Columbia subject headings:
Railroads--Capital productivity--United States--Congresses.
Railroads--Labor productivity--United States--Congresses.
Railroads--United States--Congresses.
Harvard subject headings:
Railroads--Capital productivity--United States
Railroads--Capital productivity--United States--Congresses
Railroads--Labor productivity--United States--Congresses.
Railroads--Labor productivity--United States.
Railroads--United States
Railroads--United States--Congresses
Princeton subject headings:
Railroads--United States--Capital productivity--Congresses.
Railroads--United States--Congresses.
Railroads--United States--Labor productivity--Congresses.