The geography of freight flows by mode is determined, for the most part, by the distribution of population and industry and availability of transportation infrastructure. The effect of transportation infrastructure is especially pronounced with waterborne shipments, which rely on inland waterways, including the Great Lakes and the Mississippi River system, and coastal ports (figure 1-14). Some of the leaders in waterborne shipments, for instance California and Washington, are states with large coastal ports. Others, such as West Virginia and Indiana, ship or receive large amounts of freight via the inland waterway system. Some, like Louisiana, ship and receive freight through coastal ports and the inland waterway system.
With the ubiquity of the highway network, the amount of freight moving to and from each state by truck is closely related to population size (figure 1-15). Thus, 8 of the 10 most populated states (California, Florida, Georgia , Illinois, Michigan, Ohio, Pennsylvania, and Texas) are leaders in both inbound and outbound truck shipments.
States producing or consuming large amounts of coal are often the leaders in shipments of goods originating or terminating by rail (figure 1-16). For instance, Wyoming, West Virginia, Kentucky, and Pennsylvania are the four largest producers of coal in the United States. Coal shipments to Georgia , Missouri, Indiana, Wisconsin, and Ohio place these states among the leaders of inbound rail shipments. However, the top commodity originating and terminating in California by rail is mixed freight and the top commodity originating in Minnesota is metallic ores. Texas leads in both inbound and outbound chemical shipments .
The amount of inbound and outbound shipments by air, like trucking, is closely related to state population (figure 1-17). A major exception is Hawaii, which, as an island state, is a leader in inbound air freight shipments despite its relatively low population. The Commodity Flow Survey,1 the source of the data for trucking and air shipments, captures the state origin and destination of shipments but not in-transit shipments. Hence, states with airports that are major air freight sorting and distribution facilities, such as the FedEx facility in Memphis, Tennessee, may not register as leaders.
1. Association of American Railroads, Railroads and States 2002 (Washington, DC: 2004).
1 See Commercial Freight Activity, especially box 1-C.