Overall and modal trade totals cited here are based on annual data reported by the Foreign Trade Division of the U.S. Census Bureau in the FT920 U.S. Merchandise Trade: Selected Highlights, (December 1999) report, U.S. Exports of Merchandise CD (December 1999), and U.S. Imports of Merchandise CD (December 1999). Following the release of these products, the Census Bureau also makes available (on an annual basis) revised overall and country totals. These revised figures are used by Census and other federal agencies.
Due to the way U.S. international trade data has historically been collected and processed, accurately calculating the modal share of that trade for all modes of transportation (including disaggregated land modes) was not possible until 1997. Because of this difficulty, the mode of transportation data are not corrected in the revised figures provided by the Census Bureau. Therefore, this section relies on both the overall and mode of transportation data in the originally documented merchandise trade figures as cited in the report and CDs mentioned above.