Daily Averages Are Used Through January 1935. Thereafter, Midmonth Figures Were Computed Based On End Of Month Data. New York Central Figures Are Not Available, 02-12/1920; Missouri-Pacific Figures Are Not Available, 02-03/1920; Fort Smith And Western Are Not Available, 03/1920. Beginning With 1935, Data Were Computed By NBER By Summing "Number Serviceable (Not Stored)" And "Number Serviceable (Stored)." Switching And Terminal Companies Are Excluded Through December 1936. They Are Included Thereafter Beginning In February 1937. The January 1937 Figure Is The Average Of The 12/1936 And 02/1937 Figures. Source: 1920-1934 Data Are From Interstate Commerce Commission, Freight And Passenger Service Operating Statistics Of Class I Steam Railways In The United States; 1935-1943 Data Are From Icc, Motive Power And Car Equipment Of Class I Steam Railways In The United States.
This NBER data series m01251 appears on the NBER website in Chapter 1 at http://www.nber.org/databases/macrohistory/contents/chapter01.html.
NBER Indicator: m01251
Release: NBER Macrohistory Database
National Bureau of Economic Research, Serviceable Locomotives Assigned To Freight Service, Class I Railroads for United States [M01251USM481NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M01251USM481NNBR/, July 29, 2015.