1. U.S. Environmental Protection Agency. Sources of Greenhouse Gas Emissions. 2018. https://www.epa.gov/ghgemissions/sources-greenhouse-gas-emissions.
2. U.S. Department of Transportation. Bureau of Transportation Statistics. 2017 CFS Preliminary Data. U.S. Department of Transportation, 2018. https://www.bts.gov/surveys/commodity-flow-survey/2017-cfs-preliminary-data.
3. Freight Analysis Framework. FAF Trend -Over Time (1997-2045). 2012. https://explore.dot.gov/views/FAF_Dashboard_451/FAFTrend1997-2045?%0AiframeSizedToWindow=true&embed=y&showAppBanner=false&display_count=no&show%0AVizHome=no%0A}
4. Bureau of Transportation Statistics. National Transportation Statistics 9/4/19 Update, Shares of U.S. Energy Consumption and Other Categories. 2019. https://www.bts.gov/newsroom/national-transportation-statistics-9419-update-shares-us-energy-consumption-and-other.