<P> The site of the bridge, at the Hudson River's second - widest point, added to construction costs . The site was chosen to be as close as possible to New York City, while staying out of the 25 - mile (40 km) range of the Port Authority's influence, thus ensuring that revenue from collected tolls would go to the newly created New York State Thruway Authority, and not the Port Authority . A unique aspect of the design of the bridge is that the main span is supported by eight hollow concrete caissons . Their buoyancy supports some of the loads and helps reduce costs . </P> <P> The bridge was designed by Emil Praeger of the Madigan - Hyland engineering firm . Captain Praeger helped develop floating caissons during World War II when the Allied forces needed to create and protect portable harbors for the 1944 invasion of Normandy . </P> <P> Construction started in March 1952 and the bridge opened to traffic on December 15, 1955, along with a 27 - mile (43 km) long section of the New York State Thruway from Suffern to Yonkers . New York State Governor W. Averell Harriman signed a bill on February 28, 1956, to officially name the structure the Tappan Zee Bridge . In 1994, the name of Malcolm Wilson was added to the bridge's name upon the 20th anniversary of his leaving the governor's office in December 1974, though it is almost never used when the bridge is spoken about colloquially . </P> <P> The bridge is expected to be decommissioned in October 2017 . </P>

When was the old tappan zee bridge built