American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index increased 2% in January after falling 0.3% in December. In January, the index equaled 111.6 (2015=100), up from 109.4 in December.

ATA recently revised the seasonally adjusted index back five years as part of its annual revision. In addition, ATA re-indexed the seasonally adjusted and not seasonally adjusted tonnage indexes to 2015 = 100 back to 1973.

Compared with January 2017, the SA index jumped 8.8%, which was above December's 7.5% year-over-year gain. For all of 2017, the index increased 3.8% over 2016.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 106.9 in January, which was 0.4% above the previous month (106.5).

"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 ATA Chief Economist Bob Costello. "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 serves as a barometer of the U.S. economy, representing 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. Motor carriers collected $676.2 billion, or 79.8% 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.