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Improvements in BTS Estimation of Ton-Miles

Scott M. Dennis

Abstract

Ton-miles (one ton of freight shipped one mile) is the primary physical measure of freight transportation output. This paper describes improved measurements of ton-miles for air, truck, rail, water, and pipeline modes. Each modal measure contains a discussion of the data sources used and methodology employed, presents a comparison with other well-known measures for reference purposes, and discusses the limitations of the data used. The resulting measures provide more comprehensive and more reliable coverage of transportation activity than do existing measures, especially with respect to trucking and natural gas pipelines.

KEYWORDS: freight traffic measurement, ton-miles

The Bureau of Transportation Statistics (BTS) is considering improvements to some of its basic measures of transportation activity. This report describes proposed ton-mile measures for air, truck, rail, water, and pipeline modes. Each modal measure contains a discussion of the data sources used and methodology employed, presents a comparison with other well-known measures for reference purposes, and discusses the limitations of the data used. This report should be viewed as part of a continuing series of steps forward. Additional work will allow BTS to further improve its basic measures of transportation activity.

Concept

Ton-miles is the primary physical measure of freight transportation output. A ton-mile is defined as one ton of freight shipped one mile, and therefore reflects both the volume shipped (tons) and the distance shipped (miles). Ton-miles provides the best single measure of the overall demand for freight transportation services, which in turn reflects the overall level of industrial activity in the economy. There does not presently appear to be any complete, reliable estimate of this basic transportation measure. In addition, a ton-mile measure is necessary in order to construct other measures of transportation system performance, such as energy efficiency and accident, injury, and fatality rates.

Data Sources

Measures of domestic ton-miles (traffic within and between the 50 States, District of Columbia, Puerto Rico, and the United States Virgin Islands) were developed in order to maintain compatibility with other DOT Strategic Plan data. Ton-mile measures were estimated on an annual basis in order to illustrate long-term trends. In order to provide comprehensive coverage, the ton-mile measures are a combination of reported data from established sources, estimates from surveys, and calculations based on certain assumptions. Table 1 provides a brief comparison of the scope of the improved BTS ton-mile measures with two other well-known measures: estimates currently published by BTS in National Transportation Statistics (NTS) [10], and estimates published by the Eno Transportation Foundation (Eno) [2]. Figure 1 presents the improved BTS ton-mile measures for all modes, as well as the other well-known ton-mile measures.

Table 1: Comparison of Annual Data Coverage

Air

Air freight ton-mile measures are presented in Figure 2. Annual air freight data were taken from Air Carrier Traffic Statistics Monthly [12], which presents the results of the T-100 reporting system, supplemented with special tabulations of data on domestic all-cargo operators from the Federal Aviation Administration (FAA).

The T-100 data represent the population of all domestic freight traffic for Section 401 carriers, which operate planes with a passenger seating capacity of more than 60 seats, or a maximum payload capacity of more than 18,000 pounds. These data include the vast majority of all domestic air freight traffic. As a result of a BTS rulemaking, data for smaller carriers will be included in this source starting with the fourth quarter of 2003. The inclusion of smaller carriers is not expected to substantially affect the results. Domestic all-cargo operators (Section 418 carriers) have been gradually integrated into Air Carrier Traffic Statistics Monthly. The FAA data captured those carriers who had not yet reported in Air Carrier Traffic Statistics Monthly, thus allowing representation of the full population of domestic all-cargo operators.

The proposed measure of air-freight ton-miles is essentially the same as the Eno measure. Neither measure includes private carriage of air freight or air freight forwarders who do not use T-100 reporting carriers. These exceptions are likely to account for well under five percent of all air freight traffic. The substantial difference between the two data series in 2001 apparently is due to Eno’s use of preliminary data.

Truck

Oak Ridge National Laboratory produced estimates of truck ton-miles based on the 1993 and 1997 Commodity Flow Survey (CFS) [13] and supplemented with data on farm-based shipments and imports arriving by truck from Canada and Mexico. The 1997 estimate of truck ton-miles is reported in Transportation Statistics Annual Report [11]. The 1993 and 1997 estimates were then updated and backdated using intercity and intracity vehicle miles traveled (VMT) for single unit and combination trucks as reported in Highway Statistics [14]. The resulting estimates are presented in Figure 3. The trend in both series is the same because the same VMT data were used to update both series. After making these adjustments for different time periods and population coverage, the difference between the 1993 and 1997 estimates is less than two percent.

The CFS captures export movements, as well as movements of imports once they have reached their first domestic destination, such as a warehouse. In order to provide a more complete estimate of truck traffic, the data in Figure 3 were further adjusted to reflect truck ton-miles from maritime movements prior to reaching their first domestic destination. The number of loaded twenty foot equivalent unit containers (TEU’s) shipped through U.S. ports is reported in Maritime Trade and Transportation [9]. These figures were then divided by 2.4 to convert to an equivalent number of 48 foot trucks. Estimates of the percentage of import traffic, truck share of import traffic, miles to first domestic destination, and tons per truck for east, gulf, and west coast ports were obtained through interviews with port personnel in New York, Houston, and Los Angeles respectively. The resulting estimates added between 7 and 12 billion truck ton-miles each year. This represents approximately one percent of all truck ton-miles currently estimated.

Trucking ton-mile estimates are presented in Figure 4. The improved BTS estimates are based on the Oak Ridge National Laboratory supplement to the 1997 study, which is the more recent of the two studies. The improved BTS measure is about 10 percent greater than the NTS and Eno measures, each of which reflect only intercity truck traffic. The improved BTS measure therefore provides a more comprehensive measure of truck traffic.

The CFS data used to construct the improved trucking ton-miles measure exclude shipments by households, retail, service, and government establishments (including U.S. Mail); and certain non-commercial freight shipments, such as municipal solid waste. The NTS and Eno measures do not include intracity traffic. It therefore appears that a significant percentage of truck VMT and a somewhat smaller percentage of truck ton-miles are not included in any of these measures. Clearly more work is needed in this area.

Railroad

Annual railroad ton-miles were developed from the Carload Waybill Sample [15]. The population estimate in this source is based on a 500,000 record sample of all traffic terminating on all railroads in the United States. It is our understanding that the sample implicitly includes traffic originating on U.S. railroads and terminating on Mexican railroads, since almost all such traffic is rebilled to U.S. border crossings.

Population data on the tonnage of railroad shipments originating in the United States and terminating in Canada were obtained from Transportation in Canada [3]. The average length of haul for U.S. railroad shipments was applied to this tonnage to obtain an estimate of U.S. railroad ton-miles for shipments terminating in Canada. While much of this traffic originates in states bordering Canada, the amount of such traffic originating in more distant states such as California, Texas, and Georgia makes this a reasonable assumption.

Railroad ton-mile measures are presented in Figure 5. Over the last four years, the improved BTS estimates are about five percent greater than the NTS estimates, which include only Class I railroads; about one percent greater than the Waybill estimates, which do not include Canadian terminations; and almost identical to the Eno estimates, which include both non-Class I railroads and Canadian terminations. However, Eno’s ton-mile estimates for non-Class I railroads are based on financial survey data. The improved BTS estimates are based on actual ton-mile data and should be considered more reliable.

Railroad ton-mile data may not include shipments which originate in Mexico and terminate in Canada. Based on data from Transport Canada, it appears that these shipments account for less than one tenth of one percent of all U.S. railroad traffic.

Water

Domestic waterborne ton-mile measures are presented in Figure 6. Annual water transportation ton-miles were taken from Waterborne Commerce of the United States [4]. Data in this source are developed from lock data and individual trip reports which must be filed with the U.S. Coast Guard. This source therefore represents the entire population of all domestic water traffic, including inland waterways, coastwise, Great Lakes, and intraport traffic, along with traffic to and from Alaska, Hawaii, and Puerto Rico. The substantial difference between the NTS and Eno estimates reflects NTS’s inclusion of coastwise (domestic ocean) traffic. The NTS measure, which is proposed for use here, is more comprehensive than Eno’s estimate.

Pipeline

Pipeline ton-miles are presented in Figure 7. Annual oil and oil products pipeline ton-miles were obtained from Shifts in Petroleum Transportation [1]. These data represent the entire population of crude petroleum and petroleum products carried in domestic transportation by both Federally regulated and non-Federally regulated pipelines. Both NTS and Eno use this measure, which is also proposed for use here.

Natural gas pipeline ton-miles are also presented in Figure 7. The estimate of natural gas pipeline ton-miles is based on natural gas deliveries reported in Annual Energy Review [5]. The gas deliveries, measured in cubic feet, were converted first to metric tons and then to tons using a standard conversion factor of 48,700 cubic feet per metric ton reported in International Energy Annual [6]. There are no available data on length of haul for natural gas shipments, since natural gas is drawn from a common pipeline, rather than shipped to a specific consignee. Origination and termination data from the U.S. Department of Energy, Energy Information Administration [7, 8] indicate that natural gas has a distribution pattern similar to oil and oil products. Therefore, the length of haul for oil and oil products was applied to the tonnage of natural gas to estimate natural gas ton-miles in transmission lines. Natural gas ton-miles in distribution lines (i.e., local utilities) were estimated using five percent of transmission length of haul, which is approximately half the diameter of a major metropolitan area. Natural gas ton-miles in gathering lines (i.e., from well to processing plant) were estimated using the same length of haul as in distribution lines. The ton-miles for gathering, transmission, and distribution lines were then summed to provide an estimate of total natural gas ton-miles. Natural gas ton-miles, which have not to our knowledge been previously estimated, represent nearly as much traffic as carried on the inland waterway system. These new estimates fill a substantial gap in the existing ton-mile data.

The natural gas pipeline data do not include gas used to repressurize gas fields or power the pipeline itself, since these uses do not represent gas carried in revenue transportation. The pipeline data also exclude coal slurry, ammonia, and other types of pipelines. There are only a few such pipelines, which tend to have either short haul or low volume, and appear to account for well under one percent of all pipeline ton-miles.

References

[1] Association of Oil Pipelines. Shifts in Petroleum Transportation. Washington: Association of Oil Pipelines, 2002, Table 1.

[2] Eno Transportation Foundation. Transportation in America. Washington: Eno Transportation Foundation, 2002, p. 42.

[3] Transport Canada. Transportation in Canada, Addendum. Ottawa, Canada: Transport Canada, 2002, Table A6-10.

[4] U.S. Army Corps of Engineers, Waterborne Commerce of the United States, Part V, Section 1, Table 1-4, Total Waterborne Commerce.

[5] U.S. Department of Energy, Energy Information Administration. Annual Energy Review. Washington: Energy Information Administration, 2001, Table 6.5.

[6] _____. International Energy Annual. Washington: Energy Information Administration, 2001, Table C-1.

[7] _____. Natural Gas Annual 2002. Washington: Energy Information Administration, 2004, Table 12.

[8] _____. Petroleum Supply Annual 2002, Volume 1. Washington: Energy Information Administration, 2003, Table 33.

[9] U.S. Department of Transportation, Bureau of Transportation Statistics. Maritime Trade and Transportation. Washington: Bureau of Transportation Statistics, 2002, Table 1-20.

[10] _____. National Transportation Statistics. Washington: Bureau of Transportation Statistics, 2003, Table 1-44.

[11] _____. Transportation Statistics Annual Report. Washington: Bureau of Transportation Statistics, 2000, p. 124.

[12] _____, Office of Airline Information. Air Carrier Traffic Statistics Monthly. p. 2, line 3, Freight, Express, and Mail Revenue Ton-Miles.

[13] U.S. Department of Transportation, Bureau of Transportation Statistics, and U.S. Department of Commerce, Economics and Statistics Administration, Census Bureau . Commodity Flow Survey. Washington: Bureau of Transportation Statistics, 1992, 1997.

[14] U.S. Department of Transportation, Federal Highway Administration. Highway Statistics. Washington: Federal Highway Administration, 2002, Table VM-1.

[15] U.S. Department of Transportation, Surface Transportation Board, Carload Waybill Sample.