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July 25 (Reuters) - The index that tracks tonnage hauled by American trucks rose 1.2 percent in June, after falling a revised 1 percent in May, due to the increase in industrial production in that month, the American Trucking Associations (ATA) said on Wednesday.
The index was also 3.2 percent higher than a year earlier, logging the smallest year-over-year increase since March, the associations said.
"Manufacturing was doing better in June and that is a big part of the increase in the index," said ATA Chief Economist Bob Costello.
"But the rise didn't wipe out the declines in April and May," that were caused by the sluggish economy, he added.
Costello revised ATA's 2012 trucking index outlook and expects the index to rise about 3 to 3.5 percent this year, compared to a high of 3.9 percent in earlier estimates.
"One month's data doesn't equal a trend. We still believe the economy has slowed," he said.
The index rose by 5.8 percent in 2011.
Analysts track the trade group's tonnage index to gauge the health of U.S. manufacturing and, particularly, the strength of diesel demand.
About 67 percent of all tonnage in the United States is hauled on trucks, according to the ATA, which calculates the tonnage index based on surveys from its members.
The June non-seasonally adjusted index was 0.9 percent lower than May levels.
Reporting by Selam Gebrekidan; Editing by Gerald E. McCormick and Tim Dobbyn