Series Is Presented Here As Two Variables--(1)--Original Data, 1920-1929 (2)--Original Data, 1929-1943 Source: NBER Derived This Variable By Dividing Series (Revenue Passenger-Miles) By Series (Passenger Train-Miles); Data Are From The Interstate Commerce Commission.
This NBER data series m03052a appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03052a
Release: NBER Macrohistory Database
National Bureau of Economic Research, Passenger-Miles Per Train-Mile, Class I Railroads for United States [M0352AUSM503NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M0352AUSM503NNBR, April 29, 2016.