The idea of a bridge across the Hudson as part of a highway system that would encircle the New York-New Jersey metropolitan area had been around for a while. Delayed by the years of the Great Depression and the Second World War, serious discussion began in 1949 when the New York State Thruway Authority (NYSTA) planned to build a toll superhighway that would connect all the major cities of New York State, and would include crossing the Hudson River.
The first plans were too close to New York City (the Port Authority has jurisdiction over a 25-mile radius) and so the proposal was moved north to the Tarrytown-Nyack crossing. Although the river is very wide at this point, the plan was approved in 1951 and construction began in March 1952. The bridge was a cantilever and truss design, with the main cantilever span 1,212 feet in length, comprised of cantilever spans of 340 feet and a suspended span of 531 feet across the main channel of the river. The central cantilever span was supported by eight underwater concrete caissons (watertight structures). These caissons were hollow with air stored in various compartments. Water was periodically pumped out to achieve the desired buoyancy. This design helped to reduce costs and also to support greater loads on the bridge.
The original Tappan Zee Bridge opened to traffic on December 15, 1955, replacing the Tarrytown-Nyack ferry.
A unique feature of this bridge was the movable concrete barrier that changed the direction of traffic for the afternoon rush hour in the central (7th) lane. The changeover took about 45 minutes and involved 2 barrier moving machines working together.
Since this bridge was so long it was quite an amazing experience to drive across, with the approach section close to the surface of the wide Hudson River. In good weather it was common to see a variety of watercraft on the river, and even the skyline of New York City might be visible in the distance.