The volume of freight carried by railroads increased 26 percent (in tons) and 30 percent (by carload) on railcars between 1991 and 2001 (figure 22). However, on average, the weight of each railcar remained fairly constant. The average weight of a loaded railcar ranged from 63 to 67 tons during the same period (figure 23).
The relatively steady average weight of a loaded railcar masks countervailing trends among selected freight commodities. The average weight of a carload of coal, which represented 46 percent of rail freight tonnage in 2001, was 110 tons in 2001, up from 99 tons in 1991 (figure 24). Farm products, food and kindred products, nonmetallic minerals, and chemicals and allied products, which together represented 29 percent of tonnage in 2001, were also shipped in heavier average carloads in 2001 than in 1991 .
Miscellaneous mixed shipments is the only category of goods that was transported in lighter average carloads . Miscellaneous mixed shipments are primarily intermodal freight composed of shipping containers on flatbed railcars . The containers, which are primarily used to move manufactured goods that tend to be lighter and more valuable than raw materials, may be transported by waterborne vessel and truck, as well. Miscellaneous mixed shipments increased by 54 percent in terms of tonnage and by 79 percent in terms of carloads between 1991 and 2001, resulting in carloads that were 14 percent lighter in 2001 .
1. Association of American Railroads, Railroad Facts 2001 and 2002 (Washington, DC: 2001 and 2002).
2. Calculations based on Association of American Railroads, Railroad Ten-Year Trends, 1990–1999 (Washington, DC: 2000).