Valley Transportation Authority's board made it official Friday by voting to press forward with the plan to dig a single large tunnel as it extends Bay Area Rapid Transit to downtown San Jose.

The single-tunnel project has the advantage of being less disruptive to local businesses since the boring will be nearly 100 feet below ground.

But critics said it will end up costing more in the end and worry about how difficult it will be to evacuate riders during an emergency.

The NBC Bay Area Investigative Unit has been reporting on questions surrounding the cost and safety of the design amid a $1 billion federal funding shortfall. Investigative reporter Jaxon Van Derbeken has more in the video above.

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