Series Is Presented Here As Two Variables--(1)--Original Data, 1920-1929 (2)--Original Data, 1929-1943 Data Exclude Switching And Terminal Companies. Source: Interstate Commerce Commission, "Freight And Passenger Service Operating Statistics Of Class I Steam Railways In The United States."
This NBER data series m03051a appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03051a
Release: NBER Macrohistory Database
National Bureau of Economic Research, Passenger Train-Miles, Class I Railroads for United States [M0351AUSM456NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M0351AUSM456NNBR, February 8, 2016.