The 3.1-mi. long Tappan Zee Bridge across the Hudson River approximately 20 mi. above New York City can be a beautiful or excruciating driving experience.
As they cross the span between Nyack and Tarrytown, NY, motorists often see white sailboats on a broad expanse of blue water stretching north and south between palisades and hills. However, when the traffic is backed up with thousands of vehicles, the beauty fades and grim frustration sets in.
Now the Tappan Zee’s days may be numbered. Planners are seriously considering replacing it with one the nation’s longest tunnels.
“A tunnel is definitely on the table as a solution,” said Chris Waite, executive project manager in Albany, NY, for the Tappan Zee/Interstate 287 environmental review.
“There is a possibility that a tunnel of some nature will be built, perhaps with multiple bores for the highway and another bore for commuter rail,” said Waite.
The bridge is approaching its design life of 50 years, and is badly corroded from salt and the wear and tear of cars. During holidays, it often carries 170,000 vehicles — well above the 100,000 of its original plans.
The New York Thruway Authority and New York City’s Metropolitan Transportation Authority, studying ways to alleviate the congestion, are considering a tunnel with from one to six bores which could each be 60 ft. in diameter.
A tunnel would be one tough job. First, it can’t disturb the environment. The river valley is really deep at this point in the Hudson’s graceful sweep to the sea. Glaciers carved out a sharp 800-ft. deep “V” right here, with gravel at the bottom and then clay and sand. The top 10 ft. or so is silt, which is most easily disturbed.
“As you go down further, the soil becomes more suitable for a bored tunnel. We just would have to determine how deep we need to go,” Waite said. “The river itself is usually only 10 or 15 ft. deep — 40 ft. deep at the channel. We would of course go under the channel.”
Then, too, there’s the challenge of appropriate equipment. Waite said some proposals call for 60-ft. diameter boring machines, larger than have been used before in the United States.
One observer told Construction Equipment Guide (CEG), a Tappan Zee tunnel might cost $650 million. Others said this figure is very low and that the tunnel would cost much more.
Proponents of the tunnel strongly argued their case when the project team held a public hearing last January on alternatives for the traffic corridor. One of these supporters, Alexander Saunders, the president of Foundry Supply Company Inc. in Cold Spring, NY, is a leading critic of the bridge.
“This damn bridge is very sick, Saunders told CEG. “It’s a great big bridge which is hopelessly jammed and which destroys views, louses up sailing and pours acid and gas every time they crash a car, which is three times a day, with a horrifying accident rate of 1,500 accidents a year. Much of the bridge is a low causeway. I want to see open water again. The public is demanding the Thruway Authority get the bridge out of there and look carefully at a tunnel instead of spending hundreds of millions to prolong the bridge’s life.”
Saunders goes even further. At environmental hearings, he has presented a plan for a 40-mi. tunnel under the Hudson at the Tappan Zee site, then under Westchester and Long Island Sound, emerging near Syosset, Long Island, where it would connect with expressways and relieve congestion around New York City (see sidebar). Waite, however, said this plan “is not on the table.”
The project team received more than 150 suggestions at the January hearing. Waite told CEG that these have been pared to roughly 15 scenarios.
“By January of 2004, we expect to screen these further to four or five,” he added. “We will analyze these as we prepare our environmental impact statement [EIS] until one pulls into the lead and becomes a clear preferred alterative. We expect to reach a record of decision [for one approach] with concurrence from the Federal Highway Administration and the Federal Transit Administration that the EIS has been properly carried out, by the end of 2005. At that point, we will probably engage a design firm.”
Waite said any tunnel would probably have to be a bored-type.
“Other types of tunnel, like submersible tubes, would cause too much disturbance to the riverbed, he said. We don’t yet know the exact composition of the silt. There could be contaminants, which would get back up into the water and migrate. We would want a bored tunnel to be as big as a tunnel boring machine could make it. We need to have full shoulders, ventilation equipment, maybe some stacked lanes [one on top of the other] if possible. I think there’s probably some economies in stacked lanes, with fewer big bores instead of more small bores. If we could stack the lanes two over two, it would save us a whole tunnel, a whole bore.”
Where would the tunnel begin and end?
“Primarily we’re looking at crossing the river,” Waite replied. “The grade hasn’t been decided yet. Depending on depth and rate of climb, you could add another three or four miles of tunnel length beyond the actual width of the river, so it could be six or seven miles long. I don’t think we want to stay underground any longer than we need to because we could wind up missing existing interchanges and changing everybody’s traffic patterns significantly.
A Tunnel for Transit?
The Tappan Zee is right in the middle of the 30-mi. circumferential Interstate 287 traffic corridor, often packed with traffic, between Suffern, NY, and Interstate 95 at the Connecticut-New York border. This corridor serves two distinct markets: east-west traffic back and forth between Rockland County, NY and Westchester County, NY, and north-south traffic to and from New York City.
A tunnel might well include an east-west transit service to cover these markets, or might even be extended to White Plains, NY.
“Five north-south commuter rail lines cross our corridor but there exists no east-west link between them other than the highway itself,” Waite said. “We’re looking at an east-west service which would be removed from, or at least less impacted by, the current congestion on the roadway. It’s unlikely that we could put commuter rail over the existing bridge. There are over 200 expansion joints in the Tappan Zee, so that makes it tough for heavy rail.”
Some of the remaining 15 scenarios include building a new bridge.
“We could replace the bridge and widen the road in Rockland County, Waite said. That’s a potential highway-only solution. We also have a potential transit-based solution where we would just add commuter rail to the corridor. How we cross the river remains to be seen. That could be a tunnel.”
Proposals to rehab or expand the present bridge also are still alive.
Discussing expansion, Waite observed: “The Tappan Zee now carries seven lanes, with the middle lane being reversible. Twice a day we move three miles of construction-type barrier back and forth to provide an eastbound or westbound lane. We would be better off with eight permanent lanes, but the bridge wasn’t built with a mind towards expansion.”
Is the present Tappan Zee safe?
“There’s no danger of a bridge failure as far as load or weight are concerned,” Waite said. “What happens is that someone is bound to get a flat tire or overheat and the whole thing gets snarled up because there are no shoulders, no breakdown lanes.”
What about the bridge’s impact on the environment?
“Exhaust fumes, of course, impact air quality,” Waite replied. “Air quality suffers when traffic is congested. Also, the bridge was designed with open drainage, so that everything runs off the side. That’s one of the reasons the bridge has deteriorated as much as it has. Road salt dripping has deteriorated the steel. The river is coping but we need a baseline —where the river is today, how we’re handling what we have, and what happens if we disturb the river by constructing a bridge or tunnel.”