Measuring International Trade on U.S. Highways (2005) / Chapter Skim
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2 BTS Report: Summary of Findings
2 BTS Report: Summary of Findings
Pages 6-14
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From page 6... ...
evaluated the accuracy and reliability of the use of diesel fuel as a measure of international trade traffic by state; and (4) identified needed improvements in long-term data collection programs to help provide accurate and reliable measures of international traffic for use in formulas for highway apportionments (Bureau of Transportation Statistics, 2003)
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From page 7... ...
The errors and biases are due not only to typical sources, including sampling variance, nonresponse variance, and measurement error of various types, but also to various data deficiencies, even though the models mentioned above are used to overcome these deficiencies. The BTS study identified a number of sources of error for a variety of data sets used to estimate volumes and values for freight arriving here as imports or departing as exports, which we summarize below.
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From page 8... ...
There is no information about the degree of misresponse, which is typically unmeasured. However, 1The CFS data also support the ORNLs' highway network model and are included in public and private databases, such as the Federal Highway Administrations' Freight Analysis Framework and the Reebie Associates TRANSSEARCH database.
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From page 9... ...
Also, for those maritime shipments that are subsequently transported by truck, there are only limited data on the state of destination. This lack of direct information necessitates the use of models to estimate the quantities of tonmiles and value-miles for imports transported by highway at the state level.
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From page 10... ...
Foreign Waterborne Transportation Statistics, PIERS, and the Transborder Surface Freight Database provide important pieces of information, but each suffers from issues of data quality and compatibility. Furthermore, the BTS study found that many of the sources of data required to prepare and improve the estimates of international trade traffic by highway by state are collected under pledges of confidentiality and are protected from other use by legal mandate.
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From page 11... ...
Access to customs data would alleviate many, but not remove all, of the five above deficiencies in current data. COUNTY-LEVEL DATA Since knowing only the state of destination provides limited information as to the specific highways used, it is important to "carry down" information on import freight movements from the state level to the county level.
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From page 12... ...
The model is a geographically based network of major roadways, currently representing 420,000 miles, which simulates shipment routes by roads from two points. The benefit of having this highway model embedded in the ORNL intermodal network model allows one to model, based on transportation costs and travel time, whether freight that is moving from one point to another is likely to be transported using trucks, trains, waterways, or by air.
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From page 13... ...
Therefore, there is no direct way to use only that portion of diesel fuel data to model international trade traffic by state. BTS carried out a modification of the required analysis, using diesel fuel data at the state level as the independent variable in a simple linear regression to model the dependent variable ton-miles of highway traffic-not ton-miles of international highway traffic.
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From page 14... ...
In particular, the regression model failed to account for changes over time in the fuels used to drive trucks and the changes in demand for diesel fuel from other uses. As requested in TEA-21, BTS was asked not only to provide estimates of ton-miles and value-miles of international highway trade traffic, but also to investigate the reliability of these estimates.
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