To address Bay Area traffic, build the tube, skip the bridge

A long-discussed “second crossing” that calls for another car-carrying bridge connecting the east and west sides of the bay has at least one powerful backer: Sen. Dianne Feinstein, who keeps an eagle eye on Bay Area living conditions. But it’s the wrong answer, given scarce money and changing travel needs. Her request for a battle plan on building such a span should be respectfully shelved.

BART’s plan is hazy, written in pencil and sketched in sand. It calls for a second Transbay Tube running to the south of the existing one and hooking up Alameda with several possible spots along San Francisco’s southern waterfront. The Metropolitan Transportation Commission, the regional planning and financing agency, is on the same wavelength with an initial study of six possible routes.

The cost will be eye-popping, beginning at $12 billion with construction overruns or added features nearly a given. The cost of the new eastern span of the Bay Bridge, which doubled, make a bridge just as financially risky.

But a second tube comes with major advantages: It can connect housing and jobs in a way a bridge can’t. The alternatives on BART’s drawing board imagine a transit line up Mission Street — San Francisco’s new financial artery — along with other landing spots in the Mission Bay area, filled with apartments, a medical campus, offices, the Giants ballpark and Warriors arena. There’s thought of linking up with long-dreamed Muni lines running westward across San Francisco.

The tube comes with other draws: It can serve as a backup when maintenance needs and emergencies intrude. Like the existing rail tunnel, it will have two tracks that could be shared with Caltrain and the Capitol Corridor line that runs to Sacramento. Right now, these two services are trapped on either side of the bay with no way to get passengers across without changing seats, stations and tickets, obstacles that push people into their cars. High-speed rail, which has no plans for a direct bay crossing, might tap the new tunnel, too. There’s a significant hitch, though, because BART uses a different track width, a mismatch that should be resolved.

Money remains a huge obstacle. A project of this scale could mean higher fares and tolls along with bond borrowing costs. Federal help will be needed, a longshot in the current atmosphere of tax cuts and private investment in infrastructure projects. Public support will have to be earned with a carefully thought-out blueprint.