The Southern Pacific's "steam locals" provided the first transbay service from the East Bay to San Francisco. Steam engines chuffed down Adeline in Berkeley to the pier in west West Oakland. Once the Key System was formed in 1903, the Southern Pacific had a hard time competing with the clean and fast trains run by the Key System. To better compete, the Southern Pacific converted its steam local lines to electric lines, which began operation in 1905. People later nicknamed the Southern Pacific's trains the "Red Cars" because of the large red cars (like the one to the left) that were used after the conversion to electric operations.
Southern Pacific Electric trains, along with the Key System and Sacramento Northern, began to operate on the Bay Bridge on January 15, 1939. Due to the bridge operations, the system changed its name to the Interurban Electric Railway (IER). The IER stopped running trains in 1941 along with the Sacramento Northern. Many of the cars from the IER were sent to Los Angeles for service on the Pacific Electric until the early 1960s.