キー・システム
The interurban cars had to use a pantograph rather than the trolley pole on Key System rails (electrified at 600 volts) and over the Bay Bridge (electrified at 1,200 volts for the Southern Pacific); the Key System used a covered top-contact third rail over the bridge. Because of the Key System's third rail, cars that could traverse the whole system had to have their third rail shoes removed, since the top-contact shoes would have fouled the Key System rail's cover. They were normally added or removed in Sacramento. Such all-line capable cars were switchable between 600 V and 1,200 V operation; they could also operate at half power at the 1,200 V setting on 600 V overhead.