Driving fatalities after 9/11: a hidden cost of terrorism

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 11 September 2001 terrorist attacks, events that prompted many travellers to substitute road transportation for safer air transportation. After controlling for time trends, weather, road conditions and other factors, we find that travellers' response to 9/11 resulted in 327 driving deaths per month in late 2001. Moreover, while the effect of 9/11 weakened over time, as many as 2300 driving deaths may be attributable to the attacks.