Compared with June 2012, the SA index surged a robust 5.9 percent although it was below May's 6.5-percent year-over-year gain, according to the ATA. Year-to-date, compared with the same period in 2012, the tonnage index is up 4.7 percent.
The not-seasonally-adjusted index, representing the change in tonnage actually hauled by fleets before any seasonal adjustment, equaled 125.9 in June, which was 5 percent below the previous month's index of 132.4, the group said.
"The fact that tonnage didn't fall back after the 2.1-percent surge in May is quite remarkable," ATA Chief Economist Bob Costello said. "While housing starts were down in June, tonnage was buoyed by other areas like auto production, which was very strong in June and durable-goods output, which increased 0.5 percent during the month according to the Federal Reserve."
"Robust auto sales also helped push retail sales higher, helping tonnage in June." he added. "The trend this year is heavy freight, like autos and energy production, is growing faster than lighter freight, which is pushing truck tonnage up."
Regarding the impact of trucking company failures on the index, the ATA noted that each month it asks its membership the amount of tonnage each carrier hauled, including all types of freight, with the indexes calculated based on those responses. The sample includes an array of trucking companies, ranging from small fleets to multi-billion dollar carriers.
When a company in the sample fails, the association said it includes that firm's final month of operation and zeroes it out for the following month, with the assumption that the remaining carriers pick up that freight.
"As a result, it is close to a net wash and does not end up in a false increase. Nevertheless, some carriers are picking up freight from failures and it may have boosted the index," the ATA said, adding that due to its correction, the affect should be limited.
"Trucking serves as a barometer of the U.S. economy, representing 68.5 percent of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods," the association said. "Trucks hauled 9.4 billion tons of freight in 2012. Motor carriers collected $642.1 billion, or 80.7 percent of total revenue earned by all transport modes."
The ATA, which has been calculating its tonnage index based on surveys from its membership since the 1970s, said this index is a preliminary figure and subject to change in the final report issued around the tenth day of the month. The report includes month-to-month and year-over-year results, relevant economic comparisons, and key financial indicators.
The ATA is the nation's largest national trade association for the trucking industry, comprising a federation of 50 affiliated state trucking associations and industry-related conferences and councils.