American Trucking Associations’ advanced seasonally adjusted For-Hire Truck Tonnage Index was unchanged in December, following a jump of 3.5% during the previous month. In December, the index equaled 136.8, which tied November as the all-time high.

Compared with December 2013, the SA index increased 5.2%, which was the largest year-over-year gain in 2014. For the entire year, tonnage was up 3.5%.

“Economic data was mixed in December, with retail sales down 0.9% and factory output up 0.3%, so tonnage was in-between those two readings, which are two large drivers of truck freight,” said ATA chief economist Bob Costello. “Overall, 2014 was a good year for truck tonnage with significant gains throughout the year after falling 4.5% in January alone.”

Costello said that in December, tonnage was 10.2% above January.

Trucking serves as a barometer of the U.S. economy, representing 69.1% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 9.7 billion tons of freight in 2013. Motor carriers collected $681.7 billion, or 81.2% of total revenue earned by all transport modes.

To view the full ATA report, click here.