Series Is Presented Here As Twor Variables--(1)--Original Data, 1907-1925 (2)--Original Data, 1920-1956. Data Were Computed By NBER By Dividing Series 03016B (Freight Operating Revenues, Class I, Excluding Switching And Terminal Companies) By Series 03003 (Revenue Ton-Miles, Class I, Excluding Switching And Terminal Companies); Both Series Are Based On The Interstate Commerce Commission Source. Source: NBER Computed Data From Interstate Commerce Commission, "Revenue Traffic Statistics Of Class I Steam Railways In The United States".
This NBER data series m03003ac appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03003ac
Release: NBER Macrohistory Database
National Bureau of Economic Research, Revenue Per Freight Ton-Mile, Class I Railroads for United States [M033ACUSM270NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M033ACUSM270NNBR/, December 1, 2015.