8: Yerba Buena Island Tunnel Background: Yerba Buena Island is a
small chunk of land resting in the San Francisco Bay, between
Oakland and San Francisco. A cantilevered bridge flanks this
five-lane tunnel on one side, with a double suspension bridge on
the other. Why It's Unique: With a 76-foot diameter, Yerba Buena
Island Tunnel is the world's widest single-bore tunnel, an
impressive feat considering it opened in November of 1936.
Hashash speculates that adding the tunnel was the most cost-
effective solution to allowing a passage through the island, as
opposed to just building one enormous bridge.