Wednesday marked the unveiling of a new multiyear planning process by BART and regional rail providers to expand, integrate, and improve rail service across the Northern California "megaregion" — and a key component of the plan will be a second Bay crossing for BART between San Francisco and Oakland.

The plan, dubbed Link21, calls for a Phase 1 process that will establish a "preliminary business case" for greater integration of rail service across a 21-county region — which includes the Sacramento area, the northern San Joaquin Valley, and the Monterey region. And that will be followed by the creation of a "preferred program alternative" that will then make way for a project selection process that's set to begin in three years. And a central project — potentially the most expensive — in the plan will be a second Transbay Tube or similar type of Bay crossing for the BART system.

"Link21 will help shape Northern California’s rail system for future generations,” said Rob Padgette, managing director of the Capitol Corridor, in a statement Wednesday. "This program will dramatically improve how our riders get to and from the San Francisco Bay Area."

And BART spokesperson Alicia Trost tells the Chronicle, "We can’t lose sight of what’s needed to serve future riders and we cannot allow the pandemic to slow this down. That would be at the detriment of future riders, current riders and those that are making housing and job decisions."

Talk about a second Transbay Tube goes back a decade or more, and in 2014, BART began officially studying the idea, with an initial concept being a tunnel that would connect Alameda and SoMa, and perhaps extend to parts of San Francisco still under-served by transit, like the Richmond District. In 2019, an East Bay transit planner and SPUR board member publicly suggested "why not three crossings?", adding in a proposed aerial bridge across the Bay connecting Millbrae with Bayfair Station. And while we're at it, why not a rail connection between Marin County and San Francisco, or Marin County and Contra Costa County?

These are perhaps ideas that will be batted around further and brought into logistical focus in the Link21 planning process. But most importantly, this means that a second train connection between the San Francisco Peninsula and the East Bay is becoming more than pie-in-the-sky talk.

As the Chronicle notes, BART has already put $110 million toward project planning from its Measure RR bond, which passed in 2016. And additionally, the Metropolitan Transportation Commission (MTC) has put $210 million toward project planning, and BART approved a $50 million contract two years ago with infrastructure design firm HNTB Corporation for "advising and program management services" for the second tube crossing. The whole project, according to best current estimates, may cost $29 billion.

Meanwhile, the MTC and the Association of Bay Area Governments have been working on Plan Bay Area 2050, which focuses on long-range plans for just the nine-county Bay Area in the realms of the economy, the environment, housing and transportation. That effort is expected to produce a final "blueprint" document by Fall 2021.

Previously: Second BART Tunnel? Hell, Let’s Add a Third Bay Crossing, Says East Bay Planner

Photo: Giorgio Trovato