Terrorists vs. Car Accidents

One of Matt Yglesias' readers looked up the statistics:

In the US, 583 billion passenger-miles were flown in 2008, the most recent year available (I think I can mix numbers from ’08 and ’09 without loss of generality). So if all that travel was done by car instead (obviously not feasible) with a fatality rate of 11.35 deaths per billion miles, we’d expect an increase of 6,617 deaths. In other words, terrorists would have to blow up 16 full 747′s a year (about one every three weeks) to make air travel as dangerous as car travel. I think that number gets at the point you were trying to make about the exaggerated scale of the threat of aviation terrorism.