Q. Number of Large Trucks and Trucking Companies
You can find the number of registered large trucks by adding the categories "Single-Unit 2-Axle 6-Tire or More Trucks" and "Combination Trucks" in the Federal Highway Administration's Highway Statistics, Table VM-1: http://www.fhwa.dot.gov/policyinformation/statistics/2010/vm1.cfm. This table also includes information on fuel consumption and vehicle miles of travel.
Statistics on the number of truck and truck tractor registrations are also available in Highway Statistics, table MV-9: http://www.fhwa.dot.gov/policyinformation/statistics/2010/mv9.cfm.
Statistics on the number of semi-trailer registrations can be found in table MV-11 of the same source: http://www.fhwa.dot.gov/policyinformation/statistics/2010/mv11.cfm.
For previous editions of Highway Statistics, please see: http://www.fhwa.dot.gov/policyinformation/statistics.cfm
The Federal Motor Carrier Safety Administration has the number of active carriers with US DOT Numbers at: http://ai.fmcsa.dot.gov/International/border.asp?redirect=GenStats.asp. Although you cannot obtain the number of trucking companies, you can obtain the number of non-passenger carriers by subtracting the number of passenger carriers from the total number of carriers.
For additional trucking statistics, you may want to contact the American Trucking Associations: http://www.truckline.com/Pages/Home.aspx
(Note: This private-sector site and/or company is not necessarily recommended, maintained, or endorsed by the US DOT or any US Government office. We offer this suggestion strictly as a convenience, should you be interested in exploring their services)