VTA sticking with single tunnel BART plan after report reveals high cost of twin bore design

SAN JOSE, Calif. (KGO) -- In an effort to make the best financial decisions for the Silicon Valley BART Expansion project, the VTA board discussed potentially switching from a single tunnel to twin tunnels.

A new 78-page report analyzes both approaches and found the current design is substantially more expensive and more impactful than the other.

VTA's Silicon Valley BART expansion will be one of the most expensive projects in the Bay Area, coming in at a price tag of nearly $13 billion.

VTA Chief Megaprojects Delivery Officer Tom Maguire says when you're working with that kind of money, making the right and most cost-effective decisions is critical.

The report found the twin bore design is not only more expensive, but it would create significantly more construction issues for Downtown San Jose.

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Maguire says this report affirms confidence in the single-bore approach that is already underway.

"This is a very innovative approach," Maguire said. "It's an approach that's been done successfully outside of North America, but it will be the biggest transit tunnel in North America. So we think it's the right project, and we chose it because of all the positives."

A single-bore tunnel is just that, a 53-foot-diameter tunnel that spans five miles -- to connect BART from Berryessa to Santa Clara.

It will contain both tracks, the stations and infrastructure and construction will take place on VTA property.

"So, we won't build the stations by digging up the street or the sidewalks like other cities do," Maguire said. "We'll build those stations in off-street properties and allow traffic and commerce to continue to flow downtown during construction."

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The report found the impacts from construction through Downtown San Jose is one reason why the twin-bore approach is not feasible.

Maguire says the twin-tunnel design is an older version of transit that is not suitable for the South Bay.

"Particularly our groundwater and our soil that really make the single bore, the innovations of large single bore particularly well-suited to our project, and it's the right way to go," Maguire said.

"Not only that, the twin bore is actually $600 million more than it would cost already, right?" ABC7 News South Bay Reporter Dustin Dorsey asked.

"That's right," Maguire said. "And this is a time we need to be saving money, not spending more."

The report, as well as cost-effective strategies for the single-bore design will be discussed at VTA's BART expansion oversight committee meeting on Thursday.