Rail Freight Carloads and Intermodal Traffic Used in the Transportation Services Index

Friday, November 22, 2024

Return to all data sources used in the Bureau of Transportation Statistics’ Transportation Services Index.

General

Rail freight in the Transportation Services Index (TSI) are from the Association of American Railroads publication, Weekly Railroad Traffic (WRT). The WRT shows weekly carload and intermodal traffic originating in the U.S. and Canada, neither of which are not a direct measure of ton-miles. BTS includes the U.S. traffic data in the TSI. U.S. traffic reflects the U.S. and Canadian operations of U.S. railroads. This applies to both carload and intermodal traffic.

Methodology

BTS converts WRT weekly data to monthly numbers by calculating an average daily number from the weekly data and then multiplying that number by the number of days of that week that occur in a particular month. There are two separate series: (1) carload traffic and (2) number of intermodal units. For both series, the monthly numbers calculated by BTS are different from the monthly numbers published by AAR. AAR assigns each week to a particular month. AAR assigns weeks completely within a particular month to that month and assigns weeks that bridge two months to the month in which more of their days fall. AAR then sums the weekly values assigned to the month. The assignation results in some months having 4 weeks and some having 5 weeks. To create a series of comparable monthly values, AAR averages weekly values for each month.

The two series present two slightly different aspects of monthly freight activity due to different commodity mixes, traffic, etc.. Carload traffic consists mostly of bulk commodities, such as coal (46% of rail tonnage in 2001), agricultural products, and nonmetallic minerals and products, while rail intermodal transports a huge range of goods from bicycles to automotive parts, lawnmowers to glassware, greeting cards to bottled water, and toys to computers. Globalization geographically expanded manufacturers’ supply chains , and rail intermodal plays a critical role in making supply chains more efficient for retailers and other firms and industries.

Data Quality Questions

Coverage/Completeness

Is this data source a frame or sample?
WRT is a sample of all U.S railroads. The accounting departments for the reporting railroads report all revenue movements during the week to the Association of American Railroads (AAR) for inclusion in the WRT.
Does the sample cover the entire frame? Or is some group missing or underrepresented in the sample? For the excluded group, what percentage of the total do they make up?
Not all U.S. railroads report to AAR. All U.S. Class I railroads submit data but of the nearly 500 non-Class I railroads in the U.S., about 10 of them submit data to AAR.

Reporting to the WRT is voluntary. Using the Surface Transportation Boards Rail Waybill Sample to estimate how much of total U.S. traffic is covered in the WRT, AAR concluded that the WRT covers 87 percent of carloads and 96 percent of intermodal units. However, this does not include the U.S. operations of Canadian owned railroads. Canadian parent companies, Canadian National (CN) and Canadian Pacific (CP), report traffic for the former Illinois Central, Grand Trunk Western, and Soo line (among others). All of U.S. the traffic on these lines appears in the Canadian totals of the WRT. CN and CP do not separate out the carloads originating in the U.S. from the rest of their traffic in the WRT. Adding U.S.-originated CN and CP traffic to the other U.S. traffic, the WRT covers 96 percent of carloads and 100 percent of intermodal originated in the U.S.

Timeliness

Are the data available monthly?
Weekly data are converted to monthly numbers by BTS. See the Methodology section above for details.
How soon are the data available after the month is over?
There is a 1-week lag time after the end of the period for the weekly data.
Are the data easy to access and use?
BTS receives a file from AAR weekly. AAR provides the latest weekly numbers on their website.
Are the microdata available for use?
The latest weekly numbers are available on the AAR website. Historical data can be purchased.

Accuracy

Are there duplicate records?
There do not appear to be duplicate records for weekly carload and intermodal traffic.
Are there outliers in the data?
No.
Are data missing for individual records? If so, how are they identified?
AAR says there are no missing data in the WRT. All reporting carriers submit data every week.
How accurate are the key data fields?
For the time they are reported, the data are accurate. Each car origination is counted once. Some railroads submit minor revisions to weekly data in the same week of the following year. Other railroads submit revisions to their data upon discovering an error, which happens infrequently. Revisions to the traffic data may be submitted by reporting railroads through the end of the following calendar year. When a railroad is unable to submit its traffic figures for the current week, AAR repeats the value from the previous week. AAR replaces these values with carrier-reported numbers as soon as possible.
Are variances available for this data source? If so, what method was used to calculate variances?
No.

Comparability

Are the data comparable over time within the data source? If not, can data be made to be comparable (e.g., combining two data series)?
Yes, data are comparable. The WRT compares the current week to the same week ending 52 weeks earlier.

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