Technical documentation 6-2c: U.S. Merchandise Trade With Canada and Mexico by Mode of Transportation (Thousands of metric tons)

Shipping weight: Shipping weight represents the gross weight in kilograms of shipments, including the weight of commodities and packaging (such as wrappings, crates, boxes and containers). For air, maritime vessel and imports by land modes of transportation, shipping weight information is a required data element on the merchandise trade documents of the Departments of Commerce and Treasury. Currently, data on the shipping weight of exports by land modes of transportation (truck, rail, pipeline, mail and other) are not required to be collected if the exporter or broker files paper trade documentation, known as the Shipper's Export Declaration. (At present, approximately 30-40 percent of U.S. export data are collected via paper trade documents). Under new automated filing procedures through the Automated Export System (AES), shipping weight for exports will be required. Although AES is available at all ports, quality export weight data is not available because not all shipments are reported with the system. BTS estimates surface export weight using the value-to-weight ratios for imports by country and mode of transportation.

The TransBorder database provides value of U.S. exports to, and value and weight of U.S. imports from Canada and Mexico for surface modes (truck, rail, pipeline, mail, and other modes) on a monthly and annual basis. The value and weight of exports for air and water shipment are readily available. The export and import statistics are reported at the six-digit Harmonized System (HS) commodity detail starting from 2006.

Data are not available on the weight of U.S. exports by surface modes to Canada and Mexico from the TransBorder database or any other data source. As a result, the Bureau of Transportation Statistics (BTS) has been estimating the weights of U.S. exports to these countries based on the import weight-to-value ratios. However, the import weight-to-value ratios for a given commodity may drastically change from one year to another, resulting in inconsistent export weights estimates. The main purpose of this report is to produce a more consistent and reliable export estimates through a thorough analysis of the stability of the import weight-to-value ratios over time.

For estimating the U.S. export weights to Canada and Mexico, the import weight-to-value ratio approach is applied. First, import weight-to-value ratios at the different HS commodity levels of detail for each mode for U.S.-Canada and U.S.-Mexico are calculated. The value of exports multiplied by the import weight-to-value ratios provides the weight of exports. The import weight-to-value ratios are prepared at the country, mode, and HS commodity levels of detail. Second, using the decomposition statistical techniques for smoothing a time series, the method enables the removal of outliers or irregular components of most of the data at present, and to keep the same statistical method in the future. Finally, the annual weight-to-value ratios are applied to the export values to derive the weight of exports.

Method of transportation: The method of transportation is based on the method of transportation in use when the merchandise arrived at the U.S. Customs and Border Protection port of entry or departed a U.S. Customs and Border Protection port of exit. In some instances, shipments between the United States and countries abroad enter or depart the United States through Canada or Mexico. These are called transshipments. Such transshipments are recorded under the method of transportation by which they enter or depart a U.S. Customs and Border Protection port regardless of the transportation mode used between Canada or Mexico and the final country of origin or destination. For U.S. exports via Canada to other overseas countries, the mode reported would be the mode used to cross the U.S./Canadian border. If, for example, export shipments that are destined for the United Kingdom travel by truck through Buffalo/Niagara Falls, NY, and are then shipped by water from a Canadian port to the United Kingdom, the mode reported in U.S. international trade data would be truck.

Surface trade value data are not available from 1990 to 1994. While these data are available for 1995 and 1996, they include transshipment data that cannot be separated (making the sum of the parts greater than the official total published by Census Bureau). For the time period April 1993 through December 1996, transshipments were included in official U.S. trade data for land modes of transportation, and it is impossible to exclude these transshipments, measured in weight, at either a total land trade or individual modal level. Because of this inclusion of transshipment data for the land modes of transportation, a summation of the individual modal categories will exceed the U.S. total trade with Canada and Mexico for 1995 and 1996. Beginning in January 1997, transshipments are no longer included in the U.S. trade figures for land modes of transportation.

In contrast to transshipments, intransit shipments are goods declared by the shipper as moving through the United States from one foreign country to another and are not included in the official United States international merchandise trade statistics, and therefore are not included in this data for this table. In a North American context, intransit shipments would include, for example, a Canadian export to Mexico, which moves by truck through the United States. This type of activity, again, is not considered to be part of U.S. international trade, and is not reflected in official U.S. merchandise trade statistics, or in the data in this table.

Table 6-2c: U.S. Merchandise Trade With Canada and Mexico by Mode of Transportation (Thousands of metric tons)