Expert panel backs single-bore tunnel plan for San Jose BART project

(UI) — The Santa Clara Valley Transportation Authority (VTA) has confirmed the large single-bore configuration as the preferred tunnel design for the BART Silicon Valley Phase II project, following an independent peer review by tunneling and transit experts from agencies across the country.

During a special meeting, the VTA Board of Directors voted in favor of the single-bore approach, which was deemed the most viable option for balancing constructability, feasibility, and project risk. The design also avoids the high cost and disruption of a dual-bore, cut-and-cover alternative through downtown San Jose.

Construction of the tunnel boring machine (TBM) launch portal is already underway in Santa Clara. The board’s decision allows VTA to advance design to 60% completion and remain on track for the project’s revenue service date.

The review panel issued several recommendations to improve cost estimates, maintain budget alignment, and manage tunneling risks. With VTA now owning the TBM, the agency assumes full responsibility for its performance and plans to deploy a top-tier tunneling team, including embedded Herrenknecht engineers, to oversee operations and mitigate potential delays.

The panel also cited challenges related to the limited number of qualified large-diameter tunnel contractors and skilled workers. To address this, VTA will continue early engagement with the tunneling industry to attract experienced bidders.

VTA and BART have agreed to strengthen coordination, restoring regular touchpoints and prioritizing communication to support project delivery.

“VTA remains committed to delivering this critical regional project with expert guidance, sound engineering, and continued collaboration,” the agency stated.

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