http://www.thejournalnews.com/apps/pbcs.dll/article?AID=/20060917/NEWS02/609 170348/1020/NEWS04
Tappan Zee Bridge is a lifeline vulnerable to attack By JORGE FITZ-GIBBON AND BRUCE GOLDING THE JOURNAL NEWS (Original Publication: September 17, 2006) When the gale-force winds buffeting its aging beams started to topple tractor-trailers on the Tappan Zee Bridge, state officials took the unprecedented step of stopping all traffic on the three-mile span. The move paralyzed the Lower Hudson Valley for more than three hours as thousands of motorists were stranded, and raised the specter of what would happen if the bridge was somehow knocked out of commission. With an earthquake fault beneath it and rust attacking its steelwork, the Tappan Zee is in fact vulnerable to a number of scenarios that could shut down the Hudson River crossing - perhaps permanently. Whether it's a terror attack, a natural disaster, or the accidental crashing of a barge or freighter, there's only so much that can be done to protect the bridge, says the New York State Thruway Authority, which owns and operates the span. "You have to live with a certain amount of risk," said Ramesh Mehta, the Thruway's Hudson Valley Division director. "And I don't think we can cover all the risks. ... But then we can take some precautionary measures, which we are taking at this time as an organization." Some possibilities are more likely than others, and some have been confronted by the Thruway Authority. But officials and outside experts agree: The threats are real. Across the country, at least two major bridges have been brought down by stray barges in the past five years, killing nearly two dozen people. In Cameron County, Texas, four loaded barges pushed by a tugboat struck the Queen Isabella Causeway, the state's longest bridge, on Sept. 15, 2001. The barges hit one of the columns and knocked down two 80-foot sections of the span. A third 80-foot section fell later. Eight people were killed in the accident, and 13 were rescued from the water. In May 2002, the 1,988-foot-long Interstate 40 bridge over the Arkansas River in Webbers Falls, Okla., was struck by one of two barges traveling north on the river. The barge hit a pylon about 7:30 a.m. in a heavy storm. About a dozen vehicles plunged 60 feet into the water below when a 600-foot section of the bridge collapsed. Fourteen people died. A study sanctioned by the Thruway Authority 12 years ago found that the Tappan Zee's two main piers - the water-level sections of the towers that support the span over the main shipping channel - would collapse if struck by a large-enough vessel. In addition, the Tappan Zee's original steel and timber fender system had decayed because of weathering. "It said the existing system was not very good, and they thought that since the size of the ships are increasing, they're carrying more load, and if by any chance they hit the pier, there was a danger of collapse," Mehta said. A federally mandated inspection later found more problems with the aging piers. The authority initially shored them up with emergency repairs, and later paid for a full upgrade. In all, the work cost more than $60 million by the time it was finished in 1999. Neal Bettigole, a retired bridge designer who has worked on the Tappan Zee, said a barge strike now probably would not collapse the bridge. But, he added, "you can never say never." Anti-terrorism measures have been stepped up on the Tappan Zee, but experts say it will always be vulnerable to attack. Even before the Sept. 11, 2001, terror attacks, keeping major transportation routes intact has been a vital concern of federal officials. The Tappan Zee Bridge is no exception. "There's no question that if the bridge were to be brought down by a bomb, that would have an enormous domino effect on the entire metropolitan area," said Ralph M. Stein, a professor at the Pace University School of Law in White Plains. "I personally believe it's a more serious target than Indian Point. Indian Point is solid. You need to crash a very big plane into it, and they claim that even a Boeing 707 wouldn't do it. And it's got high security. If you had even a medium-size plane and you hit those spans and brought down a span, the bridge is out." Although the Tappan Zee has not been mentioned specifically, several of the region's river crossings have been targets in past terror plots. In 1993, federal authorities foiled a plot by blind Muslim cleric Omar Abdel-Rahman that included blowing up the George Washington Bridge and other major targets in New York City. In 2002, security was doubled on the Golden Gate Bridge after the bridge appeared in a videotape seized in Spain. Officials said al-Qaida may have also considered targeting the Brooklyn Bridge. This summer, authorities foiled a terror plot that was meant to blow up bridges and tunnels in Manhattan. The alleged conspirators were arrested while the plan was still in its infancy. At 50 years old, time could be the biggest threat to the Tappan Zee. A 2004 inspection revealed that the span's safety railings could fail and that some steel beams had been eaten clear through by years of corrosion. Some support bearings were off-center and missing significant amounts of concrete. Those findings came despite more than $316 million in repairs and upgrades between 1995 and 2004, fixes that still left the bridge with some of its lowest federal safety ratings in more than a decade. One of the bridge's most pressing problems is the roadway, which averages about one "punchthrough" hole - an opening in the pavement clear through to the river below - each month. The Thruway Authority this year awarded a $147 million contract, the largest ever to fix the bridge, to replace nearly half of the deck and repair crumbling concrete. In May, crews inspecting the bridge shut down two Westchester-bound lanes at the height of the morning rush to conduct emergency repairs. The decision was made after the discovery of deteriorated "finger joints," the metal parts that hold slabs of roadway pavement in place. The Thruway Authority said there was no similarity to problems that caused the region's worst bridge collapse: the failure of the Mianus River Bridge on Interstate 95 in Connecticut. On June 28, 1983, a 100-foot section of the eastbound span fell 70 feet into the river below, killing three. It was later determined that the road gave way after rusted pins that held one corner of the section failed because of corrosion, leaving the entire weight of the deck supported by pins on just three corners. They ultimately gave out. The support system on the Tappan Zee is radically different, Mehta said. However, he said, the Mianus bridge collapse prompted special attention to support pins and bearings, including on the Tappan Zee. Although trucks carrying explosives are banned from the Tappan Zee, an accident involving combustible cargo is always a possibility. Mehta said inspectors have never studied the potential damage from such a blast but would do so. "It all depends on how it explodes and what direction it goes," he said. "We don't know that yet. It would be very difficult to assess that, because there are a lot of openings also, because it's a truss span. If the debris can go through the truss or through those openings ... it can be very vulnerable." In March 2004, an oil tanker crashed on I-95 in Bridgeport, Conn., and burst into flames on a Friday morning, forcing officials to shut down the roadway in both directions. The tanker was carrying 9,000 gallons of heating oil when it hit a car, jackknifed and caught fire. Heat from the blaze buckled part of the Howard Avenue overpass above the highway. In October 1997, a tractor-trailer carrying 8,800 gallons of gasoline was hit from behind by a car and burst into flames beneath an Interstate 87 overpass in Yonkers. The truck driver tried, but failed, to rescue the other motorist from his burning car. Damage to the steel and concrete of the overpass forced its closing and eventual replacement. And in July 1994, a truck driver was killed and more than 20 people injured when a propane truck exploded on Interstate 287 in White Plains. At least four nearby homes caught fire after the truck crashed into an overpass at Grant Street, rocketing the propane tank through the air spewing flaming fuel. The accident shut down the highway, but repair crews fixed the damage enough to reopen all lanes within 24 hours. Federal research has determined that bridges are the part of the nation's highway system most vulnerable to earthquakes, as was dramatically shown during the 1989 Loma Prieta earthquake in California. More than 80 bridges were damaged and more than 40 motorists died in bridge-related collapses alone, according to the government's Turner-Fairbank Highway Research Center. Like most bridges built in the United States before 1970, the Tappan Zee was not designed with earthquakes in mind, even though it is located in a seismically active area atop a belt of ancient rock known as the Manhattan Prong. During the early 1950s, Columbia University geologists found a fault line running through the bedrock under where the Tappan Zee sits, about 1,250 feet off the Tarrytown riverbank. The fault hasn't shown any activity since its discovery, and the bridge wasn't damaged by a 4.1 magnitude earthquake centered in Ardsley that shook five states and Canada in 1985. But studies dating to at least 1995 warn of danger from ground movement, and an extensive April 2000 report on the bridge's future said keeping the Tappan Zee in service would require retrofitting it to withstand seismic activity, "particularly its most vulnerable causeway segment and several foundations under the main span and other spans." The likelihood of a magnitude 6.0 earthquake that would cause enough damage to close the bridge for several weeks is about 1 in 1,000 in any given year, and the risk of a magnitude 7.0 earthquake that could bring the bridge down is about 1 in 10,000, said Klaus Jacob, a geologist who worked on a 1995 seismic study of the Tappan Zee fault. Motorists shouldn't worry too much about earthquakes while crossing the span, he said. "They have occurred in the East Coast, but they're so rare that there's a good chance other things will happen first," said Jacob, former senior research scientist at Columbia University's Lamont-Doherty Earth Observatory. The Tappan Zee Bridge also faces the possibility of damage from the winds that blow through the Lower Hudson Valley. The 2000 report on the bridge's future noted that "research has shown that the wind loads on bridges are actually greater than those that the Tappan Zee Bridge was designed to withstand. These increased load requirements have taxed the reserve strength built into the bridge." In July, the Tappan Zee dodged a bullet when the tornado that tore across southern New York blew by just north of the bridge. Motorists saw the waterspout as it crossed the river, but work crews later found no signs of impact, although a shed on a nearby barge was slightly damaged. The bridge doesn't have to be affected for high winds to pose a threat to motorists, as happened in January, when fierce winds toppled two empty tractor-trailer trucks, one of which was later righted by the wind, then pushed over a second time. Officials stopped traffic on the bridge for almost three hours as the winds - which gusted to 70 mph - continued to blow. The Thruway Authority has protocols for warning motorists and reducing the 55 mph speed limit to 45 mph when there are sustained winds of more than 30 mph. The speed limit is reduced to 35 mph when the wind blows at 40 mph or gusts to 45 mph, and trucks, buses and motorcycles are banned at wind speeds of 50 mph or gusts of 55 mph. All traffic is supposed to be diverted when the wind reaches 65 mph, but the January incident marked the first time the Tappan Zee was closed because of high winds, said Mehta, the Thruway Authority's division director. "It almost closed by itself because of the overturned tractor-trailers," Mehta said. "Because everything was at a standstill, we thought it was best to close the bridge because of the high wind speeds." Although the bridge itself is constructed of concrete and steel, a large portion rests on wooden pilings driven into the riverbed. And as the Hudson River has become cleaner, the risk has risen that those pilings could fall prey to marine organisms called "shipworms." While they look like worms and can grow 2 feet long - even longer in warmer water - the creatures are a type of clam. They use their shells to bore into wood on boats, docks and piers. "These critters are responsible for keeping the rivers and lakes and oceans of the world relatively free of timber debris," said Bettigole, the retired bridge designer. "As far as I understand it, it's unlikely they're going to pass up two miles of untreated, yummy, wood piles." A state report last summer noted that shipworms and another marine borer - a small crustacean known as the "gribble" - had invaded waters throughout the Northeast and caused extensive structural damage in New York Harbor. Published reports during the 1990s also documented more than $100 million in spending by New York City to combat the pests. Mehta said that about 20 years of tests using wood panels suspended in water near the bridge had failed to turn up any trace of borers until this year, when evidence of shipworms was found in panels pulled from the river in March. No evidence of gribbles was found, he said. At this point, the Thruway considers the test results isolated and is continuing to monitor for signs of infestation, he said. Built in 1955, the Tappan Zee Bridge connects the New York State Thruway, linking Tarrytown and South Nyack at one of the Hudson River's widest points. It has become a major crossing for cargo trucks, as well as tens of thousands of commuters and tourists every day. "I don't know if you have any particular interest in World War II, but there's a reason why the Germans had flak guns on every bridge, because the bridges are vulnerable," said Stein, the Pace Law professor. "They're a throat of commerce. I mean, what are you going to do, put anti-aircraft guns on the bridge? Have swimmers around the bridge? I don't know what you're going to do." Mehta said bridge inspectors were tuned in to potential threats to the Tappan Zee, and routinely assessed and addressed them. But he echoed the harsh reality that there was a limit to what they could do. "They know that there are some known vulnerabilities, like the earthquake, like the wind speed, and all those things," Mehta said. "So I think those things are being looked at at this time. ... "I think there's limitless vulnerability on the bridge, and the more we do (inspections), the more we can identify." 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