Truck Tonnage

Source: Truck Tonnage Index, calculated by the American Trucking Association (private/proprietary).

General

The TSI uses the “Monthly Truck Tonnage Report” (MTTR), issued by the American Trucking Associations (ATA). The ATA report contains an index (2000 = 100) 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 the index number for the data month is reported; the index number is revised over 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/ .

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

Data Quality Questions

Collection

ATA indicated that its promises of confidentiality to the companies providing the data prevent them from providing any details that would permit an independent assessment of this data. No information is available regarding which companies respond or how often, what type of freight that they carry, or what proportion of the total truck tonnage they represent. In any case, voluntary response surveys can never be treated as probability based statistical samples.

The ATA “sample” is based on a relatively small proportion of the trucking industry. The data series itself is an index for which the raw data are unavailable making it difficult to corroborate against other data.

Data Series Volatility

As the major component of an index that is expected to perform as an economic indicator, the Truck Tonnage index is unusually volatile for a series that might be expected to maintain a generally upward direction. Comparing consecutive months of the unadjusted Truck Tonnage index shows that it changed direction in 231 of the 367 months between March 1973 and September 2003 . The BLS Consumer Price Index (CPI-U) changed direction only 36 times over that same period.

Coverage/Completeness

• Is this data source a frame or sample?
  This tonnage data are produced from a voluntary response survey of the ATA membership. The member agrees to provide data in exchange for the report. Therefore, the data source is a sample.  ATA made an effort to establish weights for the data so that the sample is representative of the industry.
• 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?
  It is impossible for BTS to determine whether there is under-representation in the truck tonnage index from ATA due to the confidentiality of the data. The data cover for-hire trucking only and respondents are only ATA members.

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. Reported outliers are researched. ATA may do adjustment for certain outliers.
• 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.

Other Questions

• Is sufficient documentation available for the data source?
• Data dictionary:
  Information is not available to BTS.
• Detailed description of the 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/economics.
  ATA weights the index to reflect the composition of the trucking industry.
• Estimation methods:
  Information is not available to BTS.
• Are other sources available for the same data?
  Other sources of data are not as timely and are not monthly. Monthly and timely data are requirements for the TSI.
• Who is the contact for the data source?
  American Trucking Association, econdept@trucking.org