Series Is Presented Here As Two Variables--(1)--Original Data, 1921-1935 (2)--Original Data, 1935-1939 Source: Computed By NBER By Dividing Series (Net Ton-Miles) By Series (Aggregate Coal Consumption By Freight Steam Locomotive).
This NBER data series q03083 appears on the NBER website in Chapter 3 at http://www.nber.org/databases/macrohistory/contents/chapter03.html.
NBER Indicator: q03083
Release: NBER Macrohistory Database
National Bureau of Economic Research, Net Ton-Miles Per Pound of Fuel Consumed By Steam Locomotives In Freight Service for Great Britain [Q03083GBQ462NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/Q03083GBQ462NNBR, February 11, 2016.