Flying within the United States remains a much safer way to travel than driving, even when accounting for airline fatalities resulting from the terrorist attacks on Sept. 11, 2001. According to a new analysis of transportation safety, the average nonstop flight in the United States spans roughly 1,150 kilometers, and the risk of death from driving that distance is about 65 times that from flying.
Most risk from air travel is associated with takeoffs and landings, says Michael Sivak, a psychologist at the University of Michigan Transportation Research Institute in Ann Arbor. Worldwide, about 95 percent of airline fatalities between 1991 and 2001 occurred during those phases of flight, so the risk of flying doesn’t depend for the most part on the distance traveled.
Sivak and his institute colleague Michael J. Flannagan estimated the risk of air travel in the United States by analyzing data collected from 1992 through 2001.
During that period, the 10 largest U.S. air carriers’ nonstop domestic flights–excluding commuter flights–transported more than 5.5 billion passengers. Of those travelers, 433 died, including the 232 passengers on the ill-fated 9/11 flights. Therefore, the researchers calculate that the risk of death for any particular passenger for each nonstop domestic flight was less than 1 in 10 million. That’s about 1 fatality per 15 billion km traveled.
The researchers analyzed data from a 10-year period because the annual number of airline fatalities varies widely. There weren’t any deaths on commercial flights within the United States in 1993, 1998, or 2002, says Paul Takemoto of the Federal Aviation Administration in Washington, D.C.
Someone who was afraid to fly would probably drive to his or her U.S. destination via interstate highways, says Sivak. Unlike air travel, highway driving has its risk almost evenly distributed throughout the trip. For the year 2000–the most recent year for which detailed statistics are available–there were 1,511 driver fatalities involving cars, light trucks, vans, and sport utility vehicles on intercity stretches of interstate highways. Those vehicles tallied about 345 billion km on those roads that year, says Sivak. Therefore, the risk of death while driving long distances via interstate highways–the safest driving environment, the researchers note–was a little over 4 per billion for each kilometer traveled.
From the two risk estimates, the researchers calculated a parameter called the indifference distance, the distance for which the two modes of transportation are equally risky. For the new analysis, the indifference distance is about 18 km. In other words, driving on even the safest roads is riskier than flying any distance where commercial air travel is an option, says Sivak. He and Flannagan report their analysis in the January/February issue of American Scientist.
Earlier studies have also shown that the risk of injury or death when traveling significant distances is greater in a car than it is in an aircraft, says Roger Blackman, a psychologist at Simon Fraser University in Burnaby, British Columbia. “In fact, for most people, the most dangerous part of air travel is their trip by car to the airport,” he notes.
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