The American Trucking Associations' advance seasonally adjusted (SA) For-Hire Truck Tonnage Index decreased 0.6 percent in May, which was the first month-to-month drop since February of this year. This followed an upwardly revised 1 percent increase in April. 'The latest reduction put the SA index at 109.6 (2000=100).

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 108.3 in May, down 2.8 percent from the previous month.

Compared with May 2009, SA tonnage increased 7.2 percent, which was the sixth consecutive year-over-year gain. In April, the year-over-year increase was 9.5 percent. Year-to-date, tonnage is up 6.2 percent compared with the same period in 2009.

ATA Chief Economist Bob Costello said that truck freight tonnage is going to have ups and downs, but the trend continues in the right direction. 'Despite the month-to-month drop in May, the trend line is still solid.' There is no way that freight can increase every month, and we should expect periodic decreases.' This doesn't take away from the fact that freight volumes are quite good, especially considering the reduction in truck supply over the last couple of years.''

Note on the impact of trucking company failures on the index: Each month, ATA asks its membership the amount of tonnage each carrier hauled, including all types of freight.' The indexes are calculated based on those responses.' The sample includes an array of trucking companies, ranging from small fleets to multi-billion dollar carriers. When a company in the sample fails, we include its final month of operation and zero it out for the following month, with the assumption that the remaining carriers pick up that freight.' As a result, it is close to a net wash and does not end up in a false increase.' Nevertheless, some carriers are picking up freight from failures, and it may have boosted the index. Due to our correction mentioned above, however, it should be limited.

Trucking serves as a barometer of the U.S. economy, representing 68 percent of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods.

Trucks hauled 8.8 billion tons of freight in 2009. 'Motor carriers collected $544.4 billion, or 81.9 percent 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.