Manhattan Bridge’s secrets (and not only)

The third bridge over the East River by now is an iconic example of the evolution of engineering techniques

The Manhattan Bridge has always been overshadowed by its legendary brother further south, the Brooklyn Bridge. Even today, some consider it “only” the third in a series, as it is a blend of design between the Brooklyn and Williamsburg Bridges, built on the East River 26 and six years earlier, respectively. Tourists flocking to New York head towards the breathtaking walkway of the Brooklyn Bridge, one of the most famous bridges in the world, overlooking the Manhattan Bridge, even though it offers more or less the same view since the two are very close.

It was opened at the end of 1909 and even during the design phase, it was called Bridge Number 3, a name later changed to the Manhattan Bridge, a choice that became official despite opposition from The New York Times, which advocated for a less generic name, suggesting Wallabout Bridge due to its proximity to Wallabout Bay in Brooklyn. The Manhattan Bridge, under political pressure, also saw changes in its structural designs and designers. The bridge, located at Canal Street in Lower Manhattan, and connecting to Brooklyn at the extension of Flatbush Avenue, gained notoriety with the movie poster of Sergio Leone‘s “Once Upon a Time in America,” starring Robert De Niro, featuring an iconic photo. Some mistake that glimpse of the bridge in the fog and vapors of New York for the Brooklyn Bridge, but it is actually the Manhattan Bridge.

At the school of engineering on the bridges of the East River

The trio of bridges over the East River is an important element in the architecture and engineering school of the 20th century, particularly in the history of suspended bridge construction. Starting from these New York infrastructures, progress has been made, from the George Washington Bridge in New York to the Golden Gate Bridge in San Francisco, to the modern era and today, with the Japanese bridge over the Akashi Strait and the one in Italy over the Strait of Messina, which, once built, will break the record for the longest suspended bridge in the world, the Cannakale Bridge in Turkey.

The construction of the Manhattan Bridge began in 1901 and was completed eight years later because the construction of suspension bridges had become more standardized and much faster than in the previous century when it took 13 years to build the Brooklyn Bridge. The bridge has two levels with a total length of 5,790 feet (1,765 meters) in the lower deck and 6,090 feet (1,856 meters) in the upper deck, while the central suspended span is 1,470 feet (448 meters) long.

What gives the Manhattan Bridge the satisfaction of a record is the design technique that, for the first time in the world, was based on the theory of deflection, introduced in 1888 by the Austrian Josef Melan. According to this theory, the deck and cables flex together to bear the loads. This allowed for the lengthening of the suspended structure, reducing the required rigidity of the deck.

Deflection theory particularly influenced the design in the 1930s, when with increased span spans the ratio of deck height to span length was reduced to achieve a lighter, more graceful appearance without compromise security. Even the towers benefited from these innovations introduced in those years, starting with the Manhattan Bridge.

Compared to the massive structure of the Brooklyn Bridge, and to a lesser extent, the Williamsburg Bridge, the Manhattan Bridge features two slender fixed steel towers that extend laterally at the base, with a much lighter and less deep stiffening truss, thereby reducing the amount of materials needed for construction.

The subway runs on the bridge.

Since its inception, the bridge has accommodated subway service, with trains starting to operate in 1915. The twin roadways above the subway tracks were added in 1922 as a tram right-of-way, only to be replaced by automobiles in 1929, which were becoming a popular mode of mass transportation, despite carts and horse-drawn carriages continuing to cross it for many years. The Manhattan Bridge underwent significant upgrades and repairs over the decades, first in 1940 and then again for a decade starting in 1990 when subways had to be rerouted through tunnels. Pedestrian and cycling paths on the North and South sides of the bridge, respectively, which had been removed in the mid-1960s, were also renovated.

The bridge now has seven lanes for vehicle traffic, four transit rail lines, a pedestrian walkway, and a separate bicycle path. In 2009, the centennial year of the bridge, the American Society of Civil Engineers (ASCE) designated it as a National Historic Civil Engineering Landmark. According to data from the Department of Transportation (NYC DOT), the bridge sees an average daily passage of over 75,800 vehicles, 6,200 cyclists, and 2,700 pedestrians. The Brooklyn Bridge records a passage of 116,000 vehicles, 3,000 cyclists, and over 30,000 pedestrians.