ARLINGTON, Va., April 23, 2013 /PRNewswire-USNewswire/ -- The American Trucking Associations' advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index gained 0.9% in March after decreasing 0.7% in February. (The 0.7% loss in February was revised down from a 0.6% increase ATA reported on March 19, 2013.) Tonnage has now increased in four of the last five months. Specifically, since November 2012, the index is up 7.6%. In March, the SA index equaled 123.5 (2000=100) versus 122.3 in February. The highest level on record was December 2011 at 124.3. Compared with March 2012, the SA index was up a solid 3.8%, beating February's 3.1% year-over-year gain. Year-to-date, compared with the same period in 2012, the tonnage index is up 3.9%. (Logo: http://photos.prnewswire.com/prnh/20100129/ATALOGO ) The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 125.2 in March, which was 11.5% above the previous month (112.3). "Fitting with the expectation for solid gross domestic product growth in the first quarter, tonnage was strong in March and the quarter overall," ATA Chief Economist Bob Costello said. "At 3.9% year-over-year growth, the first quarter increase was the best since the final quarter 2011. "Expect freight tonnage will slow in the months ahead as the federal government sequester continues and households finish spending their tax returns," he said. "The good news for tonnage is housing starts are growing and energy production is good – both of which generates heavy freight. However, these two sectors alone won't be enough to keep the overall index growing at a 3.9% clip in the second quarter." 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% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 9.2 billion tons of freight in 2011. Motor carriers collected $603.9 billion, or 80.9% 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.