Fear of Flying?

“Flying and Driving after the September 11 Attacks” by Michael Sivak and Michael J. Flannagan, in American Scientist (Jan.–Feb. 2003), P.O. Box 13975, Research Triangle Park, N.C. 27709–3975.

After the terrorist attacks of September 11, 2001, many travelers decided it would be safer to drive to their destinations than to fly. Not a good choice, it turns out.

Driving becomes more dangerous as the miles traveled mount, note Sivak and Flannagan, researchers at the University of Michigan Transportation Research Institute. The risk in flying, in contrast, increases mainly with the number of takeoffs and landings. Out of 7,071 airline fatalities worldwide between 1991 and 2000, 95 percent occurred either during takeoff and ascent or during descent and landing.

Using U.S. National Transportation Safety Board data on domestic flights (including the four in which 232 passengers lost their lives on September 11), the two researchers calculate that the risk of death for airline passengers was about 78.6 in one billion per nonstop segment traveled. (The risk roughly doubles when an intermediate stop is added, triples with two such stops, and so on.)

To gauge the risk in driving, the researchers looked at traffic deaths on the very safest roads in America, its rural interstate highways. The resulting risk of death: 4.4 in one billion per kilometer traveled.

That means, the authors calculate, that one would have to drive only about 18 kilometers (or 11.2 miles) to equal the risk of flying one nonstop segment on an airliner.

What if September 11 has ushered in a new era of terror in the skies? “For flying to become as risky as driving” during the 10-year period they studied, the authors write, “disastrous airline incidents on the scale of those of September 11th would have had to occur about once a month.”