167 and 18.

“There’s no easy way to take 10 travel lanes and squeeze them down to four on 167, or even Highway 99,” said Cara Mitchell, WSDOT regional spokesperson.

This fall, another 30 extra-long girders will be installed over the Puyallup River and a rail yard, to form a permanent southbound bridge for I-5. This work won’t block mainline travelers, but the temporary collector-distributor lanes, southbound on an old bridge, will close during girder delivery.

That work is expected sometime in October, subject to weather and any COVID-19-related schedule complications.

Those girders vary from 207 feet to 223 feet, which ties the world record in the Netherlands, said Bijan Khaleghi, state bridge design engineer. The Dutch bridge, built in 2014, replaced a drawbridge over a ship canal.

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Girder lengths are limited mainly by what can be trucked. They’re possible here because Concrete Technology Corporation, the area’s leading supplier, is only three miles away.

The previous U.S. record I-beams were 205 feet long, fabricated by Concrete Technology and installed in 2011 where rebuilt Highway 99 passes over a freight-train track in Seattle’s Sodo area.

For this year’s Tacoma-area projects, shale and slate were imported from North Carolina to create a lightweight concrete mixture, reducing weight by 20%, said Vice President Steve Seguirant. That got the weight down to 247,000 pounds per girder.

Internal steel cables through the I-beam were tightened in the casting yard, a step known as prestressing, that reinforces the concrete. Extra rebar was laced into the beam ends so they won’t crack under the pressure, a technical article says.

Why bother making monster girders?

“Crossing the Puyallup River, as well as the railroad beneath, are environmentally challenged, so we don’t want construction and columns in the middle,” said Khaleghi.

The 200-plus foot girders keep WSDOT out of the railroad yard, where owners might otherwise demand an expensive land deal, or restrict construction hours if the state had to plant columns between train tracks.

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That rail-yard crossing, along with the spans over the Puyallup River, will become the new southbound mainline, of four general lanes and one carpool lane. Southbound traffic now squeezes into three lanes on WSDOT’s new northbound I-5 bridge.

In addition to the Gateway and Tacoma projects, WSDOT is widening I-5 near Joint Base Lewis-McChord, a chronic bottleneck.

Washington state’s traffic growth, which rose 7.4% from 2014-18, conflicts with Gov. Jay Inslee’s recent presidential-campaign theme to fight climate change, while Millar has preached nationally “we can’t build our way out of congestion.

Millar insists the Gateway program is compatible with environmental values.

“We’re building four-lane tolled highways, as opposed to six-lane freeways,” he said this month. Tolls would dampen travel demand and raise $180 million toward the $2 billion budget, at rates to be determined by the state Transportation Commission.

He’s hopeful the new lanes promote infill growth and jobs for South King County. “What I’d hate to see is sprawl development accelerate, so everybody jumps in their car and drives to South Lake Union,” he said.

Climate Solutions, a Northwest nonprofit that promotes clean energy, said it hasn’t analyzed Gateway specifically but warns that state highway growth will cause “induced demand,” the phenomenon in which new roads entice more traffic and carbon pollution. With limited dollars, Washington leaders should focus on more transit options, safe walk-bike routes, and vehicle electrification, said Leah Missik, the group’s transportation-policy manager.

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Millar said Gateway should reduce commute distances for workers in south King and north Pierce counties, who take circuitous routes now, allow new industries and businesses south of the airport, and reduce hourlong truck delays for produce, grain and other cargo arriving from inland to the Port of Tacoma.

A WSDOT cost-benefit analysis asserts Puget Sound Gateway will reduce tailpipe carbon emissions a total 67 million tons the first four years, by reducing congestion and driving distance.

“We can provide direct connections that make access much more efficient. If we combine that with decarbonizing, we’ve got a winner,” Millar said.