On May 24, 1883, the Brooklyn Bridge opened to the public, revolutionizing bridge construction and transportation in the United States. John Roebling and his son Washington had connected New York and Brooklyn, the nation’s first and third largest cities, using the new suspension bridge technology and spinning of steel cables. In the late 19th and early 20th centuries, new bridges utilizing suspension cables, cantilevers and arches made it possible to conquer previously unspannable distances.
While bridge technology incorporated more concrete and steel, engineers gained a greater understanding of the fundamentals of physics, and bridges of a longer span, like the Verrazano-Narrows Bridge. In the post-World War II era, these bridges helped connect highways through the Interstate Highway System that began in 1956. One such structure, the Tappan Zee Bridge, spans the Hudson River between Tarrytown and Nyack, NY, north of New York City at its second greatest width (to avoid the jurisdiction of the Port Authority of New York and New Jersey), and is a key connection of the New York State Thruway, which stretches from New York City to Buffalo.
However, the Tappan Zee Bridge was not built to last . Unable to reach the bedrock 300 to 800 feet below sea level, the engineers designed its foundation to float above bedrock. Like many other post-World War II bridges, it was built to be “non-redundant,” based on a belief that computer technology made redundancies unnecessary. This means that a loss of structural integrity in any load-bearing member could lead to bridge collapse because the weight or load in that area can’t be transferred and supported by another section. Designed to carry 100,000 vehicles per day, it now averages 140,000 and has peaked at 170,000. The New York State Thruway Authority is currently developing a plan for a new bridge and a debate is taking place whether to include rail and/or bus rapid transit on it.
Building on the success of the High Line in New York City and the Walkway-Over- The-Hudson, which reuses an abandoned railway bridge in Poughkeepsie, the Tappan Bridge Park Alliance has begun a campaign to turn the existing structure into a park and pedestrian/bicycle path. While the Thruway Authority proposes its demolition, the Alliance hopes to create a large recreational park and transportation alternative beyond the automobile (sketch of proposed redevelopment below right).