MERCER ISLAND — For a couple of years already, Interstate 90 travelers have seen construction workers toil in the former express lanes, striving to repair flawed track supports along Sound Transit’s future light-rail extension.

But after futile attempts to adjust, jackhammer or patch these pieces like a dentist filling teeth, they’ve changed tactics.

Contractors will now rebuild the nearly 5,500 concrete blocks, known as plinths, from scratch, a task that jeopardizes Sound Transit’s goal to begin train service across Lake Washington in spring 2025. Long stretches of the deck have been stripped to bare pavement, while tents provide weather protection for new components being installed.

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This second effort by the Kiewit-Hoffman joint venture covers a four-mile area of Seattle and Mercer Island, on decks where freeway structures run above ground. 

The contractor team decided in late September, after mortar failures and a forensic investigation, that the best option is to start over, according to Sound Transit. More than half the plinths were demolished and some rebuilds begun last fall, deputy CEO Kimberly Farley notified board members in November.

Sound Transit’s grand opening target of 2025 was announced after plinth troubles ruined attempts to finish the whole Eastside corridor, also known as the 2 Line, by mid-2023 and then by spring 2024.


Demolition of the original plinths is nearly complete, and the track rebuilds will expand to six work zones this month, staff reported Thursday in an update to the board.

Contractors added to their workforce in April, and the agency’s managers have kept in daily contact, said Ron Lewis, Sound Transit’s executive director for design, engineering and construction management.

“They made a concrete pour on Tuesday this week, and more are scheduled in the coming days,” he said.

However, he also said track rebuilding has gone slower than planned, and unless the pace quickens immediately, Sound Transit will miss the grand opening goal.

Project managers say they first became aware of plinth problems in 2019, such as too much or too little steel rebar near the concrete surfaces, some voids or plinths not tall enough. They didn’t reveal a schedule crisis until April 2022, after trying adjustments such as mortar patches and surface grinding.

Disappearing tracks

At left, tracks for Sound Transit’s light-rail 2 Line between Seattle and the Eastside are seen in April 2022. At right, as of last week, they have been removed.

These 5,455 plinths sit upon fixed, mainly overland deck spans of I-90. A second, less-vexing problem involves precast concrete blocks on the floating bridge that are structurally sound but need new, stronger nylon bolt inserts where the rails are fastened. A third type of track tie, where concrete blocks are nestled within gravel ballast, is doing fine.

Transit executives have been chastised by outside experts for not airing the bad news more quickly about the multiple challenges facing delivery of the nation’s largest transit expansion program. But on Thursday, board member Kent Keel of University Place praised the staff and new CEO Julie Timm for increased transparency in recent months.

Kiewit’s headquarters in Omaha, Neb., did not reply to a request for comment.

“Our construction contractor has been working with us to resolve these issues,” Sound Transit chief of staff Brooke Belman said last summer.

Last year, Sound Transit also acknowledged that its quality control program wasn’t robust enough, and remote work required during the early COVID pandemic made it more difficult to inspect and oversee the project. But the same report said the responsibility lies with contractors. “On the E130 project, the contractor’s quality control program did not perform properly, as demonstrated by the extent of the quality defects in the track plinth construction,” Sound Transit said.

It’s not clear yet how much extra money Kiewit might claim, or what penalties Sound Transit may try to charge. Typically, government sponsors and builders agree to finish the work before hammering out who pays for megaproject overruns, by negotiations or lawsuits.


But the board last month did approve a potential $14 million contract increase to compensate for the nylon-fastener issue. The causes for this flaw are still being investigated. That boosts the I-90 segment construction contract to $736 million from Seattle to South Bellevue. And another $17 million was approved for Jacobs Project Management to continue its consulting oversight of the I-90 segment construction.

Once a workable trackway is complete, additional weeks are necessary to test the train fit, power and signals, followed by at least 60 days of full-speed practice trips. During this break-in period, engineers must also confirm that their exotic transition joints keep the rails parallel and flex precisely as designed, before trainloads of people travel 50 mph between fixed roadway decks and movable bridge pontoons. This is the world’s first rail transit on a floating span.

Ironically, the plinth mess might increase the odds that Bellevue and Redmond travelers get to use a local Eastside line first in spring 2024 — between South Bellevue and Redmond Technology stations — before Lynnwood train service begins.

Before they can fully serve Lynnwood, transit operators need a finished I-90 crossing, so trains can move from a new Bellevue maintenance base to the University of Washington, Northgate and Lynnwood. Until then, Lynnwood can’t receive the promised capacity of one train every 4 minutes, transit officials say. Their fear of a crowded Lynnwood line has generated political momentum to open the so-called Eastside Starter Line first.

The whole $3.7 billion, 14-mile extension, from International District/Chinatown Station to Redmond Technology Station, was approved by voters in a 2008 sales-tax measure. The campaign promised a 2020 opening, which slipped three years amid route-alignment disputes between Sound Transit and Bellevue.

Lewis and Belman also reported Thursday that construction for both the Lynnwood and downtown Redmond extensions is showing “positive float,” meaning the crews are on track to finish days ahead of schedule.

That progress raises a question for later, Lewis said. If the downtown Redmond job keeps humming along, and the I-90 rework is slow, it might make sense to combine two more train stops at downtown Redmond and Marymoor Park with the rest of the eight-station Eastside starter line.