Data Exclude Switching And Terminal Companies. The Unadjusted Figure For January 1920 Was Computed By Subtracting The Known February Figure From A Two-Month Cumulative Total. Source: Interstate Commerce Commission, Data For 1920-1934: "Freight And Passenger Service Operating Statistics Of Class I Steam Railways In The United States"; Data For 1935-1943: "Freight Train Performance Of Class I Steam Railways In The United States"
This NBER data series m03045 appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03045
Release: NBER Macrohistory Database
National Bureau of Economic Research, Freight Train-Miles, Class I Railroads for United States [M03045USM456NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M03045USM456NNBR/, August 4, 2015.