The Key System (so named because its route formed the shape of a skeleton key), served the East Bay area with service from Oakland and other cities into San Francisco. Originally, the cars ran to a ferry terminal, but with the construction of the Oakland Bay bridge, service was direct to a terminal in San Francisco (the SP, Key System and Sacramento Northern were on the lower deck of the Bay Bridge).
Eventually the auto took over and the system was dismantled, only to be resurrected years later by the Bay Area Rapid Transit (BART) system.