The American Trucking Associations' advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index jumped 6.8% in December after rising 0.3% in November 2011. The latest gain put the SA index at 124.5 in December, up from the November level of 116.6.

For all of 2011, tonnage rose 5.9% over the previous year – the largest annual increase since 1998. Tonnage for the last month of the year was 10.5% higher than December 2010, the largest year-over-year gain since July 1998. November tonnage was up 6.1% over the same month last year.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 116.4 in December, which was 0.8% above the previous month.

"While I'm not surprised that tonnage increased in December, I am surprised at the magnitude of the gain," ATA Chief Economist Bob Costello said. Costello noted that it was the largest month-to-month increase since January 2005.

"Not only did truck tonnage increase due to solid manufacturing output in December, but also from some likely inventory restocking. Inventories, especially at the retail level, are exceedingly lean, and I suspect that tonnage was higher than expected as the supply chain did some restocking during the month." he said.