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Fri August 23, 2013 - Northeast Edition
Construction of a cable-stayed twin span to replace New York City’s Tappan Zee Bridge between Rockland and Westchester counties is now under way after a delay of more than 10 years.
The replacement bridge was first suggested in 1999. A new span is considered necessary because the existing bridge, built in the 1950s, is used by more than twice the traffic for which it was designed. Approximately 138,000 vehicles now cross daily, resulting in the highest accident rate than on the rest of the New York Thruway. Traffic jams are exacerbated as there is no provision for disabled or emergency vehicles on the current bridge.
In addition, there are concerns about the existing bridge’s structural integrity. The Thruway estimates costs for rehabilitation and maintenance of the bridge will be up to $4 billion over the next two decades, on top of $750 million already laid out for maintenance in the past ten years.
Tappan Zee Constructors (TZC), members of which include Floor Enterprises Inc., Granite Construction Northeast Inc., Traylor Bros Inc., and the American Bridge Company, which built the current Tappan Zee Bridge, is serving as design-build contractor for the job.
It is anticipated the approximately $4 billion project will be completed in 2018, after which the new bridge will not need major repairs for a century. The span will be constructed to the north of the existing Tappan Zee Bridge and will feature eight traffic and four breakdown lanes as well as a lane for commuter buses, a path for pedestrians and bicyclists, and a system for monitoring traffic.
Several nuisance mitigation efforts are included in the design of the new bridge. For example, while pile driving is one of the noisiest phases in construction, TZC will be using vibratory pile driving and drilled shafts as much as possible, along with sound mitigating shrouds, to keep the noise level down. At certain times such as Saturday until midday and all day Sunday no equipment emitting noise above a set level will be used.
In addition, TZC is contractually required to correct activities that rise above certain noise levels and to respond to any such within 30 minutes, with mitigation of the activity within an hour. The public is able to report their concerns about noise and may also monitor noise levels at the bridge’s Web site at www.newnybridge.com.
Other monitoring systems are in place in Westchester and Rockland counties, including vibration and air quality monitoring stations working clock round for the life of the project.
Notice to proceed was issued in January 2013, and by April soil sampling had begun and preconstruction geotechnical work was under way. The test pile program began in July, with permanent pile installation for the main span slated to begin in October.
An unusual requirement for the project was the relocation of thousands of oysters down the Hudson River prior to dredging work, which is expected to involve at least 951,000 cu. yds. (727,091 cu m). Oysters were scooped up by a three-man crew and transferred further south during July. The job took a week and cost approximately $100,000.
Approach substructure work is set for March 2014, with work on the substructure of the main span to follow in June and the erection of the superstructure starting in September of that year.
In December 2016 westbound traffic on the existing span will be moved to the new westbound bridge, followed by eastbound traffic in February 2017. The same month demolition of the current bridge will begin. With completion of both new spans in late 2017, eastbound traffic will then be transferred from the westbound span to the new eastbound bridge in November that year.
The New York State Department of Transportation (NYSDOT) and the New York State Thruway Authority (NYSTA) also are working on the project, and as with the current span the Authority will administer the new bridge.