The Santa Clara Valley Transportation Authority (VTA) recently released a detailed cost report analyzing the twin-bore tunneling method for the BART Silicon Valley Phase II (BSVII) Project. Developed in response to questions raised by the VTA Board of Directors, the report provides a clear and transparent look at the costs associated solely with the twin bore approach.

“This report underscores that we are on the right track,” said Carolyn Gonot, VTA general manager and CEO. “The findings reaffirm that the single bore approach remains the most cost-effective method to bring BART service into the heart of Silicon Valley.”

According to an agency release, the VTA Board of Directors and the community have consistently supported the single bore design, recognizing its advantages in minimizing community disruption, reducing surface construction impacts, and delivering transit more efficiently.

Key findings of the report highlight a higher cost for the twin bore due to the large cut-and-cover stations, challenging construction factors, and additional time required for design.  

VTA Addresses Twin Bore Cost Analysis

The agency noted that the newly released report focuses exclusively on the twin bore method, offering an in-depth analysis and view of costs to ensure clarity and transparency for stakeholders and the public.

“Our board has raised the question of whether a design change to the twin bore would be cheaper and safer. This report is a direct response to that question,” said Tom Maguire, VTA chief megaprojects delivery officer. “It gives a clear picture of the costs involved with a twin bore tunnel and reinforces why the single bore approach remains the best choice for this project.”

Throughout the review process, the agency continued advancing the BSVII project, which will extend BART service six miles from the Berryessa/North San José Station through downtown San José to Santa Clara, by pursuing cost containment and cost avoidance strategies.

“We’ve been hard at work to keep BSVII on schedule and on budget, and this report validates the strategic decisions that are moving this critical project forward,” Gonot said.