Originally divided into three
lanes in each direction, the upper deck of the Bay Bridge was designed
for automobiles and other light vehicles. Trucks and buses used three lanes
on the lower level of the bridge, sharing it with the Key System and Interurban
Electric (Southern Pacific), which operated trains using two standard gauge
electric railway tracks, separated from vehicular traffic. Ten-car trains
ran directly from Alameda, Berkeley and Oakland to the newly constructed
terminal in San Francisco. The trains were scheduled to run as closely
as 63 seconds apart in order to handle the passenger load. The first year
of bridge traffic was estimated to be approximately 6 million vehicles.
This number would gradually increase until it reached 9 million by 1950.
However, the bridge actually carried 9 million vehicles the first year.
The train tracks were removed from the Bay Bridge, and the bridge decks
were converted to their present traffic configuration, during a 4-year
project begun in 1958 (at a cost of $35 million), after the Key System
abandoned transbay service due to decreased patronage.