Data Refer To Aaa Grade Bonds. Source: Moody'S Transportation Manual, 1965; Moody'S Bond Survey, Weekly Issues Thereafter.
This NBER data series m13061 appears on the NBER website in Chapter 13 at http://www.nber.org/databases/macrohistory/contents/chapter13.html.
NBER Indicator: m13061
Release: NBER Macrohistory Database
National Bureau of Economic Research, Yields On Railroad Bonds, Highest Rating for United States [M13061USM156NNBR], retrieved from FRED, Federal Reserve Bank of St. Louis https://research.stlouisfed.org/fred2/series/M13061USM156NNBR/, October 4, 2015.