United States. Bureau of Labor Statistics and Johnson, Richard N. Railroad Technology and Manpower in the 1970's : Bulletin of the United States Bureau of Labor Statistics, No. 1717 , Washington, D.C: For sale by the Supt. of Docs., U.S. Govt. Print. Off., 1972, https://fraser.stlouisfed.org/title/4830, accessed on September 12, 2024.