I grabbed the following information from the 2009 U.S. Census on average work commuting times. From the same chart, 86.1% drove a motor vehicle and 76.1% drove alone. Of those that commuted under 14 minutes, we find potentially 27.3% of all commuters could be considered short trippers. For a point of reference, my commute of a mile & 1/2 averages seven minutes.
Travel Time to Work - 2009 US Census
Less than 10 minutes 13.4%
10 to 14 minutes . 13.9%
15 to 19 minutes . 15.0%
20 to 24 minutes . 14.1%
25 to 29 minutes . 5.8%
30 to 34 minutes . 12.9%
35 to 44 minutes . 6.0%
45 to 59 minutes . 7.1%
60 to 89 minutes . 5.2%
90 or more minutes. 2.3%
Mean travel time to work (minutes). 25.1
www.census.gov/prod/2011pubs/acs-15.pdf