During Processing It Was Discovered That Monthly And Quarterly Figures For 1931 As Provided By NBER Do Not Agree, But Data Have Not Been Changed. The Annual Figure Provided Here Was Computed From Monthly Data. Source: Ministry Of Transport, Successive Issues Of "Railway Statistics"
This NBER data series m03080 appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: m03080
Release: NBER Macrohistory Database
National Bureau of Economic Research, Freight Train-Hours for Great Britain [M03080GBM568NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M03080GBM568NNBR/, November 25, 2015.