BOX 1. Selecting the Leading Gateways

This report ranks freight gateways by the value of merchandise trade they handle. Value data were compiled from multiple sources, allowing comparison of all the freight modes. See box 2 for a detailed description of the freight data sources.

The relative position of the top gateways would be different if ranked by weight because, for example, seaports handle heavier or bulkier goods than airports. This report ranks by value because export weight data are incomplete in data collected by U.S. authorities. Tonnage data are available for imports and exports by air and water modes. For land modes (truck, rail, and pipeline), tonnage data are only collected for imports. U.S. exporters are not required to report export weight.

Where export and import tonnage data are both available (e.g., for seaports and airports), this report presents the weight data without making a comparison with land gateways. The report also identifies import tonnage at land gateways.

It is possible to estimate export tonnage using value-to-weight ratios derived from imported commodities. The accuracy of such estimates is likely to be greater at the national level than at the gateway level. Therefore, weight data for land exports have not been estimated for individual gateways. However, BTS has estimated the weight of land exports at the national level, and this information is presented in figure 3.

SOURCE: U.S. Department of Transportation, Research and Innovative Technology Administration, Bureau of Transportation Statistics, November 2009.