American Trucking Associations’ seasonally adjusted For-Hire Truck Tonnage Index surged 6.8 percent in December from November and was 10.5 percent higher than December 2010.

Last year, tonnage increased 5.9 percent over the previous year, which was the biggest annual rise since 1998, according to ATA.

The December year-over-year gain was the largest since July 1998, ATA said.

The not seasonally adjusted index measuring tonnage actually hauled by fleets rose 0.8 percent in December from 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. He said 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 said.