The American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index declined 1.1 percent in April 2008. March's tonnage reading, meanwhile, fell 1.7 percent instead of the previously reported 3.2 percent drop.

The seasonally adjusted tonnage index equaled 114.0 (2000 = 100) in April. The not seasonally adjusted index increased 1.5 percent to 116.9 from 115.1 in March.

The seasonally adjusted index was 2 percent higher compared with April 2007, marking the sixth consecutive year-over-year increase. The year-over-year reading in March was revised from a 0.1 percent contraction to a 1.5 percent gain.

ATA Chief Economist Bob Costello said the upward revision to March's tonnage was very positive, but warned that freight remains mixed. "Truck tonnage hasn't grown since January of this year on a month-to-month basis, suggesting the overall economy remains very soft," he said. "With that said, the fact that tonnage is showing sustained year-over-year growth is positive for the industry, although part of the strength is due to easy comparisons from 2007."

Costello added that rapidly rising fuel prices are by far a bigger problem for the motor carrier industry than freight volumes.

"Surging fuel prices are weighing heavily on consumers," he said. Since trucks haul virtually all consumer goods at some point in the supply chain, the industry is going to be significantly impacted both directly through higher diesel prices and indirectly as consumers pay more for gasoline and have less money to spend on truck-transported goods.

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. The report includes month-to-month and year-over-year results, relevant economic comparisons, and key financial indicators.