After pouring hundreds of millions of dollars into maintenance and repairs to the deteriorating Tappan Zee Bridge over the past decade, Gov. Andrew Cuomo says he wants a bridge that will stand on its own for a century.
Bridge designer extraordinaire Ted Zoli said there”™s no reason to think the governor can”™t get his wish ”“ and then some.
Designing a bridge whose various elements can be replaced without significantly affecting traffic or the environment is “the challenge of our time, as engineers,” said Zoli, vice president and national bridge chief engineer for HNTB, a civil engineering, architecture, planning and construction management firm based in Kansas City.
“If the elements ”“ especially the elements that will wear out ”“ are replaceable, that represents a good bridge because it”™s a bridge where you maintain your large capital investment, and then your ability to fix it and maintain it will extend its life,” said Zoli, whose portfolio includes the Leonard P. Zakim Bunker Hill Bridge in Boston, the Bob Kerrey Pedestrian Bridge in Omaha, Neb., and most recently, the Lake Champlain Bridge between New York and Vermont.
Accounting for wear and tear and enabling the future addition of some form of mass transit are among the biggest issues facing the four design-build teams competing for the contract to build the new Tappan Zee, and will likely be the biggest source of variation between the four teams, Zoli said.
HNTB is a member of the Hudson River Bridge Constructors team, one of the four finalists, whose principal contractors include Dragados USA Inc., Flatiron Constructors Inc., Samsung C&T, E&C Americas Inc. and Yonkers Contracting Co. Inc.
While bridge-building has come a long way since the original Tappan Zee opened, Zoli said much of the new bridge”™s design will be dictated by the amount of work crews will be required to perform over water, poor soil conditions, the prospect of building next to a heavily trafficked bridge and other environmental uncertainties that the builder won”™t be able to assess until they arrive on the scene in the fall.
The new bridge must also account for future mass transit, which could not have been added onto the current bridge due to its truss-based design, Zoli said.
The state has studied both cable-stay systems, such as the Bunker Hill Bridge in Boston, and arch systems, such as the Lake Champlain Bridge, but Zoli suggested the former is more likely.
“With this sort of environment, where you have poor soils on either side, getting horizontal forces into the ground if it were a true arch or if it were a suspension bridge is not ideal,” he said.
Truss systems are lighter and simpler than cable-stay or arch systems, but the latter two are more cost-efficient from a labor standpoint, Zoli said.
Cable-stay systems “are not the most efficient systems but they”™re easiest to build, so we”™ve started to realize that the buildability of a system is much more influential in terms of decision-making for what”™s cost-efficient and what”™s not.”
The ultimate cost of the bridge will be based on how each contracting team accounts for the various environmental uncertainties and on how each team proposes to expand the bridge.
“I think what you”™ll find in the design-build submittals is there will be a range of what teams imagine as being generous enough about future expansion,” Zoli said. “Part of that is the cleverness of the design-build teams to come up with ideas that are synergistic, that maximize the opportunity for widening, for creating transit and yet integrating that well into the base design so that the cost difference is small.”
STANDARD & POOR”™S PREDICTS “AGGRESSIVE” TOLL HIKES
Amid speculation that the construction of a new Tappan Zee Bridge will require major toll hikes across the state, Thruway Authority officials last week said nothing would be determined until the finalists for the bridge contract submit their respective proposals.
Under the design-build process by which the new Tappan Zee will be built, the cost of construction will likely vary from bid to bid.
The final cost of the project and the state”™s financing options won”™t be determined until the Thruway Authority and the state Department of Transportation select a winning bid, which is expected to be by October.
Proposals are due to the state by July 27.
The credit rating agency Standard & Poor”™s said earlier this month that financing a new bridge would likely require the Thruway Authority to institute “aggressive” toll hikes.
S & P earlier in June affirmed its A-plus rating for the Thruway Authority”™s general revenue bonds, but lowered its outlook to negative, warning that travelers could be facing higher tolls as the state seeks to finance a new Tappan Zee Bridge.
“The negative outlook reflects our concern that the timing and magnitude of revenue enhancement and operational streamlining initiatives might not be enough to offset (the authority”™s) significant additional debt needs,” S & P said in its report.
The Thruway Authority is a tolling agency, meaning that it receives very little state or federal funding and instead relies on revenue from tolls to support its annual budget.
In all, the authority is responsible for managing more than 500 miles of highways stretching from Buffalo to New York City.
Thruway Authority Chairman Howard P. Milstein said in a statement that recent actions have set “a sound fiscal foundation” and “confirm that we are ready, willing and able to make the major investments needed in the future.”
Milstein added, “Our financial advisor is actively engaged in development of a comprehensive plan to finance the new Tappan Zee Bridge.”
S & P said that if the Thruway Authority institutes an “aggressive tolling regime” to offset the cost of the new bridge, expected to be $5.2 billion, the negative outlook could be upgraded to stable within two years.
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