The Northway’s Twin Bridges, the Capital Region’s busiest interstate highway bridges, will be getting new suspension cables.
The 168 thin steel cables are a key structural component of the bridges, which separately carry the northbound and southbound lanes of Interstate 87.
The cables bear the weight of the deck below the arch of each bridge. They will be replaced over the next 14 months in a major repair to the nearly 50-year-old bridges.
Contractor Piasecki Steel Construction Corp. of Castleton has already begun work on the $11.9 million project, which is expected to last until November 2009. Federal transportation money is paying most of the cost.
The 2-inch-diameter cables run vertically along the length of each bridge, holding and distributing the weight of the deck. After 50 years of use, they are showing signs of fraying and rust.
The work will extend the life of the bridges, known officially and collectively as the Thaddeus Kosciusko Bridge.
“The replacement cost of these bridges in today’s dollars would be $42 million,” said Brian O. Rowback, the state Department of Transportation’s Region One director. “This work will extend the useful life of the bridges for decades.”
Officials explained the project at a press conference Thursday in the shadow of the bridges’ Saratoga County abutments. The pair of bridges span the Mohawk River between Halfmoon in Saratoga County and Colonie in Albany County.
The bridges carry 110,000 vehicles a day, making them the region’s busiest bridges — far more even than the Patroon Island bridge across the Hudson River at Albany, which carries 85,000 vehicles daily.
The bridges, in addition to seeing daily commuter traffic, are on a major freight truck route between Quebec and United States cities and are also vital in tourism and emergency services transportation.
“The Twin Bridges continue to play an integral role in the overall transportation system and economic well-being of the Capital District and New York state,” Rowback said.
The two massive steel arches are connected to the bridge decks by the steel cables that distribute the decks’ weight. The contractor has come up with a plan that will let them be replaced without major disruptions to traffic.
The bridge will remain in use throughout the work, but officials urged motorists to cooperate.
Emmitt McDevitt, a Federal Highway Administration safety engineer, said drivers will need to keep their eyes on the road despite what will be the distracting appearance of men working in the air above.
“We’re going to need the cooperation of each and every commuter,” McDevitt said. “People need to avoid the temptation to gawk, maintain their speed and keep their eyes on the road.”
There will be some single-lane closures, but Rowback said they will be during off-peak hours. Work is expected to be continuous between now and November 2009, weather permitting.
The Twin Bridges are 779 feet long. At their maximum height, the arches are 100 feet above the driving surface.
The cables are of varying length, but Rowback said the biggest of the cables is 92 feet long and weighs 800 pounds.
The Twin Bridges are inspected every other year, most recently in December 2006. The structure was given a rating of 4.1 on a scale of 1 to 7.
“It’s in pretty good shape for a 50-year-old bridge, but it needs maintenance,” DOT spokesman Peter Van Keuren said.
During preparation for the cable replacement, Rowback said test cores were drilled in the bridge deck and the deck itself was found to be in good shape.
McDevitt said there will be a lot more maintenance and repair projects on the interstate highway system in the next few years as major components reach the half-century mark and face age-related deterioration.