The American Trucking Associations' advance seasonally adjusted (SA) For-Hire Truck Tonnage Index increased 2.8% in June after decreasing a revised 2.0% in May 2011. May's drop was slightly less than the 2.3% ATA reported on June 27, 2011. The latest gain put the SA index at 115.8 (2000=100) in June, up from the May level of 112.6 and the highest since January 2011.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 122.3 in June, which was 5.3% above the previous month.

Compared with June 2010, SA tonnage jumped 6.8%, the largest year-over-year gain since January 2011. In May, the tonnage index was 3% above a year earlier.

'Motor carriers told us that freight was strong in June and that played out in the data as well,' ATA Chief Economist Bob Costello said.' Tonnage recovered all of the losses in April and May when the index contracted a total of 2.6%.

'After growing 5.5% in the first half of the year from the same period last year, the strength of truck tonnage in the second half will depend greatly on what manufacturing output does,' Costello noted. 'If manufacturing continues to grow stronger than GDP, I fully expect truck freight to do the same.'

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.