1935-1943 Midmonth Figures Were Averaged By NBER From Published End Of Month Data. Source: Interstate Commerce Commission, Freight And Passenger Service Operating Statistics, Statement M210 And Icc, Motive Power And Car Equipment.
This NBER data series m01267 appears on the NBER website in Chapter 1 at http://www.nber.org/databases/macrohistory/contents/chapter01.html.
NBER Indicator: m01267
Release: NBER Macrohistory Database
National Bureau of Economic Research, Freight Service, Cars Owned for United States [M01267USM543NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M01267USM543NNBR/, October 9, 2015.