Part 2 Analyzing the Transbay Alignments

• BART
• Arrives under the bay at Howard Street in SoMa.
• Runs under Howard Street to 2nd St.
• Turns west to go under O’Farrell Street and on to Geary Street to a terminus to be decided later
• Caltrain/HSR 
• The Downtown Extension DTX follows the Pennsylvania and 7th Street alignment from Potrero Hill to SoMa
• Continues under Townsend St, then turning north under 2nd Street to the Transbay Center
• Continues east out of the Center and on under the bay through a 4-bore 2nd Transbay crossing (2 tracks BART, 2 tracks Caltrain/HSR)
• Muni
• Operates largely as today
• Central Subway extended to North Beach and possibly Fisherman’s Wharf
• Optional extension of N-Judah Mission Bay line further west to Division Street.
• Optional Geary St Muni Metro could loop around Transbay Transit Center and then turn back southwest along Folsom back to the Mission. (not mapped)

Midge’s Delight option. Source: Brian Stokle / Urban Life Signs

Aerial view of SoMa and the Transbay District. Caltrain runs under 2nd St. Muni’s T-Third runs under of 4th St. BART comes from East Bay under Howard St. Transfers possible between all three.  Fremont Transbay Station under Howard has easy transfers to the Transbay Center. 4th & Townsend Station within walking distance of AT&T Park, Chase Center Warriors Arena, and Mission Rock development,. Image: Brian Stokle / Urban Life Signs. Base image: GoogleEarth

The STATIONS

• BART
• Transbay Transit Center at Howard: The station on Howard between Fremont and First streets provides great access to the quickly developing and densifying Transbay District, while still being within walking distance of much of the Financial District north of Market. In addition a short pedestrian tunnel under Fremont would link to the Transbay Transit Center with its Caltrain, HSR, and bus services. The transfer through the tunnel would take less than a minute.

Looking west on Howard Street at Fremont Street. A BART station here would run between Fremont and First and only be a 1 minute walk to the Transbay Transit Center in a pedestrian tunnel. Image: Brian Stokle/Urban Life Signs

• Union Square Powell Station (under O’Farrell Street) provides access to the Union Square shopping and cultural area in addition to providing transfers between the new BART line to the T-Third Muni Metro in the Central Subway, as well as existing Market Street BART and Muni Metro lines. Transfers from the new station could be made by connecting to the concourse under Stockton St. An optional additional pedestrian tunnel could directly link the two BART lines by going under Powell Street between O’Farrell and Market Street. 

The Union Square area already will have the new T-Third station that connects to the Powell St BART and Muni Metro station. Adding the 2nd Transbay BART station under O’Farrell create a major regional rail hub at this important shopping, culture and tourist neighborhood.  Image: Google Maps / Brian Stokle

• Caltrain / HSR
• Fourth and Townsend Station gives access to the same area as the current 4th & King station, with close proximity to AT&T Park, and the planned growth area in the Central SoMa plan. In addition, access to the new Chase Center Warriors Arena would be a short walk away. Transfers to Muni T-Third and the N-Judah would be important.
• Transbay Transit Center: as planned this station will provide rail access into the heart of Downtown San Francisco providing service to the Peninsula, San Jose, as well as Fresno and eventually Los Angeles with the California High Speed Rail. 
• In addition, pedestrian tunnels under Beale Street connecting Embarcadero Station and under Fremont Street to the new BART line under Howard would all connect to the Transbay Transit Center for passengers wishing to transfer from Caltrain and HSR to reach points throughout the Bay Area via BART and Muni.

Transbay Transit Center (center bottum) with its white patterned skin. The Salesforce Tower under construction rises center right with its glass exterior not yet complete.  Image: Brian Stokle / Urban Life Signs

The Cons

• The new BART line does not provide direct access to Mission Bay, which continues to grow with the Mission Rock development, UCSF Mission Bay expansion, and the planned Chase Center Warriors Arena. A transfer from the new line to Caltrain or the Muni T-Third line would be required at:
• Transbay Center Howard (BART to Caltrain) and then Caltrain to 4th & Townsend station.
• Union Square Powell (BART to Muni) and then on Muni to Mission Rock or UCSF Mission Bay station.
• Some of the BART tunnels pass through low lying areas vulnerable to sea level rise of five feet and under. SoMa, east of the Transbay Center where Yerba Buena Cove once existed, is vulnerable to 5 feet of sea level rise. If no mitigations or protections like a sea wall along the Embarcadero are created, the area could experience some flooding in the latter half of the century..
• The DTX tunnel under Seventh and Townsend streets pass through low lying areas susceptible to sea level rise of 4 to 7 feet. The location of the station at Townsend and 4th would be the primary risky location for sea rise unless its station entrances and ventilation shafts were designed to adapt to higher seas and/or a raised ground level.
• Parts of the alignment would require going under private property, especially between Howard St and O’Farrell Street. At a distance of 0.3 miles, this would be technically easy for engineering, but possibly complicated from an easement, building and structural point of view. Luckily, the path does not pass under any tall buildings.
• Tunneling east of the Transbay Center will require removal of some tall buildings (regardless of alignment chosen – which would be very expensive.
• Tunneling east would require breaking through the sea wall due to having insufficient distance to clear below the sea wall.

The Pros

• The new BART line provides direct access to the Financial District with the Howard Transbay Station. With a station inside the neighborhood with the greatest concentration of current BART ridership, and where the highest concentration of employment exists, the Midge option means that passenger demand on the first Transbay Tube (TB1) will likely go down. .
• The BART lines two stations stop at two major transportation hubs:
• Transbay Transit Center
• Union Square / Powell St Station
• The BART line is shorter than other options, and quite straight with only a slight bend, making operations efficient, and making travel times shorter.
• Muni Metro T-Line can be reached via BART at both Powell/Mission and via Caltrain at the 4th & Townsend station.

SF Planning Dept RAB Study looks at possible Downtown Extension alignments. Via Socketsite

Image: Pelli Clark Pelli

Phasing

After the Downtown Extension is built, the four-bore crossing with BART and Caltrain could come next with other San Francisco projects added later.

In Summary