I feel like talking about the amazing interurbans that existed in around the San Francisco bay area, and that have been fascinating me lately: The famous Key System (spiritual forerunner to BART), the Southern Pacific's East Bay Electric Lines (later renamed Interurban Electric Railway), and the most wonderous one of all, the Sacramento Northern.
In the early years of the 20th century, before the Bay Bridge, those lines would connect to ferry services to San Francisco. With the opening of the Bay Bridge they would reach the Transbay Terminal using the tracks on the lower level of the bridge. This arrangement would last less than 20 years, from 1939 when the bridge railway was opened, to 1958 when the Key System was abandoned. The East Bay Electrics, renamed in 1938 to Interurban Electric Railway, would cease passenger service in 1941, as would the Sacramento Northern. The Key System then extended some of their lines using abandoned IER tracks.
Pic related shows the situation in 1927, at its pre-bay bridge heyday. It shows the Key System, the East Bay Electrics, and, though not marked in the legend but visible on the map, the Sacramento Northern. Here you can see a yuge hq version:
https://commons.wikimedia.org/wiki/Category:Key_System#/media/File:1927_East_Bay_Electric_Lines_and_Key_System_map.jpg 