The American Trucking Associations' advance seasonally adjusted (SA) For-Hire Truck Tonnage Index decreased 2.3% in May after decreasing a revised 0.6% in April 2011. April's drop was slightly less than the 0.7% ATA reported on May 25, 2011.' The latest drop put the SA index at 112.3 (2000=100) in May, down from the April level of 114.9.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 115.9 in May, which was 2% above the previous month.

Compared with May 2010, SA tonnage climbed 2.7%, although this was the smallest year-over-year gain since February 2010.' In April, the tonnage index was 4.8% above a year earlier.

'Truck tonnage over the last four months shows that the economy definitely hit a soft patch this spring,' ATA Chief Economist Bob Costello said. 'With our index falling in three of the last four months totaling 3.7%, it is clear why there is some renewed anxiety over the economic recovery.'

However, Costello added that he is cautiously optimistic that freight volumes will improve in the second half of the year along with economic activity.

'With oil prices falling and some of the Japan-related auto supply problems ending, I believe this was a soft patch and not a slide back into recession, and we should see better, but not great, economic activity in the months ahead,' he said.

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 67.2% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 9 billion tons of freight in 2010. 'Motor carriers collected $563.4 billion, or 81.2% 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.