Well-renowned security expert Bruce Schneier claims that

In the months after 9/11, so many people chose to drive instead of fly that the resulting deaths dwarfed the deaths from the terrorist attack itself, because cars are much more dangerous than airplanes.

Our Newfound Fear of Risk

Is this backed up by hard data anywhere?

  • 2
    en.wikipedia.org/wiki/Micromort It's much more risky to travel by car than by plane. 1 micromort is 340 miles with car, and 1000 miles with plane. I can maybe dig up statistics on dying per trip too, plane vs car.
    – Wertilq
    Sep 3, 2013 at 16:58
  • @Wertilq That Wikipedia page lists 230 miles in a car per micromort.
    – Ladadadada
    Sep 3, 2013 at 17:16
  • Hm. How uncharacteristic for Bruce to not back up a substantial claim like this. I’ve sent him a tweet asking for clarifications. Sep 4, 2013 at 7:14
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    He clarified now that it should have been years instead of months (schneier.com/blog/archives/2013/09/excess_automobi.html). He also added some sources for the claim in this later post.
    – Mad Scientist
    Sep 9, 2013 at 12:58

1 Answer 1



According to a 2005 report from National Highway Traffic Safety Administration (NHTSA):

Table 1

The number of billions of miles driven and the number of fatalities on US roads increased slowly [data from Table 1 and Table 2]:

  • 2000: 41,945 fatalities over 2,747 billion miles.
  • 2001: 42,196 fatalities over 2,797 billion miles.
  • 2002: 43,005 fatalities over 2,856 billion miles.

Even if the entire increase in fatalities could be attributed to increased driving due to the fear/unavailability of flying, and the entire increase in 2001 was September or later, that is "only" an increase of 1,311 fatalities over a period of 15 months.

Compare that to the number of casualties in the 9/11 attacks which is generally placed just shy of 3,000.

Examining the graph, the trend for increasing fatalities extends further back than 2001. Even as fatality rates per mile travelled has improved, the distances travelled has increased.

To convince myself there wasn't a spike in the distance travelled data that i wasn't seeing in the column of numbers, I plotted it:

Graph of distance travelled

I didn't perform any advanced statistical analysis on this - it was sufficient to persuade me that there was no noticeable spike after 2001.

  • 5
    Its probably impossible to measure how many would have not driven had 9/11 not happened, so there's no real baseline. The original claim is getting into the question of driver motive which is pretty murky. Sep 3, 2013 at 18:54
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    Another potential problem with this data: Bruce mentions that the increase happened in the months after 9/11, so maybe this data representation isn’t fine-grained enough. I personally don’t think so though. Sep 4, 2013 at 7:17
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    @Konrad: If there was a spike in early 2002 that was subsumed by an equivalent dip in late 2002, your suggestion would make sense, but seems highly unlikely.
    – Oddthinking
    Sep 4, 2013 at 9:15
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    Bruce has now written a blog entry about this statement: schneier.com/blog/archives/2013/09/excess_automobi.html
    – Perseids
    Sep 9, 2013 at 12:33
  • 4
    Great to see Schneier defending his position with references. I note that no less than Gigerenzer has drawn the opposite conclusion from me, which drastically reduces my faith in my answer. I haven't had a chance to go through the details though. I encourage someone to put up a counter-argument based on Schneier's references, ripping my argument to shreds. Seriously, (politely) show me I am wrong, and I will delete this answer both cheerfully and contritely (if that is a possible combination).
    – Oddthinking
    Sep 9, 2013 at 13:22

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