The American Trucking Associations' June tonnage index had its largest month-to-month gain so far this year, thanks to a larger-than-estimated loss the previous month. Tonnage is still up year over year.

The advanced seasonally adjusted For-Hire Truck Tonnage Index rose 1.2% in June after falling 1.0% in May. May's loss was larger than the 0.7% drop ATA reported on June 19.

June's increase was the largest month-to-month gain in 2012. However, the index contracted a total of 2.1% in April and May. The latest gain increased the SA index to 119.0 (2000=100), up from May's level of 117.5.

Compared with June 2011, the SA index was 3.2% higher, the smallest year-over-year increase since March 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 123.0 in June, which was 0.9% below the previous month.

For the second quarter, the SA index was off 0.8% from the previous quarter, which was the first decrease in a year. Compared with the second quarter in 2011, the index was up 3.5%.

"June's increase was a pleasant surprise, but the lower year-over-year gain fits with an economy that has slowed," ATA Chief Economist Bob Costello said. "Manufacturing output was strong in June, which helped tonnage levels."

Costello said he's still concerned about businesses sitting on cash instead of hiring more workers or spending it on capital, both of which would give the economy and tonnage a shot in the arm, as they are worried about Europe and the U.S. fiscal cliff at the end of the year. Costello lowered his tonnage outlook for 2012 to the 3% to 3.5% range due to recent economic weakness.

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.