Manhattan Bridge is a suspension bridge spanning 5,780ft across the East River in New York. The bridge connects south-east Manhattan with western Brooklyn. It is the last of three suspension bridges built across the river. The other two bridges are Brooklyn Bridge and the Williamsburg Bridge.
Manhattan Bridge was opened to traffic for the first time in December 1909. The wear and tear of the bridge over decades, especially due to heavy moving loads, has caused maintenance difficulties, which necessitated a long-term reconstruction plan for the bridge.
In 1982, a major reconstruction project for the bridge was initiated by the New York City Department of Transportation. The $834m project was completed in 2007.
Another $149m rehabilitation project, known as Contract No. 14, has been underway since January 2010. Its completion is scheduled for June 2013.
History of the New York-based suspension bridge
Manhattan Bridge is a two-decked suspension bridge running between Flatbush Avenue Extension in Downtown Brooklyn and Canal Street in Chinatown, Manhattan.
The bridge was designed by Leon Moisseiff, who was also engaged in designing the George Washington and Robert F. Kennedy Bridges. Manhattan Bridge’s design was based on deflection theory, an experimental new bridge engineering principle at the time, which advocated relying on the inherent structure of suspension bridges instead of using massive stiffening trusses.
The construction of Manhattan Bridge started in October 1901 and took more than eight years to complete. The bridge was officially inaugurated on 31 December 1909.
The total length of the bridge is 5,780ft from abutment to abutment at the lower level and 6,090ft on the upper roadways, from portal to portal. The main span length of the bridge is 1,470ft. The length of the side spans is 725ft. The length and diameter of each of the four main cables of the bridge are 3,224ft and 21.25in respectively.
Traffic management and need for reconstruction
The bridge carries automobile, truck, subway, bicycle and pedestrian traffic between Manhattan and Brooklyn. It is often used as an alternative to the Brooklyn Bridge, which also connects Manhattan and Brooklyn.
The Manhattan Bridge has three vehicle lanes, four subway tracks, a walkway and a bikeway on its upper level. Four vehicle lanes (two lanes in each direction) are present on the lower level of the bridge.
In total, the Manhattan Bridge allows seven lanes of vehicular traffic, four transit train lines, a pedestrian walkway and a bikeway.
Average traffic flow on the bridge includes 75,000 vehicles, 320,000 transit riders and 3,000 bicyclists and pedestrians. The bridge is also a major truck route.
The reconstruction of Manhattan Bridge was warranted mainly for two reasons. Firstly the bridge, designed and built on deflection theory, had lightly reinforced decks. The foundational design of the bridge was also not found adequate and safe during the long run.
Secondly, the introduction of increasing number of moving loads caused significant strain on the bridge structure. The upper level of the bridge was originally being used for streetcars. But in the 1940s, the streetcar tracks were replaced with auto lanes. The load of transit trains further led to significant twisting strain on the deck.
Cracks and corrosions were found in the Manhattan Bridge structure during an investigation conducted in 1978.
The New York City Department of Transportation (NYCDOT) considered a plan to build a replacement bridge. But finally in 1982, it was decided to rebuild the existing Manhattan Bridge.
Manhattan Bridge renovation work
The $834m reconstruction work on Manhattan Bridge was carried out through a series of contracts. The reconstruction started with two projects ($40m and $97m) to stiffen the side spans and a $350m project to stiffen the main span of the bridge. It was achieved through the installation of a truss stiffening system.
Yonkers Contracting Company carried out the side span stiffening work. Weidlinger Associates oversaw the main span stiffening work.
The project also included the reconstruction of the north and south upper roadways as well as subway tracks, restoration of Manhattan Plaza, construction of a new north bikeway and replacement of the lower roadway.
Manhattan Bridge rehabilitation
The latest rehabilitation project for the Manhattan Bridge has been ongoing since January 2010. The scope of the project includes the replacement of 628 suspenders and the re-wrapping of the main cables of the bridge.
Apart from replacing and upgrading the bridge’s necklace lighting, maintenance platforms are also being built at the towers.
The works are planned in coordination with the simultaneous Brooklyn Bridge Rehabilitation Programme to avoid disruptions.
The rehabilitation project is estimated to cost $149m, which is funded by Federal Highway Administration of New York State and New York City.
Skanska is the main contractor of the rehabilitation project. Other members of the project team are Greenman-Pedersen (resident engineer), Weidlinger Associates (design and construction support) and Sam Schwartz Engineering (community outreach). The project is expected to be completed by June 2013.