The American Trucking Assns. (ATA) said today that its advance seasonally adjusted (SA) For-Hire Truck Tonnage Index decreased 1.4% in June, although May’s reduction was revised from 0.6% to just 0.1%. May and June marked the first back-to-back contractions since March and April 2009, ATA noted, pointing out that the latest reduction lowered the SA index from 110.1 (2000=100) in May to 108.5 in June.

ATA said the not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 115.9 in June, up 6.5% from the previous month.

Compared with June 2009, SA tonnage climbed 7.6%, which was just below May’s 7.7% increase and the seventh consecutive year-over-year gain. Year-to-date, tonnage is up 6.6% compared with the same period in 2009, ATA added.

According to ATA chief economist Bob Costello, the two sequential decreases reflect an economy that is slowing. Furthermore, growth in truck tonnage is likely to moderate in the months ahead as the economy decelerates and year-over-year comparisons become more difficult, he said.

Nevertheless, Costello believes that tonnage doesn’t have to grow very quickly at this point since industry capacity has declined so much. “Due to supply tightness in the market, any tonnage growth feels significantly better for fleets than one might expect,” he pointed out.