The Santa Clara Valley Transportation Authority (VTA) has confirmed the large single bore as the preferred tunnel configuration for BART Silicon Valley Phase II, following a peer review conducted by tunneling and transit experts from major transit agencies across the country.

The VTA Board of Directors, in a special meeting recently, heard an extensive presentation on the peer review and its recommendations on moving forward with the largest public infrastructure project in Santa Clara County.

Following the discussion, the board voted in favor of the single bore as the most viable option, offering the best balance of constructability, feasibility, and lower overall risk. According to an agency release, it avoids the high cost, complexity, and downtown disruption associated with an alternative concurrent tunneling approach of using two boring machines.

This alternative would have required a cut-and-cover excavation in the heart of San Jose. The board’s decision allows VTA to advance project design towards 60% and meet the projected revenue service date.

The panel also included recommendations to ensure greater cost estimation, accuracy and budget alignment, reduce schedule delays and manage tunnel risk.

VTA Reinforces Tunneling Team and Industry Partnerships

With VTA now owning the Tunnel Boring Machine (TBM), the agency assumes full responsibility for its performance. To manage this risk, VTA will deploy a top-tier tunneling team and embed Herrenknecht engineers to support operations and reduce delays.

The panel also highlighted the limited pool of qualified contractors and skilled labor for large diameter tunneling. VTA will continue early engagement with the industry to secure experienced construction teams and develop a contract strategy toincreasebidder participation.

Lastly, according to the release, the peer review reinforces the importance of a strong VTA-BART partnership. Both agencies have agreed to reestablishing regular touchpoints and prioritizing communications between agencies.