Colossal Construction

Just north of New York City, a massive construction project is under way—the first major bridge built in New York State in 50 years. Last June, I visited the site to check on its progress. From a tiny boat on the Hudson River, I watched as workers climbed up the bridge’s massive towers—each taller than the Statue of Liberty—and bolted huge steel girders into place.

For the past four years, builders have worked around the clock to complete the bridge. This fall, the first half of the bridge opened to the public. When it’s finished, two side-by-side roadways will stretch 5 kilometers (3.1 miles) over the river. Together, they will carry nearly 140,000 vehicles per day, helping everyone from commuters to truck drivers get to their destinations in one of the busiest regions in the country.

A massive construction project is under way just north of New York City. It’s the first major bridge built in New York State in 50 years. Last June, I visited the site to see how it was going. I watched from a tiny boat on the Hudson River. Workers climbed up the bridge’s massive towers, each taller than the Statue of Liberty. Then they bolted huge steel girders into place.

Builders have worked on the bridge around the clock for the past four years. This fall, the first half of the bridge opened to the public. When it’s finished, the bridge will have two roadways, side by side. They’ll stretch 5 kilometers (3.1 miles) over the river. Together, they’ll carry nearly 140,000 vehicles per day. Everyone from commuters to truck drivers will use the bridge. It will help people reach their destinations in one of the busiest areas in the country.

The Governor Mario A. Cuomo Bridge will replace the nearby Tappan Zee Bridge, which was built in 1955. The Tappan Zee is two years beyond its planned life span.

Although the Tappan Zee isn’t about to fall down, it is overburdened, carrying more vehicles than its designers intended. The roadway is steep, it doesn’t have shoulders, and emergency access is poor. Because of these conditions, the accident rate on the bridge is double that of most highways in New York, says Jamey Barbas, who runs the project for the New York State Thruway Authority. She is a civil engineer—a type of engineer who designs, builds, and supervises construction projects.

The Governor Mario A. Cuomo Bridge will replace the Tappan Zee Bridge. This nearby bridge was built in 1955. It’s two years past its planned life span.

The Tappan Zee isn’t about to fall down. But it’s carrying more vehicles than it was built to handle. The roadway is steep, it doesn’t have shoulders, and emergency access is poor. These conditions lead to accidents. Twice as many accidents happen on the bridge than on most highways in New York, says Jamey Barbas. She runs the project for the New York State Thruway Authority. She’s a civil engineer. This type of engineer designs, builds, and supervises construction projects.

The Thruway Authority has spent hundreds of millions of dollars repairing the Tappan Zee. But pouring more money into old bridges doesn’t always make sense. Even though the new bridge will cost nearly $4 billion in the end, the high price tag will be worth it, says Barbas. “It should last 100 years without any major reconstruction,” she says.

The Thruway Authority has done a lot of work on the Tappan Zee. The repairs have cost hundreds of millions of dollars. But spending more money on old bridges doesn’t always make sense. The new bridge will cost nearly $4 billion, but Barbas says the high price will be worth it. “It should last 100 years without any major reconstruction,” she says.

New York Governor Andrew M. Cuomo kicked off construction on the new bridge in 2013. Engineers chose a cable-stayed bridge for its design (see A Better Bridge). This type of bridge relies on cables strung from towers to the road deck below. The tension, or pulling force, along the cables helps support the weight of the bridge. “It’s the most cost-effective design for a bridge of this length,” says Barbas.

New York Governor Andrew M. Cuomo started construction on the new bridge in 2013. Engineers chose a cable-stayed bridge for its design (see A Better Bridge). This type of bridge has cables strung from towers to the road deck below. This creates tension, or pulling force, along the cables. The force helps support the bridge’s weight. “It’s the most cost-effective design for a bridge of this length,” says Barbas.

The bridge is being built from the riverbed up. More than 1,000 steel piles were driven deep under the riverbed to form a base. Ideally, these cement-filled pipes should sit on bedrock. But in some areas, that solid layer of underground rock was too deep to reach. In such areas, the piles are supported by friction. The clay, silt, and other sediment under the riverbed rub against the surface of each pile. The resulting resistant force is strong enough to steady the piles so they can support much of the bridge’s weight.

Once the piles were in place, barges carried pre-made 122 meter (400 foot)-long steel sections of the two roadways from a construction site upriver. A floating “supercrane” lifts the sections into place. When construction finishes in 2018, the piles and cables will support two roadways with four general-use lanes each, emergency access, and room for future mass transit.

The bridge is being built from the riverbed up. More than 1,000 steel piles were driven deep under the riverbed. These cement-filled pipes form a base. The best spot to place them is on bedrock. But in some areas, that solid layer of underground rock was too deep to reach. In those areas, friction supports the piles. Clay, silt, and other material under the riverbed rub against each pile. The result is a force that’s strong enough to steady the piles. It allows them to support much of the bridge’s weight.

After the piles were in place, barges carried in steel sections of the two roadways. The sections are 122 meters (400 feet) long. They were pre-made at a construction site upriver. A floating “supercrane” lifts the sections into place. When construction finishes in 2018, the piles and cables will support two roadways. Each will have four regular lanes, emergency access, and room for future mass transit.

One of the biggest challenges of the project is its location. The bridge spans a tidal estuary, where freshwater flowing down the Hudson River from upstate New York mixes with saltwater from the Atlantic Ocean. Project planners had to pledge to protect this delicate ecosystem and the many vulnerable species within it, says Kristine Edwards. As the project’s environmental compliance manager, it’s her job to monitor work at the construction site to make sure it adheres to environmental regulations.

To begin construction, workers needed to dredge, or dig out, the riverbed to make it deep enough for barges to carry materials and equipment. They used special machinery that reduced the river’s turbidity—cloudiness caused by particles in a fluid—as sediment was stirred up by digging. High turbidity can fatally clog fish’s gills. Project planners also agreed to dredge only from August 1 to November 1 to avoid harming endangered sturgeon, a type of fish that swims upstream and back to spawn.

One of the project’s biggest challenges is its location. The bridge spans a tidal estuary. Freshwater flows down the Hudson River from upstate New York. At this spot, it mixes with saltwater from the Atlantic Ocean. This creates a delicate ecosystem with many species that could easily be harmed. Project planners had to promise to protect them, says Kristine Edwards. She’s the project’s environmental compliance manager. Her job is to make sure that work at the construction site follows environmental regulations.

Workers needed to dredge, or dig out, the riverbed to begin construction. This made it deep enough for barges to carry materials and equipment. The digging stirred up sediment. So workers used special machinery to lessen the river’s turbidity. That’s the cloudiness caused by particles in a fluid. High turbidity can clog fish’s gills and kill them. Project planners also agreed to dredge only from August 1 to November 1. That way, they wouldn’t harm endangered sturgeon. This type of fish swims upstream and back to spawn.

Workers needed to minimize the noise that came with hammering the bridge’s piles into the ground too. The vibrations from construction equipment can rupture a fish’s swim bladder—a gas-filled organ that helps fish move up and down in water. To protect the sturgeon and other fish from noise, engineers installed a “bubble curtain” around piles. This wall of air reduced the amount of noise escaping into the river.

The bridge’s piles were hammered into the ground. Workers needed to lessen the noise that this caused. Vibrations from construction equipment can burst a fish’s swim bladder. This gas-filled organ helps fish move up and down in water. Engineers found a way to protect the sturgeon and other fish. They placed a “bubble curtain” around piles. This wall of air lowered the amount of noise escaping into the river.

Massive infrastructure projects are costly and difficult. Once the new bridge is finished, workers will have to begin carefully dismantling the old one. The Tappan Zee Bridge will be taken apart piece by piece and shipped away on barges. Although the process is hard, it is also necessary. “What we’re working toward is a better future,” says Barbas. “That’s the beauty of civil engineering.”

Massive infrastructure projects are costly and difficult. When the new bridge is finished, workers will have another task. They’ll begin to carefully take apart the Tappan Zee Bridge. They’ll ship the pieces away on barges. The process is hard, but it’s also necessary. “What we’re working toward is a better future,” says Barbas. “That’s the beauty of civil engineering.”