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Why do many bridges in NY

Adam2
Posts: 1,024
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11/13/2013 7:29:29 PM
Posted: 3 years ago
And many of them were added in the 1960s.
George Washington Bridge -- lower level opened 1962
Verrazano -- lower level opened 1969
SloppyJoe6412
Posts: 24
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11/14/2013 1:03:47 PM
Posted: 3 years ago
With earlier bridge technology (steel structures, suspension cables, no post tensioning) large spans required very deep structures. So it made sense to turn a very deep profile into two driveable surfaces with enough overhead clearance at the lower deck. Both decks could be built at the same time. It could also be split in two for car and train use, although I don;t think it was ever used that way in NYC.

With today's post tensioned concrete bridges, a twin driveable surface makes no economic sense. Decks are more slender. And both decks could not be built at the same time unless the contractor is willing to throw money away.
Adam2
Posts: 1,024
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11/14/2013 8:39:45 PM
Posted: 3 years ago
At 11/14/2013 1:03:47 PM, SloppyJoe6412 wrote:
With earlier bridge technology (steel structures, suspension cables, no post tensioning) large spans required very deep structures. So it made sense to turn a very deep profile into two driveable surfaces with enough overhead clearance at the lower deck. Both decks could be built at the same time. It could also be split in two for car and train use, although I don;t think it was ever used that way in NYC.

With today's post tensioned concrete bridges, a twin driveable surface makes no economic sense. Decks are more slender. And both decks could not be built at the same time unless the contractor is willing to throw money away.

Actually a majority of the bridges in NYC were originally one level, so, probably because of the crowded nature of New York (buildings right next to each other and everything), a second level can alleviate traffic. The question is, why New York?
Adam2
Posts: 1,024
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11/14/2013 8:49:25 PM
Posted: 3 years ago
At 11/14/2013 1:03:47 PM, SloppyJoe6412 wrote:
With earlier bridge technology (steel structures, suspension cables, no post tensioning) large spans required very deep structures. So it made sense to turn a very deep profile into two driveable surfaces with enough overhead clearance at the lower deck. Both decks could be built at the same time. It could also be split in two for car and train use, although I don;t think it was ever used that way in NYC.

With today's post tensioned concrete bridges, a twin driveable surface makes no economic sense. Decks are more slender. And both decks could not be built at the same time unless the contractor is willing to throw money away.

Pardon me why only New York