United States. Bureau of Labor Statistics. "Railroads," in United States. Bureau of Labor Statistics. "April 1987," PPI Detailed Report (April 1987) : 147-149. https://fraser.stlouisfed.org/title/63/item/21617/toc/254237 , accessed on May 4, 2024.
United States. Bureau of Labor Statistics. "Railroads," in United States. Bureau of Labor Statistics. "April 1987," PPI Detailed Report (April 1987) : 147-149. https://fraser.stlouisfed.org/title/63/item/21617/toc/254237 , accessed on May 4, 2024.