Construction will begin this spring on the largest transportation design/build project to date in the United States, New York State’s replacement for the Tappan Zee Bridge. NYSTA
After more than a decade of delays, the New York State Thruway Authority and the State of New York are preparing to kick off construction of the replacement for the Tappan Zee Bridge across the Hudson River in upstate New York.
March 26, 2013—Construction will begin this spring on the largest transportation design/build project to date in the United States, New York State’s replacement for the Tappan Zee Bridge. The 16,000 ft long bridge will span the Hudson River between Westchester and Rockland in upstate New York, about 25 mi north of New York City, replacing an existing bridge that is nearly 60 years old. Designated a high priority in 2010 by President Obama, the Tappan Zee Bridge replacement is the largest of three accelerated Transportation Infrastructure Finance and Innovation Act (TIFIA) highway bridge projects currently under way in the nation.
In January the New York State Thruway Authority (NYSTA) approved a $3.142-billion design/build contract with Tappan Zee Constructors (TZC). TZC, a consortium comprising Fluor Enterprises, American Bridge Company, Granite Construction Northeast, and Traylor Brothers, was selected above two other final bidders. A selection committee that included local community leaders and representatives from Westchester and Rockland counties, the State of New York, and NYSTA, as well as experienced design, construction, and planning professionals, considered the quality of each design’s technical, environmental, and bridge features—as well as price—in its decision.
TZC’s plan required the smallest number of columns and least disruptive foundations compared with the other two final contenders, with associated reductions in hydro-acoustic and suspended sediment impacts and construction noise. The winning design also featured the lowest cost and shortest construction timeline—five years, two-and-a-half months—according to Thomas J. Madison, the NYTSA’s executive director.
The selection committee also cited TZC’s “efficient structural arrangement in the approach and main span structures leading to superior visual transparency” and its narrower footprint at the landings, which will require fewer property acquisitions and have less of an impact on historic architectural resources, according to Mark Roche, C.Eng., A.M.ASCE, a senior engineer for Arup who has served for some time as a consultant to the NYSTA on the project.
The design consists of two parallel four-lane, cable-stayed bridges
with two emergency lanes, extra-wide shoulders, highway-speed
toll lanes, and a pedestrian/bicycle lane on the northern span.
TZC’s design consists of two parallel four-lane, cable-stayed bridges with two emergency lanes, extra-wide shoulders to accommodate enhanced express bus service and emergency vehicles, three highway-speed EZ Pass lanes at the toll booth, and a pedestrian/bicycle lane on the northern span. “The key to cost-efficient construction is the bridge’s long and repetitious form and structure,” says Roche.
After also considering dual-level and arch designs, the selection committee determined that the single-level, dual-span, cable-stay design aligned most closely with the NYSTA’s economic, environmental, and aesthetic criteria. The bridge substructure will use 350,000 tons of concrete; the superstructure will use 200,000 tons of concrete. The bridge’s steel superstructure will be constructed of 110,000 tons of American-made steel.
The existing Tappan Zee Bridge is a main commuter access route from the Westchester-Rockland corridor to New York City. The original bridge, built to last for 50 years, opened in 1955 and now handles more than 138,000 vehicles a day, 40 percent more than it was designed to accommodate, according to the NYSTA. With no nearby alternative routes, commuters frequently deal with traffic jams and long delays.
The old bridge has significant safety concerns, according to Madison. “The bridge does not conform to current safety standards, and it lacks lanes or shoulders for emergency access or disabled vehicles,” he says. “The volume of traffic and narrow lanes contribute to an accident rate on the bridge that is double that of the rest of the New York Thruway.”
Although express bus service does operate on the bridge, the structure cannot be expanded to accommodate such future mass transit needs as commuter rail. The NYSTA estimated that keeping the existing bridge would require an investment of $3 to $4 billion for a major structural overhaul and upgrades to its seismic protection.
After also considering dual-level and arch designs, the selection
committee determined that the single-level, dual-span, cable-stay
design aligned most closely with the NYSTA’s economic,
environmental, and aesthetic criteria.
The Tappan Zee Bridge replacement will be constructed just north of the existing bridge and will use the existing landings in Westchester and Rockland to minimize construction traffic in local communities. “Protecting local river towns from construction impact is an ongoing concern,” Madison says.
The NYSTA has been careful to cultivate a positive relationship with local communities impacted by the bridge, conducting more than 115 public meetings on the project. “Location of the landings, the piles, and the staging areas has been a major consideration,” Roche notes. Air and noise monitors will be installed to ensure the disturbance to local communities is minimized, he adds. To promote the bridge’s connection with the local communities, the new bridge will offer safe scenic overlooks with anti-climb fencing and security cameras monitored 24 hours a day.
TZC’s approach to the bridge’s design and construction combines environmental protection with innovation to maximize efficiency. The TZC and the NYTSA have been looking closely at how to mitigate the effects of construction noise that will come from the installation of the bridge’s nearly 1,000 4 to 6 ft diameter steel piles. “The state already has made significant investment in soil sampling and test pile-driving to provide as much information as possible to understand the noise impact on surrounding communities and the project’s environmental impact,” Madison says.
“In our pile demonstration program, we tested pile-driving and vibration techniques,” Roche says. “We have ascertained that we can vibrate the piles either all the way down, or within 50 feet of their final position.” The vibration technique will minimize noise for the nearby communities and for the fish in the river—a second consideration. Piles will need to be sunk to depths of between 300 and 350 ft, and geotechnical testing has determined that the foundations will rest on a mixed surface of rock and soft material. This month TZC will begin test borings in the river and in April crews will conduct on-site pile testing.
The TZC team is also taking precautions to minimize the disturbance to the endangered fish species in the Hudson River by applying state-of-the-art environmental mitigation measures, Roche says. A bubble curtain will surround the pile-driving areas as well as other heavy equipment as construction progresses to protect the fish from vibrations and sound waves passing through the water.
The Tappan Zee Bridge replacement will be constructed just north
of the existing bridge and will use the existing landings in
Westchester and Rockland to minimize construction traffic in
local communities. NYSTA
TZC will make the most of the river’s capabilities during construction. Later this year, the Left Coast Lifter, purported to be the world’s largest floating crane, will be towed to the site from New York City and positioned by GPS. The crane first saw service in Oakland, California, in 2009, when it was used to erect the new eastern span of the San Francisco-Oakland Bay Bridge.
Mounted on a barge, the 328 ft shear leg boom has an operating angle range between 19 degrees and 65 degrees with a capacity of 3.75 million lb (the equivalent of 12 times the weight of the Statue of Liberty) at the 65 degree point. “The crane’s extraordinary lifting weight and angle capacities will allow the largest section of the bridge to be positioned easily and at lower cost,” Madison notes.
The use of the crane will also mean that less dredging will be required to allow for construction access in the river’s extensive shallows, he adds. “The crane is mounted on a barge with a relatively shallow draft, which minimizes the amount of dredging required,” he explains. The plan will require about 950,000 cu yd of dredging compared with 1.5 million and 1.8 million cu yd required by the other proposals that were under consideration.
The Tappan Zee Bridge replacement will be constructed just north of the existing bridge and will use the existing landings in Westchester and Rockland to minimize construction traffic in local communities. aesth“Being able to utilize the river for material transport and storage will help minimize traffic and other impacts to the river towns and counties,” Roche says. “We are fortunate that we are building in a river where there is a lot of space available.” The New York Thruway, which connects directly to the project, will be used to bring in any materials that cannot be transported by barge, he adds.
Among the requirements spelled out in the request for proposals was that the new bridge not require major repairs or alterations for the next century. This made preparing the new bridge to accommodate commuter rail in the future a top consideration in TZC’s design, Roche says.
“With a vision that we are building a bridge to last more than 100 years, another goal of the NYSTA was to incorporate a lot of flexibility to ensure adaptability for potential changing demands in the years ahead, depending on the transportation plans in the surrounding counties,” he explains. “These future-proofing and long-life performance requirements were a challenge for the TZC designers, whose form-follows-function approach had to account for highway now, and potentially commuter rail in the future.”
TZC’s solution is a design that incorporates a series of tilted towers along the sides of the main span and foundations for future rail service that would run between the bridge’s two sets of lanes. When it’s time to construct the rail system, horizontal beams will be added between the main-span towers, connecting them at the roadway level and at the top. “This will create a central triangular tower form that has the necessary structural strength and stiffness to accommodate commuter rail,” Roche explains. “Modifications can be made directly to the bridge with no additional impact on the river.”
The total Tappan Zee Bridge project is expected to cost $3.9 billion, a figure that includes all preliminary testing and studies as well as the design/build expenditures. The project will be funded by toll revenues generated by the new bridge, supporting toll revenue bonds, and a $1.5-billion TIFIA loan announced by New York Governor Andrew Cuomo’s office earlier this month. New York State continues to seek additional financial support from federal, state, and local sources to reduce costs and keep tolls on the bridge low.