We show that the public's response to terrorist threats can have unintended consequences that rival the attacks themselves in severity. Driving fatalities increased significantly after the September 11, 2001 terrorist attacks, events that prompted many travelers to substitute road transportation for safer air transportation. After controlling for time trends, weather, road conditions, and other factors, we find that travelers' response to the attacks resulted in 344 driving deaths per month in late 2001. Moreover, while the effect of the attacks weakened over time, a total of about 2,170 driving deaths may be attributable to the attacks.

Work began in 2004 based on press reports of increased driving fatalities. Recent attacks and threats to public transporation systems in New York City, London, and Madrid generalize the problem: the response to attacks and threats can have unintended consequences that should be considered by policy makers.

The paper is currently under review. A working version is posted on the Social Science Research Network.

The white paper version was the topic of a short piece on News 10 Now, a Central New York news show on the Time Warner Cable network. Our work has also been cited in The Week, Fortune, Reuters wire service, the International Herald Tribune, and the Washington Post.

• Garrick Blalock
• Daniel H. Simon
• Vrinda Kadiyali