Here are the most understandable statistics I've seen to date that compare the risks of flying and driving. Remember that almost all of the danger in flying comes during take-off and landing, so the length of the flight isn't very important.
In terms of time, at 55 MPH, 11 minutes 47 seconds of driving [10.8 miles] equals the risk of taking a flight. Since the average airline trip is 694 miles and takes about an hour and a half, 11 minutes 47 seconds of driving has the same risk of fatality as the average airline flight. But it also means that 11 minutes 47 seconds of driving equals flying eight hours to Europe or flying fourteen hours to the Orient.
Don't forget that these stats involve rural Interstate driving. If flying were compared with driving on urban or suburban roads and streets, a trip of just one to two miles would be equal in risk to one flight. This means the risk you face every two to four minutes of non-interstate driving equals the risk of one flight. ...
Notice that these figures INCLUDE the fatalities of the passengers on the hijacked 9/11 flights. What if terrorism increases? How much would terrorist have to increase for flying to become as risky as driving? Sivak and Flannagan figure disastrous airline incidents on the scale of those of September 11th would have to occur 120 times over a 10-year period, or about once a month for flying to become as risky as rural interstate driving.
Flying is probably scarier because we do it more rarely and we're not in control of the plane outselves. People are terrible assessors of risk.