Although plans for a bridge crossing the Hudson River from Westchester County to Rockland County, New York, were developed in the 1920s, the Tappan Zee Bridge did not open to traffic until 1955. New York State's transportation authority decided to make it a toll bridge in 1949.
Although support for the bridge grew with the post-World War II proliferation of freeways throughout the United States, construction of the bridge, known formally as the Governor Malcolm Wilson Tappan Zee toll bridge, began in March of 1952. Work was delayed by two years owing to a steel shortage caused by the Korean War. The engineering firm Madigan-Hyland oversaw construction.
Workers installed eight underwater concrete caissons, essentially large, watertight chambers containing pressurized air, to support roughly 70 percent of the bridge's weight. These caissons are supported by steel pilings attached to bedrock. The design, which was considered innovative at the time, saved the state millions of dollars in construction costs.
Constructed at a natural clay pit about 10 miles north of the bridge site, the caissons were transported to the work site by barge, arriving in October of 1953. Workers floated each caisson to its position before lining them up with steel pipes driven 300 feet below sea level into bedrock.