SF BART Chooses Smarter Tunnel Design for Silicon Valley
BART selects 58-foot single-bore tunnel design for San Jose extension, saving $700 million
BART Picks Single-Bore Tunnel for Silicon Valley
BART's extension into downtown San Jose will use a single-bore tunnel design that's expected to save $700 million and speed up construction, transit officials said Tuesday. The Valley Transportation Authority selected the 58-foot-diameter tunnel as the preferred alternative for the 6-mile Phase II extension, which will add four stations to the regional rail network. Carolyn Gonot, General Manager and CEO of VTA, said the approach represents a smarter option for the region, though officials haven't released a specific construction timeline.
Why VTA Changed Course
The single-bore design marks a shift from traditional twin-bore tunnel approaches that transit agencies have historically used for rail projects, according to VTA. Officials began evaluating tunnel alternatives in 2024 as part of ongoing environmental review for the extension, which broke ground in June 2020. The design uses side platforms within a single large tunnel rather than separate tubes for each direction of travel. Transit agencies typically choose tunnel configurations based on cost, construction time, and community impact, though specific ridership projections for the extension weren't available.
Cost Savings and Construction Benefits
The single-bore approach will save approximately $700 million compared to a twin-bore alternative, VTA officials said, though they didn't disclose total project costs. The 5-mile tunnel will be bored through downtown San Jose using proven technology that's been successfully deployed in Seattle's light rail system and London's Elizabeth Line. Officials said the larger single tunnel reduces surface disruption during construction and shortens the overall build timeline by years. The design includes emergency walkways, cross-passages, and ventilation systems that meet safety standards, according to the transit agency.
Timeline Remains Unclear
VTA hasn't announced when tunnel construction will begin or when the extension will open to riders. The project is undergoing environmental review as part of the design selection process, officials said. Transit agencies typically notify riders several weeks before major construction milestones, but whether VTA will provide advance notice for tunnel boring wasn't specified. The extension will connect the existing Berryessa station to downtown San Jose and Santa Clara.
What Riders Need to Know
The four-station extension will bring BART service deeper into Silicon Valley's employment centers, though officials didn't say how many daily riders they expect. Community and stakeholder responses to the tunnel design weren't immediately available. Riders can track project updates and plan trips on the existing BART network through Moovit, which provides real-time information for Bay Area transit services.
