Caltrain train at a railroad crossing

Photo by SFMTA Photography Department


The Pennsylvania Avenue Extension project will support future uninterrupted passenger rail service through San Francisco. The project will place current Caltrain and future California High-Speed Rail passenger rail lines underground, allowing vehicle, pedestrian, and bicycle traffic to flow uninterrupted and improve safety for all road users. 

The Transportation Authority is studying potential tunnel alignments that will have trains running underground along Seventh Street and Pennsylvania Avenue, in order to remove existing Caltrain rail crossings at Mission Bay Drive and 16th Street and eliminate the need for traffic to wait while trains cross. 

The project, as recommended by the SF Planning Department’s Railyard Alignment and Benefits Study, will be designed to connect to the Downtown Rail Extension, which will bring Caltrain and California High-Speed Rail from 4th and King streets to the Salesforce Transit Center.

The Transportation Authority is closely coordinating the Pennsylvania Avenue Extension work with related initiatives, including the Downtown Rail Extension led by the Transbay Joint Powers Authority, the Southeast Rail Station Study led by the SF Planning Department, and multi-agency planning and coordination for the 4th and King Railyard.

Map showing the Pennsylvania Avenue Extension project area from Cesar Chavez to the DTX/PAX Interface at the current Caltrain yard. The DTX project area continues North along Townsend to 2nd Street and the Salesforce Transit Center. Potential future stations are shown at 4th & Townsend (replacing the current 4th & King station), Mariposa Street, Cesar Chavez, Evans Avenue, Oakdale Avenue, and Williams Avenue.

Project Goals

Increase connectivity between Mission Bay, Potrero Hill, and Design District/SOMA neighborhoods

Improve safety of pedestrian, bicycle, and vehicle traffic on surface streets

Enable improved efficiency of Caltrain operations and service planning

Improve quality of life in surrounding neighborhoods by substantially reducing existing congestion and air quality and noise effects associated with existing Caltrain and future rail expansion

Timeline and Status

Summer 2020 to Fall 2021 
Development of preliminary technical planning study and preparation of project initiation report

Refinement of alignment alternatives

Preliminary evaluation of constructability, rail operations and interfaces, traffic impacts, utility conflicts, geotechnical and hydrological considerations, cost, schedule, risk, environmental considerations and benefits for feasible alignments

Fall 2021 to Winter 2022
Preliminary public and stakeholder engagement

Presentation of project initiation report and recommendations for next steps

Future Steps (approximately 10 or more years for further project planning, design, and construction) 
Further pre-environmental technical analysis; environmental review and preliminary design; final design; procurement and construction

Project Partners

The Transportation Authority is leading the conceptual design study work for the Pennsylvania Avenue Extension in close coordination with

  • Caltrain/Peninsula Corridor Joint Powers Board
  • Transbay Joint Power Authority
  • City and County of San Francisco
  • SF Planning Department
  • California High-Speed Rail Authority
  • San Francisco Public Utilities Commission
  • Caltrans

Cost and Funding

The Transportation Authority Board appropriated $1.6 million in half-cent transportation sales tax funds for the current conceptual design study of the project. 

Funding for construction will be identified in later phases of work. 


Downtown Rail Extension
Southeast Rail Station Study (SF Planning)


Jesse Koehler, Rail Program Manager

Key features

Pennsylvania Avenue Extension Tunnel Alternatives Under Consideration

Long Alignment
This alternative would provide a tunneled rail alignment (either single bore or twin bores) from Downtown Rail Extension to a point immediately north of Cesar Chavez Street. This long alternative requires replacement of the existing 22nd Street Caltrain Station.

Mid-Length Alignment
This alternative would provide a tunneled rail alignment (either single bore or twin bores) from Downtown Rail Extension to approximately the site of the existing 22nd Street Caltrain Station. This alignment would require some modifications to the 22nd Street Station.

Short Alignment
This alignment would allow for preservation of the existing 22nd Street Caltrain Station, with minor modifications.

The SF Planning Department’s Southeast Rail Station Study is assessing alternative locations for a station in the PAX study area (including the option of retaining the existing 22nd Street Station), as well as sites for a Caltrain Station in the Bayview. The Pennsylvania Avenue Extension may require modification or replacement of the 22nd Street Station, depending on the alternative. The Pennsylvania Avenue Extension concept design work is being coordinated with the development of the Southeast Rail Station Study.

Related programs


The Downtown Extension is a plan to extend Caltrain and future California High-Speed Rail service from 4th and King rail yard to the newly-constructed Salesforce Transit Center.

The Caltrain Electrification project will bring fully electrified service to Caltrain.