These Data Were Computed By NBER From Figures Given In The Sources. Switching And Terminal Companies Are Included For 1917-1931. Source: Interstate Commerce Commission"Operating Revenues And Expenses Of Large Steam Roads In The U.S.: July, 1914 To December, 1919" For 1917-1919 Data; "Operating Revenues And Operating Expenses Of Class I Steam Railways In The U.S." For 1920-1942 Data (See Note Below).
This NBER data series m09047 appears on the NBER website in Chapter 9 at http://www.nber.org/databases/macrohistory/contents/chapter09.html.
NBER Indicator: m09047
Release: NBER Macrohistory Database
National Bureau of Economic Research, Ratio of Net Railroad Operating Income To Total Operating Revenues, Class I Railroads for United States [M09047USM156NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M09047USM156NNBR/, July 30, 2015.