The American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index rose 5.9% over the previous year, the largest annual increase since 1998.

Tonnage for December 2011 was 10.5% higher than the previous year. November tonnage was up 6.1% over the same month last year.

Tonnage rose 6.8% from November to December 2011. This latest gain put the SA index at 124.5 (2000=100) in December, up from 116.6 in November.

"While I'm not surprised that tonnage increased in December, I am surprised at the magnitude of the gain," says ATA chief economist Bob Costello.. 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," Costello says. "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."

According to Jeffries & Company equity analyst Peter Nesvold, this increase is "likely reflecting stronger chemical loads (which is heavier freight and is being boosted by the surge in fracking demand) and the unseasonably warm winter, which appears to have aided some construction activity."