Columbia subject headings:
Freight and freightage--United States.
Railroads--Freight--United States.
Railroads--United States--Freight.
Transportation and state--United States.
Trucking--United States.
Harvard subject headings:
Freight and freightage--United States
Railroads--Freight--United States
Transportation and state--United States.
Trucking--United States
Princeton subject headings:
Freight and freightage--United States.
Railroads--Freight--United States.
Transportation and state--United States.
Transportation, Automotive--United States--Freight.