Q. Number of Truck/Bus Drivers in the US
Statistics on the number of commercial drivers can be found in the "FMCSA Pocket Guide to Large Truck and Bus Statistics" at this site.
More trucking-related statistics can be found on the "Data, Analysis and Statistics" site at http://www.fmcsa.dot.gov/facts-research/facts-figures/analysis-statistics/dashome.htm
Additional motor vehicle facts can be found on the FMCSA A&I Research web site.
See also the Bureau of Labor Statisticsfor employment statistics.