In the weeks after the attacks of September 11, 2001, many thousands of Americans took to the roads and highways in lieu of flight. Some opted to drive because their vacation or business air travel was cancelled; others because they were understandably afraid of subsequent hijackings. Some years later, a group of Cornell University economists determined that after the terror attacks, in the last three months of [2001] fear of flying revved up car use and caused a second toll of lives in US roads. In addition, the inconvenience of tighter airport security after 9/11 may have further encouraged substitution...