Since construction began in 2016, Sound Transit has used a mix of project delivery models and multiple construction teams to build the extension’s surface and underground track sections, stations and other systems. Participants in the soon-to-be-open segment include the Shimmick/Parsons joint venture, Atkinson Construction, Stacy Witbeck, Max J. Kuney Co. and the Kiewit-Hoffman joint venture.

The extension’s remaining major elements, under the construction baton of Kiewit-Hoffman, include a connection with Sound Transit’s existing north-south 1 Line at the Chinatown/International District station; conversion of a reversible express lane on the Interstate-90 floating bridge into a two-track right-of-way and two stations on Mercer Island.

HDR, Jacobs and the STV/Mott Macdonald joint venture are providing construction management services for the East Link extension under separate contracts.

In addition to pandemic-related supply chain issues and a 140-day strike by the area’s concrete delivery truckers, the East Link extension’s progress has been challenged by quality issues with the fabrication and installation of several dozen cast-in-place plinths on both sides of the I-90 bridge.

There was also cracking and flaking, or spalling, of several precast concrete blocks on the bridge. The additional time to investigate and rectify the issues contributed to pushing completion of extension’s remaining sections to 2025.

Under a separate $1.53-billion design-build contract, the Stacy Witbeck/Kuney joint venture is extending 2 Line service to downtown Redmond with a 3.4-mile, three-station segment, also scheduled for completion next spring.