Source: Data For 1920-1939: Ministry Of Transport, "Railway Statistics, " Successive Copies, January 1921-May 1939; Data For 1944-1952: NBER
This NBER data series q03078 appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: q03078
Release: NBER Macrohistory Database
National Bureau of Economic Research, Freight Train-Miles for Great Britain [Q03078GBQ456NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q03078GBQ456NNBR/, August 5, 2015.