ARLINGTON, VA. — The American Trucking Associations’ (ATA) advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index increased 0.4 percent in September after falling 0.9 percent in August.

September’s index was the same as January 2012, ATA said, explaining that the index has been on a flat trend-line over the past 9 months.

Compared with September 2011, the SA index was 2.4 percent higher, the smallest year-over-year increase since December 2009. Year-to-date, compared with the same period last year, tonnage was up 3.6 percent.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, was 9 percent below the previous month.

During the third quarter, SA tonnage increased 0.4 percent from the previous quarter and 3.4 percent from the same quarter in 2011.

“The year-over-year deceleration in tonnage continued during September, although I was encouraged that the seasonally adjusted index edged higher from August,” ATA Chief Economist Bob Costello said.

Costello noted again this month that the acceleration in housing starts, which is helping truck tonnage, is being countered by a flattening in manufacturing output and elevated inventories throughout the supply chain.

“Expect year-over-year comparisons to continue shrinking through the rest of the year as tonnage grew nicely during the last three months of 2011,” he said. As a result, tonnage is expected to increase less than 3.5 percent in 2012.