|Major air carriers||11||12||13||13||13||15||15||15||14||14||17|
|Other air carriers||85||84||83||83||81||76||72||68||66||69||68|
|Class I railroads||11||10||9||9||9||8||8||7||7||7||7|
|Interstate motor carriers||346,000||379,000||417,000||477,486||517,297||560,393||592,909||600,104||674,314||677,317||679,744|
|Marine vessel operators||1,381||1,348||1,311||1,235||1,174||1,114||1,063||877||798||767||773|
|Hazardous gas transmission||217||225||237||243||239||237||232||222||235||275||292|
|Natural gas transmission||975||971||957||889||885||844||816||900||925||913||945|
|Natural gas distribution||1,444||1,397||1,365||1,375||1,393||1,363||1,341||1,331||1,309||1,318||1,291|
NOTES: Air carrier groups are categorized based on their annual operating revenues as major, national, large regional, and medium regional. The thresholds were last adjusted July 1, 1999, and the threshold for major air carriers is currently $1 billion. The other air carrier category contains all national, large regional, and medium regional air carriers. Interstate motor carrier figures are for the fiscal year, October through September. The Federal Motor Carrier Safety Administration deletes motor carriers from the Motor Carrier Management Information System (MCMIS) when they receive an official notice of a change in status. This most often occurs when a safety audit or compliance review is attempted. As a result, inactive carriers may be included in the MCMIS. There is some overlap among the operators for the pipeline modes so the total number of pipeline operators is lower than the sum for the three pipeline modes.
SOURCES: Various sources, as cited in U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, National Transportation Statistics 2007, table 1-2, available at http://www.bts.gov/, as of April 2007.