It’ll be a monster project — a second transbay rail line tunneling under submerged muck, or bridging over Yerba Buena Island. It’ll cost untold billions and consume incredible amounts of labor and materials. And while it won’t be realized for at least several decades, the first serious discussions about how to build a second crossing are underway.“There’s a lot of interest in this because it could change the urban fabric of the Bay Area,” said Matt Maloney, the principal of major projects for the Metropolitan Transportation Commission. MTC has been co-leading early talks among regional-transit agencies about the technical feasibility of a second crossing.Their finding: It’s possible.And the Bay Area Council and the urban planning think tank SPUR have both released reports underlining the desirability of a second crossing.But because it would profoundly reshape the Bay’s social geography, many are insisting these discussions focus on economic and racial justice from the start.The Bay Area’s previous mega-projects, such as BART’s Transbay Tube and the federal highway systems, delivered access to top jobs, good schools, and healthy neighborhoods for predominantly white, affluent suburbanites. But for communities in the urban core, like Black West Oakland, these were wrecking balls bypassing them on the path to prosperity.“We already can assume a mega-project will have a negative impact on certain communities,” said Clarrissa Cabansagan of the transportation policy group TransForm. She pointed to even more recent projects, like the Oakland Airport Connector, as an example of a poorly planned and executed transit expansion. “Let’s make sure we don’t make the same mistakes of the OAC that just flew past East Oakland,” Cabansagan said.Transportation agency officials say they want to avoid repeating history. “There’s an acknowledgement of what’s happened in the past with BART, what kind of an impact that had,” said BART board president Rebecca Saltzman. An “equity lens,” she insisted, is necessary at every stage of planning for new BART infrastructure.In fact, Saltzman said this goes so far as to accept that a new BART tube isn’t necessarily the long-term answer. Instead, the best option might be spanning the Bay with CalTrain, high speed rail, or Amtrak.“It’s important not to presuppose and get stuck on one thing,” Saltzman said. “The Bay has done that in the past, and it hasn’t worked out well.”Whatever form a second crossing takes, groups like TransForm want to make sure it doesn’t fuel displacement of low-income households, or disinvestment in the transit infrastructure many currently rely on.TransForm recently released a report recommending steps to ensure a second transbay crossing doesn’t do harm. Their top recommendation: Fix the systems we already have, buy new BART cars and controls to speed up services, and run more transbay buses.BART director Robert Raburn said his agency is already following this principal with Measure RR, the $3.5 billion bond approved by voters last fall. It’ll be spent fixing the system’s existing routes and stations, and BART’s new cars and controls will increase capacity in the existing transbay tube.Matt Nichols, the policy director for infrastructure and transportation for Oakland Mayor Libby Schaaf, agrees that a new crossing shouldn’t divert resources away from existing services. But he said a second crossing would help low-wage workers who commute across Bay.“It hurts graveyard shift workers that BART doesn’t run all night,” Nichols said. “And if it goes down, you don’t have any resilience, because people can’t get to their jobs. Poor people pay a disproportionate price if they’re late to work and are more likely to get fired if they don’t show up.”Of course, a second crossing would also boost land values around new stations. Developers will clamor for the land. For example, a new ballpark could be built atop a BART station in the Jack London District. Or, Interstate 980 could become a parkway lined with thousands of new homes, served by multiple underground stations with lines heading into San Francisco. But rising rents would push out many existing residents.“The speed of displacement is out of control,” Nichols said about Oakland’s current boom and housing crisis, but he added that a new BART line down the 980 could help repurpose the land and create new housing that would ease the shortage.Raburn said BART’s 35 percent affordable-housing requirement around its stations is one policy that will mitigate potential displacement.But Cabansagan said cities like Oakland need to do more — especially around transit stations. “The reality is the communities that need transit the most are being displaced right now, and transportation improvements are often exacerbating their ability to stay,” she said.