Caltrain connects San Francisco to the Peninsula, Silicon Valley and San Jose. Caltrain's full potential is not realized because it does not directly serve downtown San Francisco.

Extending Caltrain 1.3 miles underground into the proposed rebuilt Transbay Terminal will provide fast access to the heart of downtown San Francisco and create a convenient central transit hub under one roof. It will enable riders to transfer directly between Caltrain, AC Transit, BART, Golden Gate Transit, and SF Muni to all parts of the city, as well as future high speed rail to the Central Valley and Southern California. The Transbay Terminal project will greatly increase transit ridership because it will eliminate time-consuming extra transfers between transit carriers.

The two main components of this project are the actual subway extension of Caltrain tracks along 2nd street, and construction of a completely new Transbay Terminal with the rail terminal at its basement level.

The battle over the 80 Natoma property in the path of the proposed rail tunnel stalled the project during 2004 and 2005. The following article gives an excellent overview of this issue:

• Tower Inferno: Mayor Newsom aids a developer at the apparent expense of the Transbay Terminal, SF Weekly, Wednesday, June 16, 2004
  
  
• Compilation of news articles, 2004-2005...
• Updates and alert announcements, June 2004 through March 2006,
  in reverse chronological order...