United States. Bureau of Labor Statistics. "Union Wages and Hours: Motortruck Drivers and Helpers, July 1, 1968 : Bulletin of the United States Bureau of Labor Statistics, No. 1622," Union Wages and Hours : Local Truckdrivers and Helpers (1969). https://fraser.stlouisfed.org/title/3960/item/498443, accessed on May 15, 2025.