Source: Commerce And Labour Dept.
This NBER data series a02084da appears on the NBER website in Chapter 2 at http://www.nber.org/databases/macrohistory/contents/chapter02.html.
NBER Indicator: a02084da
Release: NBER Macrohistory Database
National Bureau of Economic Research, Mileage of New Railway Lines Authorized By Parliament for Great Britain [A024DAGBA374NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/A024DAGBA374NNBR/, August 2, 2015.