Truck Tonnage 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

The Transportation Services Index (TSI) uses the Monthly Truck Tonnage Report (MTTR), issued by the American Trucking Associations (ATA). The ATA report contains an index that is a relative measure of the total tonnage transported by the motor carrier industry for the given month. There is a one-month lag between the end of the data month and the time when ATA reports the index number for the data month. ATA revises the index number in the following month. The data have been collected since the 1973.

Methodology

For an explanation of the methodology used in the Monthly Truck Tonnage Report (MTTR), please see the MTTR sample file, available at http://www.truckline.com/ (link is external).

ATA weights the index to reflect the composition of the trucking industry.

Collection

ATA samples a small proportion of the trucking industry. ATA promises confidentiality to the companies providing the data. As a result, ATA does not publicize which companies respond or how often, what type of freight that they carry, or what proportion of the total truck tonnage they represent. The data series itself is an index calculated from the raw data ATA collects.

Data Series Volatility

The Truck Tonnage displays significant volatility as measured by the number of times it changes direction over a defined period of time. For example, the unadjusted Truck Tonnage index changed direction in 231 of the 367 months between March 1973 and September 2003. In comparison, the BLS Consumer Price Index (CPI-U) changed direction only 36 times over that same period.

Data Quality Questions

Coverage/Completeness

Is this data source a frame or sample?
ATA produces the index from a survey of the total tons of intercity freight transported by motor carriers. This includes both large and small truckload carriers, along with less-than-truckload carriers.

Does the sample cover the entire frame? Or is there some group that is missing or underrepresented in the sample? For the excluded group, what percentage of the total do they make up?
The data cover for-hire trucking only and respondents are only ATA members. It is unclear the proportion ATA members comprise of the trucking industry, because ATA does not publicize which companies respond to their survey.

Timeliness

Are the data available monthly?
Yes.
How soon are the data available after the month is over?
The data are available approximately five weeks after the end of a month.
Are the data easy to access and use?
Yes.
Are the microdata available for use?
No. All collected data are confidential and only available in summary form.

Accuracy

Are there duplicate records?
There may be duplicate data in the tonnage. ATA considers this to be normal for tonnage data and of no great impact.
Are there outliers in the data?
Rarely.
Are data missing for individual records? If so, how are they identified?
Not applicable.
How accurate are the key data fields?
BTS is unable to determine.
Are variances available for this data source? If so, what method was used to calculate variances?
Standard deviation is 4.3% according to ATA.

Comparability

Are the data comparable over time within the data source? If not, can data be made to be comparable (i.e., combining two data series)?
Yes, the data are comparable.

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