Every day about 140,000 cars and trucks cross the massive, seven-lane Tappan Zee Bridge connecting the northern suburban counties of New York City. Most drivers have no idea the 57-year-old bridge was designed in such a way that if just one of its structural elements gives way, the whole bridge could fall and send them tumbling into the Hudson River. The same is true for the Pulaski Skyway between Newark and Jersey City, and the San Diego-Coronado Bridge in California, not to mention the Fremont Bridge in Portland, Ore., the Lafayette Bridge in St. Paul, Minn., and thousands of others across the country.
Five years after the Minneapolis I-35W span suddenly collapsed in August 2007, killing 13 people and injuring 145 others, the U.S. still has 18,000 similarly designed spans, known as fracture-critical bridges, that need continual attention and money for inspections at a time when funding for maintenance is drying up. On March 31, the current extension to the federal highway bill, which funds work on bridges, will expire. Congress has been working on new legislation since the fall, getting nowhere. The Senate passed a two-year, $109 billion highway spending package on March 14 that would raise money for transportation projects by changing how pension fund contributions and liabilities are calculated. House Speaker John Boehner (R-Ohio) is pushing a five-year bill that calls for using royalties from U.S. oil and gas drilling—a proposal he hasn’t been able to sell to his own party.
The delays and political bickering aren’t reassuring for commuters who rely on the San Diego-Coronado or any of the other fracture-critical bridges. “They don’t give any warning at the point of collapse,” says Thomas Fisher, dean of the College of Design at the University of Minnesota. “It is sudden and catastrophic.”
Engineers still build fracture-critical bridges, but they do so with stronger steel and more sophisticated welding and riveting than they used in the 1960s and 1970s. The clock is ticking on the bridges built back then—like the former Minneapolis I-35W span, completed in 1967 and 40 years old when it gave way. Andrew Herrmann, president of the American Society of Civil Engineers, a Reston (Va.)-based industry association, says the average fracture-critical bridge from that era has a life of about 50 years. “These bridges have an amazing safety record to this point,” Herrmann says, “but they are getting old and have to be watched.”
U.S. Department of Transportation rules say states must inspect every bridge that’s 20 feet or longer at least once every two years. The agency lets state officials decide whether to put fracture-critical structures on a stricter schedule; some need more frequent inspections, depending on the steel grade and the weather and traffic they’re exposed to.
It’s labor-intensive work. Engineers use boats, cranes, and cherry pickers to get within arm’s reach of a bridge, looking for signs of corrosion or wear. Even miniscule cracks—as small as an eighth of an inch—can spell danger. “If the crack is not arrested, it can run the length of the steel and jeopardize the integrity of the structure,” says Michael Johnson, chief of specialty investigations for the California Department of Transportation. The state requires divers to do underwater inspections of its 214 fracture-critical bridges every five years.
“When you notice something on these bridges, they have to be shut down right away,” says the University of Minnesota’s Fisher. “It’s not like they sag or start to shake first.” That was the case last year when engineers discovered fissures as wide as a soda can on the Sherman Minton Bridge that straddles the Ohio River, connecting Kentucky and Indiana. The 50-year-old span closed in September 2011 and reopened last month after workers finished attaching 2.4 million pounds of steel plating for reinforcement along the sides of the bridge. It carries 80,000 cars and trucks a day.
The hands-on inspections can cost five to 15 times more than a standard visual checkup using binoculars, reaching into the six-digits and eating up state budgets. State and local governments pay up front for the inspections, then apply for reimbursement from Washington to cover a portion of the work. Keeping up that maintenance could become a problem in October. That’s when the federal pot of money that helps pay for bridge inspections and repairs, known as the Highway Trust Fund, could run dry, according to the Congressional Budget Office. The fund derives its revenue from fuel taxes, which have declined over the last three years as Americans began driving more fuel-efficient cars and buying less gas because of higher prices.
The dwindling money means state officials need to be more vigilant than ever, says Robert Connor, associate professor of civil engineering at Purdue University in West Lafayette, Ind., who studies fracture-critical bridges. “I don’t think the sky is falling today,” says Connor. “But if we don’t train the future workforce in at least how to maintain these structures, we’re going to have some pretty bad things eventually happen.”