The American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index was unchanged in July after increasing 1.1% in June.

June's gain was slightly smaller than the preliminary estimate of 1.2% increase ATA reported on July 25. In July, the SA index stayed at 118.8 (2000=100).

Compared with July 2011, the SA index was 4.1% higher, the largest year-over-year gain since February 2012. Year-to-date, compared with the same period last year, tonnage was up 3.7%.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 119.4 in July, which was 2.8% below the previous month.

"July's reading reflects an economy that has lost some steam, but hasn't stalled," ATA Chief Economist Bob Costello said. "Certainly there has been some better economic news recently, but I continue to believe we will see some deceleration in tonnage during the second half of the year, if for nothing else but very tough comparisons on a robust August through December period in 2011."

Costello said he believes the slowdown in new factory orders will constrain manufacturing output, which will impact truck freight volumes. He's also concerned about the recent jump in the total business (manufacturing, wholesale, and retail) inventory-to-sales ratio.

"Unintended gains in inventories will hit trucking negatively as the supply chain works off stocks," he says.

Costello kept his tonnage outlook for 2012 to the 3% to 3.5% range as reported last month.

ATA calculates the tonnage index based on surveys from its membership and has been doing so since the 1970s. This is a preliminary figure and subject to change in the final report issued around the 10th day of the month.