BART Board of Directors voted Thursday to go ahead with the long-awaited extension into San Jose by finally approving a tunneling plan, which puts to rest months of argument with Santa Clara County over what methods to use.

In a 5-0 vote, with one board member abstaining and three absent, the directors gave the nod for a “single-bore” tunnel project that the Santa Clara Valley Transportation Authority says will be faster and less disruptive to San Jose traffic.

Previously, BART planners had wanted to go with a more traditional dual-tunnel approach to the San Jose dig, and the disagreement put the $4.8 billion project into a holding pattern.

As San Jose Mercury news explained in an editorial endorsing the single-bore earlier:

“The technology allows the boring machine to dig deeper underground, without tearing up streets and disrupting traffic flow. It also should cut 10 months off the four-year tunneling phase and drop the total price tag by an estimated $50 million. “The twin-tunnel approach originally supported by BART’s staff would have involved ripping up Santa Clara Street, from Market Street to Third Street, for a period of three years. The “cut and cover” process would have required relocating complex utility networks, frequently causing construction delays.”

The VTA board approved the tunnel plan earlier this month. The Thursday vote also means that the extension may qualify for federal grants that cover nearly a third of its costs.

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Director Thomas Blalock recorded some reservations about the methods, predicting that a single tunnel would result in smaller stations and platforms that BART riders might regret down the line.

“Those platforms are going to limit capacity in Santa Clara County,” warned Blalock. But in the end, he was among those who voted yes on the proposal.

Writing in 2010, transit news site The Source noted that the single-bore method is the result of new technology and larger digging machines:

In recent years, even larger tunneling machines have come into existence. They’re called single-bore machines and as the name implies, they’re capable of digging one giant tunnel that could hold both sets of rails and the stations. And if the machine can do so by going deeper underground, it could also minimize construction disruptions at street level by avoiding the hassle of moving utility infrastructure and having to dig [...] stations from the top down.

Under the present timeline, construction to San Jose would begin toward the end of 2020, and the first passenger service would happen come 2026. The full 16-mile plan involves six new stations, from Milpitas to Santa Clara.