US Waterborne Freight
1) Anyone who ships cargo would be interested in this statistic. This could include not only people who ship cargo by water, but people who ship cargo by air or land, because they may be interested in changing their method of shipment. Government officials who are in charge of regulating waterborne freight or ensuring border security would also be interested in this statistic. Also, workers in any type of shipping industry, or those hoping for employment in a shipping industry, would be interested in US waterborne freight statistics.
2) This information is collected by the Army Corp of Engineers Navigation Data Center. Data on “waterborne commerce” appears to have been collected every five years starting in 1960 and then every year starting in 1990, but ending in 2008.
3) The most recent statistic for “US Waterborne Freight” in general (rather than for internal US waterways only) is from 2008, when the total amount of US Waterborne Freight was 2,469.8 million short tons. This level of freight is over double the amount in 1960 (1099.9 million short tons). Since 1960 there has been a general trend of a continuing increase in freight amount. This trend, however, is not steady (it does not make a perfectly increasing line), with increases or decreases of up to 200 million short tons from year to year.
Data summarized by the Research and Innovative Technology Administration (RITA) Bureau of Transportation Statistics, under Publications > National Transportation Statistics: http://www.bts.gov/publications/national_transportation_statistics/html/table_01_50.html
The Bureau of Transportation Statistics webpage linked to US Army Corp of Engineers Navigation Data Center where the data was originally published: http://www.ndc.iwr.usace.army.mil/wcsc/wcsc.htm