|Total trips*||SE||Total miles**||SE|
|All person trips||411||1.9||4,012||44.9|
|Person trips by personal vehicle||356||1.9||3,552||41.3|
* In order to correctly calculate miles per trip, denominators of 403, 350, and 233 billion trips were used for all person trips, personal vehicle person trips, and vehicle trips respectively because not all cases had reported mile values associated with them.
** The total mileage is an undercount as it does not include vehicle mileage from non-daily long distance trips, trips that form part of a job other than commuting e.g. taxi cab driving, and due to nonresponse on trip mileage.
NOTE: SE = standard error.
SOURCE: The 2001 National Household Travel Survey, daily trip file, U.S. Department of Transportation.