According to the NTSB 32367 is the estimated number of highway related fatalities recorded by the US department of trans­porta­tion during 2011. 11981 (that is 37%) of those 32367 fatalities were due to incidents involving passenger cards.

For reference the estimated number of aviation related fatalities for the same period was 494. Ad­di­tion­al­ly, 0 of those aviation fatalities occurred on airlines (i.e. most of the fatalities occurred due to incidents involving private planes).

Finally, what about the number of deaths of US citizens worldwide due to terrorism? According to the US Department of State: 17. Obviously this figure does not include military deaths–see the linked page for a precise definition of US citizen fatalities due to terrorism.