Richmond is among the Bay Area locations where BART and Capitol Corridor trains operate in close proximity. Regional transportation planners want to hear from the community about desires for an upgraded an more interconnected regional rail system that will be built by 2040. (Photo courtesy of Link21 Program)

Rail travel across Northern California could see a big shift in the coming decades as rail systems collaborate on a program called Link21.

The program, announced in January by BART and the Capitol Corridor Joint Powers Authority, would include the construction of a second transbay rail tunnel by 2040 and additional rail system improvements across the 21-county Northern California megaregion in an effort to reduce vehicle traffic and make public transit more accessible.

The second rail tunnel will connect Oakland and San Francisco and could eventually serve BART as well as regional rail systems like the Capitol Corridor or Caltrain, said Peter Gertler, Link21 program manager and the senior vice president of the infrastructure firm HNTB.

In Local News Matters’ recent Q&A session on Link21, Gertler and BART’s Acting Link21 Director Sadie Graham laid out how the rail improvement program is taking shape in its still-early development stages.

“A second transbay crossing could be an important solution to reducing congestion throughout the transbay corridor and may also enable expanded BART service hours and other possible system projects,” Gertler said.

The megaregion stretches from Yuba, Sutter and Placer counties to Monterey and San Benito counties from north to south, and from Marin and Sonoma counties along the coast to Stanislaus and Merced counties in the San Joaquin Valley.

The Northern California megaregion is currently home to roughly 12.2 million people but its population is on pace to expand to 16 billion people by 2050, according to a report by the Bay Area Council Economic Institute.

The intention of Link21 and the second transbay crossing is to reduce crowding across the megaregion’s various rail systems while also reducing single-occupancy vehicle traffic and commute times.

While rail transit systems are still reeling from reduced ridership during the COVID-19 pandemic and with the potential for a broad labor shift toward remote work, Gertler argued that ridership has rebounded even after previous events like the SARS pandemic and the Sept. 11, 2001, attacks.

“Our initial market analyses were prepared using pre-Covid data … and we applied various scenarios to test the sensitivity of demand to such things as more remote working and demand moving out of the cities to other areas in the megaregion,” Gertler said. “The initial results indicate that there is sufficient demand even in these cases.”

Graham said Link21 officials are also accounting for potential changes like demographic and workforce shifts as the program continues to gain more momentum.

“The Link21 Program team is definitely looking toward the future, including considerations of demographics, land use and future travel patterns,” she said. “Our team is fully committed to making a passenger rail system accessible and equitable for all people.”

Gertler said Link21 officials have estimated environmental impact reviews for the project beginning between 2024 and 2028, with the intention of formal design and construction beginning during that time as well.

That is, he said, provided that Link21 has the requisite funding to begin building the new rail tunnel.

BART, the Capitol Corridor JPA and the Bay Area’s Metropolitan Transportation Commission have already pooled more than $200 million toward the second transbay crossing’s construction as well as other planned Link21 projects.

While Link21 is still in its early planning stages, MTC has estimated the cost of the new transbay tunnel at up to $29 billion.

Initial study and development funding for the program came from BART’s Measure RR, which voters passed in 2016 and allowed BART to issue $3.5 billion in bonds to support regional infrastructure improvements.

Graham said most options are on the table to fund the program going forward, while Gertler said a program of Link21’s depth will require “a number of different funding sources.”

“The Measure RR funding is augmented by funds from the California State Transportation Agency,” she said. “The Link21 Team is working to identify additional funding sources to carry the project into future phases.”

This month, Link21 officials are expected to hold a handful of webinars to discuss the program’s planned infrastructure improvements, service changes and the results of recent market analysis.

Webinars will be held beginning Nov. 13, according to Link21 officials. Members of the public can also take a survey on the project at

Information on Link21 can be found at