|Number of U.S. airports|
NOTE: 298C (small carriers) and commuter carriers began reporting in 2002. See glossary for definition of small carriers. U.S. airports include those in the U.S., Puerto Rico, and the U.S. Virgin Islands.
Prior to 2000 and after 2007 air traffic hubs are designated as geographical areas based on the percentage of total passengers enplaned in the area. Under this designation, a hub may have more than one airport in it. (This definition of hub should not be confused with the definition used by the airlines in describing their "hub-and-spoke" route structures). Individual communities fall into four hub classifications as determined by each community's percentage of total enplaned revenue passengers in all services and all operations of U.S. certificated route carriers within the 50 states, the District of Columbia, and other U.S. areas. For 2000-2006, hub designation is based on passenger boarding's at individual airports as designated by the FAA. Classifications are based on the percentage of total enplaned revenue passengers for each year according to the following: Large = 1 percent or more, Medium = 0.25 to 0.9999 percent, Small = 0.05 to 0.249 percent, Nonhub = less than 0.05
SOURCE: U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, Office of Airline Information, T100-Segment Database, special tabulation, July 2010.