I used work summers in San Francisco and remember the big Amtrak sign at the old Transbay (bus) terminal. For some reason I used to think there were tracks underground but later realized it was used for connecting buses. I think they had services there.
I wonder if the plans are for Amtrsk to return there once the new Transbay Terminal is ready.
Besides the MUNI streetcar tracks in the front 'driveway' of the old terminal, originally there were tracks along the upper level bus platforms last used by A C Transit and Greyhound. These were for the old interurban electric trains that crossed the Bay Bridge.
Amtrak thruway buses loaded at street level at the rear of the terminal. At one time Continental Trailways buses also loaded at the street level on the side.