They rely on half-century-old West German experiments on model ships for a key mathematical formula. Their minimum specifications cite the danger of empty 195-foot barges breaking loose from their moorings and drifting into bridges, a threat that seems quaint compared with the hulking 985-foot container ship that strayed off course after an electrical failure and
The U.S. bridge design specifications are developed and issued by the American Association of State Highway and Transportation Officials, or AASHTO. Federal regulation requires that bridge designers use them on national highways. Officials at the U.S. Department of Transportation consult on the standards, but don’t have a vote on what they include, which is set by the association of state officials.
It also noted that while U.S. design specifications do identify an empty hopper barge as a minimum “design vessel,” the specifications also require that bridges in deep-draft navigable waterways be designed for collisions with the size and speeds of ships expected to travel under them.. But doing so means broadening safety measures far beyond the bridges themselves and carefully coordinating different layers of safeguards, transportation experts said.
That has remained the case. And the lines of communication and responsibility were tested further after the Coast Guard was moved out of the U.S. Department of Transportation and into the new Department of Homeland Security, which opened in 2003.In Washington state, for example, the transportation department doesn’t track marine traffic under its bridges or how it has changed over time, Gaines said.
Some places have taken other steps to compensate for the vulnerability of their bridges. In New York Harbor, large container ships are guided by tugboats operated by trained captains, said Vincent Barone, press secretary for the New York City Department of Transportation. At its core is a formula for the “Annual Frequency of Collapse” — how often part of the bridge might be knocked down over the course of a year by a ship. The specifications say “critical or essential” bridges should withstand such dangers to a standard of one collapse per 10,000 years, the same as with the Danish span. The standard for “typical” bridges is one in 1,000 years.
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