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10/20/2025
The Santa Clara Valley Transportation Authority (VTA) in California, during a special meeting held Oct. 17, confirmed the large single bore as the preferred tunnel configuration for the $12.7 billion Bay Area Rapid Transit (BART) Silicon Valley Phase II project.
The board's approval followed a peer review conducted by tunneling and transit experts from major transit agencies across the country, VTA officials said in a press release.
VTA's BART Silicon Valley Phase II Extension is a 6-mile, four-station addition to BART, connecting from Berryessa-North San Jose Station through downtown San Jose to Santa Clara. This includes 5 miles of subway, with underground station platforms at 28th Street-Little Portugal, downtown San Jose and Diridon stations, and a ground-level station in Santa Clara. A train maintenance and storage facility will be co-located in San Jose and Santa Clara.
The board’s Oct. 17 decision allows VTA to advance project design toward 60%, stay on a critical path to tunnel construction and meet the projected revenue service date, VTA officials.
The panel also included recommendations to ensure greater cost estimation, accuracy and budget alignment, reduce schedule delays and manage tunnel risk.
With VTA now owning the tunnel boring machine, the agency assumes full responsibility for its performance, agency officials said. To manage the risk, VTA will deploy a tunneling team and embed Herrenknecht engineers to support operations and reduce delays, they said.