Staff working on Link21, a project to build a second underground rail link between San Francisco and Oakland, recently recommended building a connection for standard gauge trains, rather than for broad gauge BART trains.

The staff’s primary rationale is that a standard gauge tunnel would better connect various regional, intercity, and future high-speed rail services in Northern California, as all except BART operate on standard gauge tracks. The standard gauge tunnel would accommodate multiple operators, similar to the rail infrastructures in New York and other northeastern cities, serving Amtrak and numerous regional rail agencies. In the urban core, current lines with less frequent intercity service could be enhanced by adding frequent metro service to Downtown San Francisco. Additionally, the standard gauge tunnel aligns better with the upcoming State Rail Plan, which calls for more high-capacity interregional passenger service.

I believe the recommendation is sound. Considering the funding, planning, and construction difficulties in recent decades, I think it’s important for a rail vision like Link21 to break down into smaller components with independent utility to have the best chance of being implemented. For over four decades, transit activists on the San Francisco Peninsula have advocated for an electrified Caltrain serving downtown San Francisco. While the vision is yet to be fully realized, many components, such as electrification, are complete.

With the standard gauge concept, this project would extend Caltrain from the planned terminal at Salesforce Transit Center to the East Bay. Another project already covers the rail extension from the current 4th & King to Salesforce Transit Center, with much of the environmental planning work done. A completed station in downtown San Francisco would make the new transbay rail tunnel less costly and complicated. Trains from the East Bay could continue through San Francisco and down the Peninsula without additional lines.

With a broad gauge link, new subways and tunnels would be necessary in San Francisco. Although many people desire a subway down Geary Boulevard (as originally envisioned in the 1950s when the city removed the still productive B-Geary surface streetcars), that is a mega project on its own and unlikely to be built before or concurrently with the second crossing. I believe this is the biggest disadvantage with going broad gauge. With or without the Geary subway, there’s still the issue of a train storage or maintenance facility on the west side of the Bay. When BART originally opened in 1974 in San Francisco, it lacked a train storage or maintenance facility on the San Francisco Peninsula, which hampered service frequency and reliability.

In the East Bay, a key benefit of a broad gauge crossing is that existing BART branches have the capacity for increased service. However, simply adding more service to current stops does not expand the “transit-shed” in the East Bay and may actually increase parking and car traffic strain, which was already high pre-COVID, at those stops. In contrast, under the standard gauge scenario, additional tracks and possibly electrification would be necessary in the East Bay on existing standard gauge passenger lines. These parallel lines, such as the Coast Line planned under the South Bay Connect project, are located far enough from existing BART lines to provide a new “transit-shed” without adding pressure to existing BART stops.

Some argued that a broad gauge is better for the second crossing because it can support new urban metro (BART) lines in San Francisco and the East Bay. However, I believe a standard gauge crossing is equally suitable for supporting new metro lines. In an ideal scenario, with funding and strong political support, new subway lines down Geary in San Francisco or MacArthur in Oakland could be built with standard gauge and 25kV overhead electrification, using the second rail crossing. BART could even build and operate these lines, like it does with eBART. There are many examples of urban metro lines powered by 25kV overhead wires in Asia. Even in the United States, Denver RTD runs metro-style electrified classic FRA-compliant trains between the Denver Airport and downtown every 15 minutes.

Thinking even long term, a standard gauge crossing and subway could facilitate a rail connection to the North Bay—something the original BART planners envisioned but never delivered. The North Bay has the standard gauge SMART serving as its rail backbone that could be extended to San Francisco.

For a modest initial project of just building a second link from Salesforce Transit Center to Oakland, a well-located station in Oakland can ensure success of the second tunnel by facilitating easy transfers between Caltrain and BART. There’s a concept of converting the I-980 freeway into a surface boulevard and using the underground space for a new rail station. Broad gauge BART would have new tunnels to serve this station, not only to connect with Caltrain but also to provide additional track capacity in Oakland for more service on the outer branches, though without crossing the Bay. The I-980 space can also provide storage for Caltrain in the East Bay. Additional track improvements needed to extend metro service further into the East Bay can be implemented separately.

While the concept of a standard gauge second crossing doesn’t address whether transit agencies should merge, it doesn’t rule it out. In many ways, a merger of BART and Caltrain could offer significant benefits, such as better service coordination, simpler fares, seamless transfers, and a unified regional identity.

Considering the upcoming political environment, the second rail crossing is still decades away. Even the project to extend Caltrain from 4th & King to Salesforce Transit Center is at risk. Proposing to build the tunnel with standard gauge should improve the project’s position with the state and future federal government. The California State Transportation Agency (CalSTA), a cabinet-level agency overseeing departments like the DMV, Caltrans, and the High-Speed Rail Authority, is already interested in taking a leadership role in this project due to its statewide significance. Although it seems like a long shot, by planning now, cities can coordinate land use and secure future right of ways by ensuring no major structures are built that would block the tunnel.