Series Is Presented Here As Two Variables--(1)--Original Data, 1920-1935 (2)--Original Data, 1935-1943 Switching And Terminal Companies Are Excluded Throughout. Beginning In 1935, Coverage Excludes "1/2 Combination" And "Observation" Passenger Car-Miles. Source: Interstate Commerce Commission, "Revenue Traffic Statistics Of Class I Steam Railways In The United States".
This NBER data series m03059b appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03059b
Release: NBER Macrohistory Database
National Bureau of Economic Research, Passenger-Miles Per Car-Mile, Class I Railroads for United States [M0359BUSM503NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M0359BUSM503NNBR/, August 2, 2015.