VTA wants to build world's biggest subway tunnel in downtown San Jose

A mockup of a proposed BART station in downtown San Jose. A mockup of a proposed BART station in downtown San Jose. Photo: Santa Clara Valley Transit Authority Photo: Santa Clara Valley Transit Authority Image 1 of / 3 Caption Close VTA wants to build world's biggest subway tunnel in downtown San Jose 1 / 3 Back to Gallery

For $5.6 billion, the Santa Clara Valley Transit Authority wants to build the world's biggest subway tunnel to ferry passengers into the yet-to-be-built downtown San Jose BART stations, according to a report from the Mercury News.

VTA is calling for a 56-foot-wide tunnel-boring machine to carve out a roughly five-mile long subway line into downtown San Jose. The plan, as of now, would utilize the single-bore method favored in some European countries instead of the traditional cut-and-cover method of subway implementation. Theoretically, single-bore is preferable to cut-and-cover; cut-and-cover requires tearing up streets, whereas single-bore allows life to proceed with relatively little interference.

The unprecedented size of VTA's proposed tunnel appears to be complicating matters. Via the Mercury News:

One of VTA officials’ main selling points to the public for the single-bore design in 2018 was that it would be cheaper and quicker to build than typical methods, which require boring two smaller holes. But that promise may not hold up.

Last year, VTA officials increased the extension’s estimated cost by $900 million and pushed back their timeline for completing it by as much as four years — from a $4.7 billion project finished in 2026 to a $5.6 billion one that could open in 2029 or 2030.

Because the proposed tunnel would be constructed 100 feet below street level, the project also calls for "high-speed elevators" to bring passengers to the platform.

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Advocates for the project relayed their enthusiasm to the Mercury News.

"We’re Silicon Valley, we can do things the rest of the world doesn’t do," Rod Diridon Sr., the namesake of the future downtown San Jose BART station, told the Mercury News.

On Twitter, however, Bay Area transit enthusiasts roundly lambasted the VTA plan.

"The gall to sell this as Silicon Valley innovation when this will just explode costs, while the far simpler solution of cut and cover is just sitting right there, is really something else," wrote one Twitter user.

"Imagine being the VTA and being so incompetent this is your decision for how to build a subway station," wrote another Twitter user. "Every single person associated with these decisions should be fired, and never allowed near a subway construction project again."

Click here to read the full story from the Mercury News.

Michael Rosen is an SFGATE digital editor. Email: michael.rosen@sfgate.com.