The SFCTA and SFMTA recently released the Geary/19th Ave Subway & Regional Connections Strategic Case report.

A few interesting takeaways:

* The concept is a \~10-mile rapid transit line from Downtown SF to Daly City via Geary Blvd and 19th Ave.
* Estimated cost is $20–30 billion.
* The study evaluates everything from BART to Muni Metro, but also a standard-gauge regional rail option using high-capacity single-level trains that could potentially integrate with a future Link21 transbay crossing.
* No preferred technology, alignment, or station locations have been selected yet.

The study illustrates two representative concepts. **The first (figure 3-1)** uses BART technology, running directly west from Mission Bay under Geary before continuing south toward Daly City and potentially onward to SFO/Millbrae.  This concept would connect to a future BART-compatible transbay crossing via Mission Bay.  **The second (figure 3-2)** uses standard-gauge regional rail technology, routing via the SF Transit Center and a future Link21 transbay tunnel. The report specifically discusses high-capacity, single-level regional rail vehicles rather than traditional commuter rail equipment (aka Caltrain-type bilevel train sets).

I had previously assumed any future Geary subway would be some form of Muni Metro or automated light rail focused entirely on San Francisco trips. Instead, a significant portion of the report explores how the corridor could be much more impactful if it functioned as part of a broader regional rail network. The standard-gauge concept in particular feels reminiscent of through-running systems such as the Paris RER, London Elizabeth Line, or German S-Bahn.

I've been going back and forth on which concept I prefer. The BART option has the obvious advantage of plugging directly into the existing BART network, allowing one-seat rides from Geary to destinations throughout the East Bay as well as south to SFO and Millbrae. On the other hand, the standard-gauge regional rail concept aligns with several major long-term projects already planned or under construction, including Caltrain's extension to the Salesforce Transit Center, Link21, and eventually California High-Speed Rail reaching downtown San Francisco. That raises the interesting possibility of creating something more like an RER or S-Bahn style regional rail network than a traditional urban subway.

PDF:  
[https://www.sfcta.org/sites/default/files/2026-05/SFCTA\_CAC\_Item12\_Geary-19thSubwayStudyFinalReportENCLOSURE\_2026-05-27.pdf](https://www.sfcta.org/sites/default/files/2026-05/SFCTA_CAC_Item12_Geary-19thSubwayStudyFinalReportENCLOSURE_2026-05-27.pdf)

Geary/19th Ave Subway and Regional Connections Study [San Francisco. May 2026]