Bridge-vessel collisions have taken a heavy toll recently. In September 2001, eight people died when Brownwater V and its barges hit the Queen Isabella Causeway in Texas (left). In May 2002, towboat Robert Y. Love and two barges struck an Interstate 40 bridge over the Arkansas River in Oklahoma (below), killing 14 people.
“This was not a bridge failure; this was a bridge knockdown,” said Bruce Taylor, chief engineer for the Oklahoma Department of Transportation, according to the Associated Press.
In fact, the National Transportation Safety Board and engineers have been warning for at least 10 years that many of the nation’s older bridges over waterways are extremely vulnerable to collapse when hit by ships.
When bridges are struck by ships, mariners are often blamed for the collapse, even though there is much that can be done to shield bridges from collisions and to make them less likely to collapse.
While hundreds of bridges may be vulnerable to blows from vessels, the precise number is unknown. During the 1990s, the NTSB repeatedly asked the Federal Highway Administration (FHWA) to come up with a national list of bridges vulnerable to collapse if struck by a ship. The FHWA has refused, stating in interagency letters that state transportation officials already had the resources to address this problem. Without a national policy, only a handful of states have gone ahead and done bridge surveys to assess the risk of ship collision. There are 482,000 bridges over waterways in the country, according to the FHWA.
The absence of hard data is troubling to some experts in the field.
“My main concern is that this group of older bridges is out there, and until we do that assessment, we don’t know if it’s a serious problem or a problem that we can deal with over time,” said Michael A. Knott, a vice president at Moffatt & Nichol Engineers’ Norfolk, Va., office.
Knott is an internationally known authority on the science of risk analysis for bridge collapse who has been working in the field for over 20 years. He believes not enough has been done on the national or state levels to solve this problem.
“My own theory is that not enough people have been killed yet,” he said. “As long as the loss of life is a small number, we just keep rolling by. It’s going to take some major, national tragedy before we get serious about it.”
There have been plenty of tragedies. Since 1964, 125 people have died in the United States in 17 major bridge collapses involving vessels. Two major collapses have occurred in the last year alone. On May 26, 14 motorists were killed when a towboat pushing two empty barges hit an out-of-channel pier on the I-40 bridge over the Arkansas River in Oklahoma. The towboat’s pilot may have had a heart attack just before the incident.
And on Sept. 15, 2001, eight people were killed when a towboat pushing four barges went about 300 feet off course and struck the Queen Isabella Causeway in Texas.
The country’s worst bridge collapse occurred on Sept. 22, 1993, when the towboat Mauvilla, operating in dense fog, pushed several barges into the Big Bayou Canot railroad bridge in Alabama. Eight minutes later an Amtrak train crossed the displaced bridge and derailed, killing 47 people.
In September 1994, the NTSB found that the pilot of the towboat lacked radar navigation competency. And it was in that report that the NTSB first recommended that a national survey be conducted to determine which bridges in the country were vulnerable to ship collision.
Acts of God
Before 1980, ship collisions with bridges were seen as an act of God, an event that could not be foreseen. After the May 1980 collapse of the Sunshine Skyway Bridge in Tampa Bay, Fla., engineers and public officials began looking at ways to calculate the risk of ships hitting bridges and coming up with construction standards so that new bridges would have a better chance of withstanding those collisions.
In the Sunshine Skyway collapse, the bulk carrier Summit Venture, registered in Liberia, got caught in high winds and heavy rain as it approached the bridge and rammed the western span of the bridge; when the roadway tumbled off its supports, 35 people fell to their deaths.
According to Knott, the problem has been looked at the wrong way: Bridge owners always blame mariners for hitting the bridge, but it’s the bridge that’s the obstacle to navigation. Engineers must build the bridge with the assumption that it will be struck. He even has a saying for this, called Knott’s Rule: “If you build it, they will hit it.”
Ship-bridge collisions have also increased worldwide because ships have become longer and wider over the years, and vessel traffic has increased. Older bridges are just not designed for these larger ships.
When it comes to protecting bridges, it’s not enough to shield piers next to the navigation channel; the entire bridge must be designed for a ship collision. The majority of ship-bridge collisions investigated by the NTSB involved an out-of-channel pier, according to Joe Osterman, the NTSB’s director of highway safety.
And it doesn’t take much force to bring a bridge down. “Barges are so massive that even a slow-velocity (collision) can create quite a bit of damage,” said Henry T. Bollmann, senior bridge designer for the Florida DOT.
In 1980, 35 people fell to their deaths after the bulk carrier Summit Venture struck the Sunshine Skyway Bridge in Tampa, Fla. The accident prompted significant changes in the way bridges are engineered. New bridges over navigable waterways are built with fenders or other design elements that help them withstand impacts from vessels.
Following studies of the problem, new engineering codes began to be instituted. Florida began designing bridges to withstand ship collisions starting in 1983, according to Bollmann. Louisiana adopted bridge-ship collision codes in 1985. And in 1991, the American Association of State Highway and Transportation Officials, an independent organization that sets many construction codes, adopted the first nationwide set of rules to design bridges to better withstand ship collisions. The 1991 specifications were voluntary, but in 1994, AASHTO made vessel collision a mandatory part of its overall bridge design specification.
In order to make bridges safer from ships, new bridges are designed with fewer piers in the water. Those piers are protected by fenders or artificial islands designed to ground a ship before it hits the pier. And every pier, even the ones outside the channel, is designed to withstand a minimum impact from a ship.
“It’s easy for bridge owners to blame the mariner, but the mariners are doing a good job,” Knott said. “Frankly, we would have a much greater problem on our hands but for the fact that we have such a skilled professional mariner community out there.”
A national group representing mariners recently began meeting with the U.S. Coast Guard to discuss bridge safety. A group from the American Waterways Operators is going over data on bridge collisions with the Coast Guard to see what improvements could be made, according to Anne Burns, a spokesperson for the AWO.
Which bridges are at risk?
Despite tremendous advances in bridge design and risk analysis, the major problem still remains: The country has no idea how many older bridges might collapse if hit by a ship.
It’s not for lack of effort on the part of the NTSB. After almost every major ship-bridge collision in the 1990s, the agency recommended that the FHWA conduct this type of survey.
In 1995, a task force with representatives from the Office of the Secretary of Transportation, the FHWA, the Coast Guard, the Federal Railway Administration and the Army Corps of Engineers adopted 10 risk factors to determine which bridges would be vulnerable to ship collision, according to NTSB documents.
In 1992 and 1994, the Coast Guard conducted a national bridge survey and found that 500 bridges needed better pier protection, navigation lights to reduce the risk of collisions, and emergency backup power for drawbridges, according to Nicholas Mpras, chief of the Coast Guard’s Office of Bridge Administration. Those improvements were made.
This was a one-time survey, Mpras said, noting that with a nationwide staff of 55, his office does not have the manpower to do bridge inspections on a regular basis. And his staff can’t check whether the bridge is vulnerable to collapse after a ship collision, because that’s an issue of structural integrity. “We have no statutory authority to do that,” he said.
But the FHWA did not believe that the national survey requested by the NTSB was necessary. “However, the FHWA believes the States currently have available for use the needed guidance for the performance of the recommended risk assessment,” wrote William A. Weseman, the FHWA’s director of the Office of Engineering, in a letter dated Nov. 15, 1995.
When asked if the recent bridge collapses in Oklahoma and Texas point to a need for a national assessment program, an FHWA spokesman said, “The most vulnerable bridges will need to be identified by the states, using the information contained in previous guidance … We can assure you that when vulnerable bridges are identified by the states and federal agencies that proper action is taken to mitigate the problems that are found.”
Nearly eight years after the NTSB’s first recommendation, the majority of states have not conducted a bridge-ship collision survey. In fact, states that go ahead and perform the work aren’t even required to inform the FHWA.
“Unfortunately, it usually takes a bridge collapse before a (state) DOT gets serious about it,” Knott said. “States that have never experienced this often act as if it can never happen here.”
Louisiana is one of the few states that has done a comprehensive survey. State highway officials looked at the state’s 200 major bridges over waterways and concluded that 56 needed to be more closely examined, according to Tony Ducote, a bridge engineer administrator for the Louisiana Department of Transportation and Development.
Two private companies were hired to do an in-depth analysis of each bridge. The total survey cost about $2 million, according to Ducote. Many of the bridges just needed small improvements, such as new lighting or new buoys in the waterways. The state decided that one bridge needed a $4 million retrofit to protect it from ships. As a result of the survey, some bridges were also moved higher up on the state’s replacement list.
The difficulty is that it can cost 50 percent or more of the original bridge’s cost just to renovate it for ship-bridge collisions, Ducote said. “That gives you an idea of the problems that the DOTs are faced with on this issue,” he said. But the survey was worth it. “We still feel that it gave us a tremendous advantage to identify these bridges,” he said. “Doing absolutely nothing is probably not the best course of action.”
Florida also does frequent surveys, although it’s not state policy, according to Bollmann. The state transportation department, working with the University of Florida, invented a computer program that helps engineers analyze bridges if the structures are hit by vessels. With that program and a copy of the bridge plans, Bollmann said he could do a risk analysis on a bridge in 10 days. And the state of Florida is now replacing the St. George’s Island bridge primarily because it was considered too big a risk for ship collision, he said.
Bridges in poor condition
Part of the problem is that so many of the nation’s bridges are in bad shape. About 28 percent of them were considered either structurally deficient or functionally obsolete as of December 2001, according to the FHWA. Although $3.5 billion a year is spent on bridges, there are still thousands of them that need replacement.
The NTSB is acutely aware of the problem. States “have a monumental task ahead of them to keep bridges from falling down of their own accord, much less from being hit by a waterborne force,” said Michelle McMurty, a project manager in the NTSB’s Office of Highway Safety. “We just want bridge risk assessment to be part of the picture.”
A further complication is that no one agency is responsible for bridges. Most are owned by state or county governments, which maintain the structures. The Coast Guard oversees all bridges, issues permits for new ones and regulates all navigation signals on and around them. The Army Corps of Engineers maintains many of the nation’s waterways.
“Bridge safety could be better if all the parties involved could talk to each other without all these jurisdictional boundaries,” Knott said.
Although a national survey would be difficult, it would not be unprecedented. Right now, the FHWA requires every state to check bridges over waterways for problems with scour, the erosion around bridge piers caused by the current. The program began after the 1987 collapse of the I-90 bridge over Schoharie Creek in New York state, which killed 10 people.
Engineers realize that every bridge at risk of collapse cannot be replaced. That would be much too expensive. “An assessment will at least allow you to prioritize the worst offenders — you can’t deal with all of them,” Knott said.
Another challenge may also be the difficulty our society has in making decisions about risk. When Knott does risk assessments of bridges, he can predict how many people would be killed if that bridge collapsed, and he attempts to assign a monetary value to those deaths. Clients ask him to keep that information out of his reports.
“We as a society are not ready to talk about risk in terms of lives being lost,” Knott said. “Politicians don’t want to talk about it, and engineers don’t want to talk about it, so we just keep it out.”