Pandemic Flu Could Clog U.S. Rail Lines

A simulation by systems engineers shows rail network is sensitive to pandemic flu, but port system is more robust

PHOTO: Landov

30 April 2009—A moderate level of absenteeism due to a pandemic flu outbreak could cause widespread problems in the U.S. rail freight network, according to research presented last year at the Hawaii International Conference on System Sciences. However, even a severe outbreak is unlikely to jam up the nation’s ports.

Systems engineers at Cornell University and Sandia National Laboratories analyzed the impact of influenza at three levels of severity. In the midlevel scenario, in which absenteeism peaks at 13.6 percent during an outbreak, the effective capacity of the United States’ 18 major rail yards is cut by 10 percent. That might not seem like much, but there is so little spare capacity in the rail system that such a pandemic would lead to widespread problems lasting six to eight weeks.

The lightest-impact scenario analyzed, a 5.8 percent peak absenteeism, could lead to increased congestion and one- to three-day shipment delays, but it was nothing the rail system couldn’t handle. However, in the worst scenario, with an absentee peak of 28.2 percent, demand at the major rail yards would exceed capacity by 60 to 70 percent, completely clogging the system with stalled shipments.

”We have a very brittle system already in rail,” says Linda K. Nozick, a professor of systems engineering at Cornell University, who was part of the team that performed the simulation. The main problem is with the nation’s 18 major rail yards. In February 2007, the time period the researchers used as a base, freight cars spent just over 28 hours on average at each yard they passed through. At the yards, trains are taken apart, inspected, and assembled to route freight around the network. ”There’s a lot of demand at these yards and not a lot of resources,” Nozick says.

Pandemic influenza’s potential influence on the U.S. port system should be considerably less, because the ports have some spare capacity, Nozick and her colleagues found.

”On the surface, I thought we’d have more problems at the ports,” says Nozick. ”But the calculations don’t bear it out.”

The three largest ports in the United States—Los Angeles, Long Beach, and New York–New Jersey—handle a whopping 50 percent of the entire country’s container traffic. The researchers focused on the Port of Los Angeles because of its similarity to the other two ports, finding that only one of its eight terminals would run into big trouble even under the 28.2 percent absentee scenario. However, Nozick notes, their analysis did not examine what happens beyond the dock boundaries, such as in the container yards.

The engineers decided to study flu’s effects on rail and port systems because they figured that the impact there would be greatest. Demand for passenger travel by air, rail, and bus would probably diminish quickly, as it did during the SARS pandemic in 2003. ”But when you talk about freight, people need food and other goods,” Nozick says. ”In many urban areas, there is, in fact, very little extra supply out there.”

The interdependency of infrastructure networks, such as the rail system and the ports, has been a topic of great research interest, says Nozick. It was just such an interdependency that led to a serious shipping backup off the coast of Los Angeles in 2004. The ultimate cause was a lack of trained workers at one of the three railroads that carry 40 percent of all the containers away from the ports of Los Angeles and Long Beach. The delays in the rail yard spilled into the ports’ container storage area and then spread as far away as ships at sea.

”Understanding how transportation networks behave under stress is important,” says Nozick. ”Pandemic influenza is just one stress.”

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