キー・システム
The Key System ran special trains to the fair from the East Bay area during the first year, bearing the "X" designation for "Exposition". These trains ran along the same East Bay routes as the Key transbay trains, and used the same rolling stock, the "bridge units", but instead of using the newly opened bridge railway, they were diverted to the old Key System ferry pier ("mole") as there was no stop available at Yerba Buena Island. A ferry crossed the relatively short span of water between the end of the pier and Treasure Island. This service ended at the close of the first phase of the exposition at the end of 1939. In 1940, the "X" train-ferry service was entirely replaced by Key System buses, also designated "X".