The Santa Clara Valley Transportation Authority is all in on its plans to build a roughly five-mile long tunnel under downtown San Jose and Santa Clara for its Silicon Valley BART extension after officials announced this week it had purchased a $76 million tunnel boring machine.
The custom-made machine was ordered from German company Herrenknecht and will be manufactured, assembled and tested in Germany before its disassembled and shipped in pieces to Santa Clara County. It will then be reassembled at the project’s West Portal/Newhall Yard located between the San Jose airport and Santa Clara University where work is expected to begin in 2025.
The six-mile BART extension will connect the Berryessa Transit Center in north San Jose to downtown and Santa Clara with four stops and could carry more than 50,000 passengers on weekdays to other parts of the Bay Area by 2040, according to VTA estimates.
“There’s no turning back now,” San Jose Mayor Matt Mahan said in a news release. “This purchase cements our commitment to connecting the entire Bay via rail. When complete, BART to Silicon Valley will unlock tremendous transit capacity and economic growth for our region.”
VTA estimates the tunnel boring machine will take approximately three to four years to dig the five-mile-long, nearly 54-foot in diameter tunnel that is expected to be the largest single bore transit tunnel in the world. The machine, which has been likened to a mechanical earthworm, will be capable of digging 30 to 40 feet a day and will be extracted on the east side of Highway 101 near Las Plumas Avenue.
“This is a momentous next step,” Santa Clara County Supervisor Cindy Chavez said in a statement. “It represents more than just moving dirt — it represents being one step closer to moving people to jobs, to family and to the entire region. Thousands of jobs will be created during construction, with thousands more fueling this transit-oriented development.”
Plans for a single-bore tunnel have been met with criticism throughout the BART extension planning process from individuals who said the design will lead to ballooning costs. Just last month, VTA officials said the project was facing yet another delay with a new estimated completion date as late as 2036 and a price tag of up to $12.2 billion — more than twice the original estimate.
An oversight group was launched last month in response to the skyrocketing costs and added delays. In 2014, transit officials estimated the project would cost $4.7 billion and open in 2026.
VTA opted for the single-bore design to prevent having to dig up large stretches of Santa Clara Street in downtown San Jose. The alternative twin-bore design would have required creating shallower side-by-side tunnels by digging up the street.
The transit agency is expected to hold a naming contest for the massive machine.
Other cities that have used tunnel boring machines for projects have also held naming contests for the large devices. In 2021, Seattle Public Utilities named its tunnel boring machine Mudhoney. Other popular nominations included Sir Digs-a-lot and Boris the Plunger. Last month in Glasgow, a student won a contest to name a much smaller tunnel boring machine, Cruella de Drill.