"The roughly 12,000-mile U.S. inland and intracoastal waterway system is an integral, albeit largely unnoticed, part of our nation's freight transportation system (see Figure 1). This network handles about 600 million tons, and 300 billion ton-miles, of domestic cargo movements annually -- principally raw materials and liquid and bulk primary products, like coal, petroleum, chemicals, grain, processed metals, cement, sand and gravel.1 It is the primary artery for more than half of the nation's grain and oilseed exports, for about 20 percent of the coal for utility plants, and for about 22 percent of domestic petroleum movements. From a national transportation perspective it is a 'quiet' mode, largely unnoticed by a general public used to dodging trucks on the highways or stopping for freight trains at suburban crossings. However, the infrastructure that supports this quiet mode is starting to show its age, and a major failure at one of its component locks and dams could have serious economic consequences that would give the quiet mode some very loud public attention."
Transportation Research Board: http://www.trb.org/