SAN JOSE (KCBS) — BART trains will be running all the way to San Jose by next year.

Transit officials are already planning for phase two of the project, tunneling under downtown San Jose.

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The five miles of BART track from the new Berryessa Station to downtown San Jose will be underground.

The tunnel will be dug by a TBM – a giant tunnel boring machine about 21 feet tall, with a cylindrical cutter head that drills into dirt and solid rock.

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Brandi Childress with the Valley Transportation Authority says while expensive a tunnel is the best option for the downtown core.

“It’s going to not disrupt the businesses on the street level, we’ll have that tunnel like you have that feature like out in Oakland and in San Francisco,” Childress said.

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This stage of the project is expected to cost $4.7 billion, and may require another sales tax measure that could be on the November ballot.