For years, engineers
thought a bridge could not be built from San Francisco to Oakland because
the water between the two cities was too deep (100 feet at some points)
and too wide. Streetcar lines fed passengers to a fleet of ferry boats crossing
the bay. In 1928, ferries carried over 46 million passengers between the
two shorelines. However, as the automobile increased in popularity, the
need for a bridge became more urgent. Fortunately for the designers, Yerba
Buena Island located between the two shores is a mountain of shale. The
island could be used as an anchorage for two separate bridges.
The crossing from the Oakland shoreline to Yerba Buena Island was an immense
feat of engineering. The 10,176-foot cantilever bridge spanning the space
was the longest bridge of its kind in 1936. The bridge has the world's deepest
bridge pier, sunk 242 feet below the water level.
The East Bay cantilever bridge and the suspension bridge from San Francisco
meet at Yerba Buena Island via a tunnel through the shale hill on the island.
The largest diameter bore tunnel in the world, the Yerba Buena Tunnel measures
76 meet wide, by 56 feet high.
Almost as soon as the Bay Bridge was opened in 1936, traffic exceeded levels
predicted for 1950. Traffic continued to increase and in 1958, $49 million
was allocated to re-configure the bridge. The railway system was removed
and the upper deck was realigned to carry five lanes of westbound truck
and auto traffic. The lower deck carried five lanes of eastbound traffic.
Increasing traffic volumes led to creating HOV lanes in 1971, and by 1973
more than half of the 50,000 commuters using the bridge during morning rush
hour were using the HOV lanes. Installation of a signal system to regulate
traffic on the bridge also helped with congestion, allowing as many as 500
more vehicles per hour to cross the bridge during peak periods.
In 1989, a section of the East Span of the Bay Bridge was damaged in the
Loma Prieta earthquake. Bolts holding a section of the upper deck on the
truss section sheared, causing a portion of the deck to unhinge and fall
onto the lower deck. Interim retrofit work to prevent any future failures
has begun on the East Span until the new bridge can be built. The West Span
of the bridge will be retrofitted, but not replaced. |
