The Clear Choice for the Future of BART Silicon Valley, A Smarter Design for Faster, Cost-Effective Transit

A single-bore tunnel is the smarter, faster, and more community-friendly way to complete the final phase of VTA’s BART (Bay Area Rapid Transit) Silicon Valley Extension, according to a new study released this week.

The findings show that this design is more cost-effective, quicker to build, already approved, and far less disruptive to downtown San José and its business community. It keeps streets open, supports the local economy during construction, and brings BART to Santa Clara County sooner.

After years of technical analysis, public input, and federal review, the Santa Clara Valley Transportation Authority (VTA) continues to advance the single-bore tunnel as the preferred design for extending BART through downtown San José to Santa Clara. Compared to a twin-bore tunnel, the single-bore option offers clear advantages and is significantly less expensive and less risky.

Minimizing Disruption, Maximizing Progress

Importantly, the single-bore tunnel has been approved since 2018. The VTA and BART Boards of Directors endorsed the plan, and the Federal Transit Administration has issued its Record of Decision, clearing the way for engineering and construction to proceed. Switching to a twin-bore design would require restarting environmental reviews, repeating engineering work, and buying new tunnel boring machines - delaying progress and increasing costs.

The single-bore approach also minimizes disruption to downtown San Jose businesses. Unlike "cut-and-cover" construction—which involves digging up streets and rebuilding them, causing noise, full street closures, and utility relocations—the single-bore tunnel places infrastructure deep underground. This means fewer surface impacts, less traffic disruption, and a better environment for local businesses to operate during construction.

VTA remains committed to delivering a world-class transit connection that meets today’s needs and supports tomorrow’s growth. The single-bore tunnel is how we get there—efficiently, responsibly, and with our community in mind.