ARLINGTON, Va. — US truck tonnage contracted 0.9% in August after increasing 0.4% in July, according to reports from the American Trucking Associations. “The sequential drop in August, while not erasing the cumulative 1.5% gain in June and July, was significant,” the ATA said in a release. Compared with August 2011, the ATA’s seasonally-adjusted index was 3.2% higher. 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, was up 5.7% in August over July’s total.

“While there has been acceleration in housing during the last few months, truck tonnage is being weighed down by a flattening in manufacturing output and an unintentional increase in inventories throughout the supply chain,” said the ATA’s chief economist Bob Costello. “While choppy, tonnage has essentially been flat this year with August being the second lowest month of the year.” Costello also noted that the SA index in August was 0.3% below January and 1.4% less than the high in March.

“Expect tough year-over-year comparisons to continue through the rest of the year as tonnage grew nicely during the last five months of 2011,” he said, adding the economy isn’t expected to grow much in the second half of the year as manufacturing decelerates and excess inventories are worked off. As a result, tonnage is expected to increase less than 3.5% in 2012, the ATA said.