The American Trucking Associations’ advanced seasonally adjusted For-Hire Truck Tonnage Index increased 2% in January, reflecting strong economic conditions in a traditionally soft month.

The index rebounded from December, which saw a slight decrease of 0.3%. It is up 8.8% over January 2017, beating the previous month’s 7.5% year-over year increase.

“Last month’s gain in tonnage fit with the anecdotal reports we have been hearing from fleets – that freight was solid in what is typically a softer month,” said Bob Costello,  ATA chief economist. “With the economy strong, the drivers of truck freight solid, and the inventory cycle in favor of motor carriers, I expect freight tonnage to remain robust in the months ahead.”

Trucking can serve as a measurement for the U.S. economy as a whole, according to ATA, as it represents 70.6% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled nearly 10.5 billion tons of freight in 2016 and carriers brought in $676 billion, or 79.8% of the total revenue earned by all transport modes.