The Santa Clara Valley Transportation Authority (VTA) has chosen a single-bore tunnel design for the BART Silicon Valley extension after an independent peer review. Experts from national transit agencies evaluated options and found the single-bore plan offered the best balance of safety, cost, and feasibility.
The decision directs VTA to advance design work toward 60 percent completion and keep the project on schedule for construction. The extension will add five miles of new track through Santa Clara and San Jose, connecting regional destinations while limiting surface disruption.
VTA engineers will manage the tunnel boring machine now owned by the agency. A team from Herrenknecht will support field operations to maintain productivity and safety.
The review panel advised VTA to improve cost forecasting and risk management and to continue close coordination with BART. The agencies have agreed to resume regular updates to strengthen oversight as construction preparation continues.
The project’s estimated cost stands at $12.2 billion. Early work at the tunnel portal in Santa Clara is already underway, keeping the extension on track for later this decade.