Matt Coyne| The (Westchester County, N.Y.) Journal News
WHITE PLAINS, N.Y. — Since the start of the year, workers have laid down a number of road deck panels on the new Tappan Zee Bridge and its eight main span towers have begun to rise.
With that progress comes more things for residents to wonder about as the nearly $4 billion crossing comes together. Here are a few we've heard recently, and some answers:
Question: Why is the new bridge so much taller than the existing one?
Answer: It is and it isn't. The new bridge will have a different grade than the current bridge to help traffic flow better and to accommodate commuter or light rail.
At their highest points, both the current and new bridge will be 139 feet above the Hudson River.
The current bridge's grade rises from 0% to 3% between the Rockland landing and the main span, where the bridge's steel superstructure sits. On the new bridge, the grade will be 1.5%. With a gentler incline, trucks and cars will not slow as they reach the main span, helping to improve the traffic flow and reducing noise.
The other factor in the shallower grade — a potential rail line linking Rockland and Westchester counties — is still a long ways out. The bridge's 28-member mass transit task force recommended that trains be a long-term goal, meaning don't count on rail for at least 15 years from the bridge's expected completion in 2018.
Q: The new TZB will be the state’s first cable-stayed bridge. What does that mean?
A: The current Tappan Zee Bridge is a truss bridge, or a bridge where a steel superstructure helps support the road deck. Its replacement is taking a different approach.
The new Hudson River crossing uses cables in its design, like a suspension bridge such as the George Washington Bridge. On a suspension bridge, cables run from tower to tower with secondary cables supporting the crossing.
With a cable-stayed bridge, like the new TZB, the cables attached to the towers directly support the road deck. The towers are the primary load-bearing structure, with only vertical weight reaching the bridge's foundation.
In a truss bridge, like the current TZB, the superstructure helps the bridge deal with the forces being exerted on it.
Q: Are they really spending $100,000 on a new falcon nest?
A: The Tappan Zee Bridge has become home to a pair of peregrine falcons, who return to a nesting box atop the bridge each year in February and — if all goes well — stay to raise a family through the end of the summer.
When the new bridge opens, the falcons will go, too.
Transferring the birds to the new bridge carries a reported $100,000 price tag, which might leave residents to wonder if a fireplace, wine and some smooth R&B music is set to be included in the once-endangered birds' new home.
That $100,000 represents an estimate on the part of the Thurway Authority for budgeting purposes and may not reflect the actual cost of demolishing the old box and rebuilding it on the new bridge in a location approved by the state Department of Environmental Conservation, a project spokesman said. The bridge's falcon cam — a web camera trained on the nest box that allows people to watch the birds' activities — will be part of the move.
Q: When will the towers take shape?
A: The eight 419-foot towers will be the new bridge’s most striking feature — and they’re actually already going up.
Work on the towers started in September when the Thruway Authority announced the bridge was halfway complete. Earlier this month, crews installed the first crossbeam, weighing 650 tons, between two of the towers-to-be with the help of the project's massive crane. The crossbeams, four in total, were fabricated in Virginia and ferried up the east coast to the construction site.
Work will continue on the towers, made of steel-reinforced concrete sourced in the U.S., through the spring. They are expected to be completed by the end of the year.
As the towers continue to rise, they will narrow, and cables supporting the road deck will be connected. Crews will then be able to install the steel girders on top of which the road deck will sit.
Q: What other projects are happening in connection with the bridge?
A: Crews have put in work on either shore, including building an all-electronic toll system for the current bridge, set to go live this spring, putting in noise barriers and retaining walls for a shared-use path in South Nyack and building a new Thruway Authority maintenance office in Tarrytown.
When the electronic tolling system is complete, drivers will be able to roll through without stopping, with EZ-Pass holders charged electronically. Those without EZ-Passes will have bills mailed to them.
Follow Matt Coyne on Twitter: @coynereports
