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A Statistical Study of Commodity Freight Value/Tonnage Trends in the United States

The last two decades have seen dramatic economic, technical and market changes in the United States including widespread internet adoption, rapid advances in information and communication technologies, outsourcing, and the globalization of supply chains. These changes are likely affecting the demand for freight transportation as well as the type and prominence products shipped by commodity group. This research focuses on the study of value/tonnage trends for some key commodities. Value/tonnage ratios are not only relevant because they can show aggregate trends for key commodity groups but also because they are utilized in many freight models at the freight generation stage. Statistical results indicate that some changes in value/tonnage ratios are statistically significant. Implications of these results for freight modeling efforts are discussed.