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 transit, pedestrian, bicycle, and vehicle 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 road users to wait while trains cross.

The Transportation Authority has completed the Pennsylvania Avenue Extension Project Initiation Report (PDF), which developed and evaluated a range of conceptual alignment alternatives. The alignment alternatives reflect different tunnel lengths, configurations and construction methods, with varying implications for existing and potential future station locations along the alignment.

The project was originally recommended by the San Francisco Planning Department’s Railyard Alignment and Benefits Study, which was completed in 2018. The project will be designed to connect to the Downtown Rail Extension, also known as The Portal, 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 Portal led by the Transbay Joint Powers Authority
  • The Southeast Rail Station Study completed by the SF Planning Department
  • The Bayview Station Study led by the Transportation Authority
  • Multi-agency planning and coordination for the 4th and King Railyards
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) and 22nd Street (replacing the current 22nd Street station). The map also shows a potential Bayview Station at either Evans Avenue or Oakdale 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

2020 – 2022: Project Initiation

Development of preliminary technical planning study and preparation of Project Initiation Report

In July 2022, the Transportation Authority Board approved the Pennsylvania Avenue Extension Project Initiation Report, which identified three broad alternatives, based on a preliminary evaluation of constructability, rail operations and interfaces, traffic impacts, utility conflicts, geotechnical and hydrological considerations, cost, schedule, risk, environmental considerations, and benefits.

2023 – 2024: Pre-Environmental Bridging Study

Pre-Environmental Bridging Study to prepare the project technically and organizationally for subsequent environmental review:

  • Refinement and analysis of alternatives
  • Public and stakeholder engagement
  • Implementation approach

Presentation of project pre-environmental report and recommendations for next steps

Future Steps

Environmental review and preliminary design; final design; procurement and construction. The project timeline is subject to funding availability.

Project Partners

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

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

Study Funding

The Transportation Authority Board appropriated $2.5 million in Prop K funds for the Pre-Environmental Bridging Study phase. 

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 Study

Long Alignment

This alternative would provide a tunneled rail alignment (either single bore or twin bores) from the 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 the Downtown Rail Extension to a point immediately north of the existing 22nd Street Caltrain Station. This alignment would require some modifications to the 22nd Street Station, as well as a more complex interface with existing Caltrain tunnels.

Short Alignment

This alternative would provide a “split-tunnel” configuration, with southbound and northbound tunnels separated, with the northbound tunnel within the existing Caltrain right-of-way, and an interface point north of the  22nd Street Station. This alternative would allow for preservation of the existing 22nd Street Caltrain Station, with minor modifications. However, this alternative would have a more significant impact on Caltrain operations during construction.

Station Studies

In 2022, the SF Planning Department completed the Southeast Rail Station Study. The study assessed alternative locations for a station in the Pennsylvania Avenue Extension study area (including the option of retaining the existing 22nd Street Station), as well as sites for a Caltrain Station in the Bayview. The SF Planning Commission endorsed the study and made recommendations for the Bayview and Potrero/Dogpatch/Mission Bay neighborhoods:

  • Advance Bayview station study independent of the Pennsylvania Avenue Extension for restoration of Caltrain services
  • Next phase of Pennsylvania Avenue Extension project development should address station-related considerations within the Pennsylvania Avenue Extension alignment

The Bayview Station Study will finalize the selection of a station location (Evans Avenue or Oakdale Avenue) along the existing Caltrain alignment in the Bayview. The Transportation Authority is currently leading the Bayview Station Study.

The Pennsylvania Avenue Extension Pre-Environmental Study will assess station-related considerations within the potential Pennsylvania Avenue Extension alignment, including with respect to the existing 22nd Street Station.

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.