The American Trucking Associations’ advanced seasonally adjusted For-Hire Truck Tonnage Index increased 1.2 percent in June after falling 1.0 percent in May. June’s increase was the largest month-to-month gain in 2012, but the index contracted a total of 2.1 percent in April and May.

The latest gain increased the adjusted index to 119.0, up from May’s level of 117.5. Compared with June 2011, the adjusted index was 3.2 percent higher, the smallest year-over-year increase since March. Year-to-date, compared with the same period last year, tonnage was up 3.7 percent.

The nonseasonally 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 percent below the previous month.

For the second quarter, the adjusted index was off 0.8 percent 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 percent.

“June’s increase was a pleasant surprise, but the lower year-over-year gain fits with an economy that has slowed,” said Bob Costello, ATA chief economist. “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. He lowered his tonnage outlook for 2012 to the 3 percent to 3.5 percent range due to recent economic weakness.

ATA calculates the tonnage index based on surveys from its membership. The report includes month-to-month and year-over-year results, relevant economic comparisons, and key financial indicators. The baseline year is 2000.