After years of technical analysis, public input and federal review, the Santa Clara Valley Transportation Authority (VTA) recently selected the single-bore tunnel as the preferred design method for the five-mile portion of the BART Silicon Valley Phase II (BSVII) tunnel. This $12.7 billion project is a six-mile, four-station extension of the regional BART system from downtown San Jose to the city of Santa Clara.
The VTA Board of Directors said the single-hole method avoids the high cost, complexity and downtown disruption associated with an alternative concurrent tunnel approach of using two boring machines, an alternative that would have required a cut-and-cover excavation in the heart of San Jose.
VTA says going with a single hole, which is estimated to cost about $3 billion, is the “most viable option, offering the best balance of constructability, feasibility and lowest overall risk.” This decision allows VTA to advance the project’s design to 60 percent, stay on a critical path for tunnel construction and meet the expected revenue service date, officials say.
Before construction begins, VTA will go through a competitive bidding process to hire a new tunneling contractor. At this time, there is no short list of contractors, says VTA spokeswoman Stacey Hendler Ross. “Following an initial round of industry outreach conducted at major tunneling conferences earlier this year, VTA met with ten heavy civil construction and tunneling contractors to discuss delivery methods, contract packaging size, scope and other contract areas,” he says.
VTA says it plans to release the request for proposals for the new tunnel contract in the first quarter of 2026 with a contract award expected in the second quarter of 2027 and tunnel construction finally starting in 2029.
A joint venture of Kiewit Infrastructure West, JF Shea Construction and Traylor Brothers (KST) was originally selected in 2022 to lead construction of the tunnel, but after receiving repeated proposals exceeding twice the project’s budget, VTA decided last June to seek another tunnel contractor.
“Based on initial industry feedback received earlier this year and the work done to date, VTA plans to issue a new tunnel procurement to increase bid competitiveness, including revising contract terms, risk-sharing opportunities and contract size,” Ross said. “Additional details of what we will be asking for will be included in the request for proposals. We will also be doing additional industry outreach over the coming year.”
The Kiewit Shea Traylor Joint Venture is still on the project, building early construction activities, including the TBM launch structure.
Looking ahead, one of the biggest challenges with building a tunnel in the South Bay is the difficult ground conditions and high water table, says Sarah Wilson, BART Silicon Valley’s Phase II construction manager.
“We’re basically going to operate a train system in five stories of space underground and at the same time keep the excavation safe in difficult ground and groundwater conditions,” says Wilson. “Keeping this operation running smoothly and safely requires experience and management of the highest caliber.”
Much of the current work on the BSVII project is taking place at the Newhall Yard and West Portal site, located on the border of San Jose and Santa Clara, just west of the San Jose Airport. Crews are currently constructing the tunnel boring machine (TBM) launch structure, a massive excavation that reaches more than 130 feet deep at one end and rises to the surface. This will be the starting point for the TBM’s journey once it arrives from Germany, and later the place where trains will enter and exit the tunnel.
To prepare the tunnel site, crews are installing reinforced underground retaining walls constructed of huge rebar cages, some weighing up to 300,000 pounds. Excavation of the launch structure is also underway, with hundreds of truckloads of soil being hauled in daily as crews shape the tunnel’s future gateway.
In addition to KST completing early construction activities, there are several crews working on BART Silicon Valley Phase II. The program management team is a joint venture of HNTB and WSP, the general engineering consultant is a joint venture of Mott MacDonald and PGH Wong, and construction management services are provided by Bechtel. Ross says there will be several more contracts to build the rest of the BSVII project in the coming years.
The BSVII project is the largest public infrastructure project in Santa Clara County. With four stations, the project will serve 55,000 weekday commuters when complete.
