The American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index increased on a month-to-month basis for the first time since January of this year, edging 0.5% higher in May. April's tonnage reading fell a revised 0.6% instead of the previously reported 1.1% drop.

The seasonally adjusted tonnage index equaled 114.8 (2000 = 100) in May. The not seasonally adjusted index increased 1.1% to 118.3 from 117.1 in April.

The seasonally adjusted index was 3.3% higher compared with May 2007, marking the seventh consecutive year-over-year increase. In April, the year-over-year gain was 2.2%.

ATA Chief Economist Bob Costello said that May's tonnage reading represents a positive step forward, but noted that freight volumes remain mixed across the industry amid continuously rising fuel prices and a weak economy.

"The fact that tonnage increased on a month-to-month basis for the first time in four months, as well as achieving its largest year-over-year gain since February of this year, is quite positive," Costello said. "However, year-over-year comparisons continue to reflect the weakness of 2007 rather than robust growth in 2008."

High diesel fuel prices continue to place a significant burden on motor carriers, he said. "Rising fuel prices are a double-edged sword for the industry," Costello said. "Since trucks haul virtually all consumer goods at some point in the supply chain, the industry is significantly impacted both directly through high diesel prices and indirectly as consumers have less money to spend on truck-transported goods."

Trucking serves as a barometer of the U.S. economy because it represents nearly 70% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods.

Trucks hauled 10.7 billion tons of freight in 2006. Motor carriers collected $645.6 billion, or 83.8% of total revenue earned by all transport modes.

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.

The American Trucking Associations is the largest national trade association for the trucking industry. Through a federation of other trucking groups, industry-related conferences, and its 50 affiliated state trucking associations, ATA represents more than 37,000 members covering every type of motor carrier in the United States.