United States. Bureau of Labor Statistics. "Railroads," in United States. Bureau of Labor Statistics. "May 1987," PPI Detailed Report (May 1987) : 135-137. https://fraser.stlouisfed.org/title/63/item/21618/toc/132873 , accessed on March 29, 2024.
United States. Bureau of Labor Statistics. "Railroads," in United States. Bureau of Labor Statistics. "May 1987," PPI Detailed Report (May 1987) : 135-137. https://fraser.stlouisfed.org/title/63/item/21618/toc/132873 , accessed on March 29, 2024.