United States. Bureau of Labor Statistics. "Railroads," in United States. Bureau of Labor Statistics. "April 1988," PPI Detailed Report (April 1988) : 141-142. https://fraser.stlouisfed.org/title/63/item/21629/toc/416883 , accessed on May 9, 2024.
United States. Bureau of Labor Statistics. "Railroads," in United States. Bureau of Labor Statistics. "April 1988," PPI Detailed Report (April 1988) : 141-142. https://fraser.stlouisfed.org/title/63/item/21629/toc/416883 , accessed on May 9, 2024.