SF - Oakland Bay Bridge
The Golden Gate's eastern cousin, the San Francisco-Oakland Bay Bridge, holds the title of longest high-level bridge in the world at 8.4 miles. Completed in 1936, the Bay Bridge earned the honor of being declared the seventh wonder of the world in 1955 by the American Society of Civil Engineers. It is actually two different types of bridges--suspension on the San Francisco side and cantilever on the Oakland side connected via tunnel through Yerba Buena Island.
Due to the extraordinary depth of the water, ranging from 50 to 105 feet, and a bay floor thick with several layers of mud, the building of the bridge brought about new engineering challenges.
Special caissons, watertight chambers, were designed for digging through the Bay floor in order to embed the bridge's foundation in bedrock. As more people began making the East Bay their home, the Bay Bridge became the most heavily traveled bridge in the Bay Area, third busiest in the country, carrying more than 250,000 vehicles daily.