Will VTA change its tunnel design for the San Jose BART extension after completing a new cost estimate?

With BART’s Silicon Valley extension expected to cost upwards of $12 billion, the Santa Clara Valley Transportation Authority is conducting a new cost analysis of a different approach — the controversial twin-bore tunnel design — largely to assuage vocal critics who feel the agency has been moving in the wrong direction on the project for years.

In 2018, VTA decided on the single-bore tunnel design that calls for one massive tunnel deep underground that will deliver passengers through the six-mile, four-station extension from the Berryessa Transit Center in north San Jose, through downtown and up to Santa Clara. The innovative approach would make it one of the nation’s largest subway tunnels.

Since then, critics have questioned whether that was the right and most cost-effective option and have pleaded with the transit agency to revisit the twin-bore design, which would have shallower, side-by-side tunnels. While that approach may be more standard in the transit world, it would require VTA to dig up swaths of the streets, disrupting businesses in downtown San Jose.

After nearly six years, those critics are now making some headway as Tom Maguire, VTA’s chief megaproject officer, told The Mercury News the agency is moving forward on analyzing the cost of the twin-bore design. The agency currently only has an old, very preliminary cost estimate for the twin-bore option that Maguire called a “much less complete design.”

“I think what matters is that we give a real apples-to-apples comparison,” he said. “That spirit of a fair comparison is something that we carried through the five different peer reviews on the tunnel design that got us to this point, and so we want to make sure that we are comparing the twin bore as it actually would have to be constructed in San Jose, not as an abstract concept.”

Santa Clara Councilmember Suds Jain, who sits on VTA’s Board of Directors, was among the first to sound the alarm — especially in light of ballooning costs. Since 2014, the cost of the megaproject has risen from $4.4 billion to more than $12 billion. The timeline also has been pushed back from a 2026 opening to 2037.

Jain said he asked VTA officials to get a new cost estimate on the twin-bore design because “the conditions have changed so dramatically” since the single-bore option was approved.

One of those changes is the width of the tunnel itself. The original single-bore plan was to create a 43-foot-wide tunnel with the train tracks stacked one on top of the other. But those plans were eventually scrapped as the agency opted for a 48-foot-wide tunnel that has side-by-side tracks, eliminating confusion for riders about whether they’re on the right platform.

The change led to the agency last year purchasing an even bigger custom-made tunnel boring machine that’s 54 feet in diameter. It came with a whopping $76 million price tag, and VTA estimates it will be one of the largest machines ever built at roughly five stories high.

Even though the agency has already made the hefty purchase, Jain believes they can still switch gears.

“If you think about it, $76 million is almost a half of percent of the cost of the project,” Jain said. “If you can save 5% by doing dual-bore, isn’t that a win?”

Aside from costs, Jain also has safety concerns. Under the single-bore design, the platforms in downtown San Jose and at Diridon Station are expected to be 75 feet below ground.

“The inconvenience to passengers to get on elevators to go 8 or 12 stories is tremendous,” Jain said.

If there’s an emergency, the councilmember worries about riders’ ability to evacuate safely from such a depth.

Palo Alto Councilmember Pat Burt, who also sits on the board, said that while he doesn’t think the agency is at a point where they want to “completely reevaluate switching to a twin-bore,” they do want “updated information.”

“We want to have some form of an updated understanding of comparing and revalidating that the decision that was made remains the right one,” he said. “It (single-bore) does seem to have the backing of the VTA, and that’s what’s very crucial, and we don’t want to do anything to undermine that backing.”

However, if there is a drastic cost difference between the two, Burt said the agency might want to reconsider.

Maguire declined to say when the analysis would be complete but made it clear that the cost shouldn’t be the only factor in changing course.

“My goal with this analysis and with this dialogue is to make sure policymakers and the public understand all the factors that led to this decision, including cost and also including disruption and technical feasibility,” he said. “It’s easy to say you should do it differently when you’re not accountable to every single person who lives and works in downtown San Jose and Little Portugal and Santa Clara that this job be done safely and with minimal community disruption.”

Jim Schmidt, a local transit advocate who has been asking for the cost estimate of the twin-bore design for years, was ecstatic to hear that the agency was finally listening to some of the community’s concerns. On the other hand, he still worries about VTA conducting the analysis itself, given its investment in the single-bore design.

“It would be better in my view if the work was done by an independent party to ensure objectivity,” he said.  “We’ll just have to hope the agency is careful in the analysis and does it very professionally.”