American Trucking Associations’ seasonally adjusted For-Hire Truck Tonnage Index dropped 0.9% in November, erasing half of the 1.8% gain from October.

The index equaled 134.3, down from the 135.5 in October and 1.1% below the all-time high of 135.8 from January of this year. Year-to-date through November, truck tonnage is up 2.7% compared to the same period a year ago.

Rising inventories in the supply chain as well as weak factory output in recent months are to blame for the subdued reading, according to ATA.

“Tonnage gave back half of the gain in October, highlighting weakness in factory output and new fracking activity, as well as a glut of inventories throughout the supply chain,” explained Bob Costello, ATA chief economist. “With year-over-year gains averaging just 1.2% over the last three months, there has been a clear deceleration in truck tonnage."

Compared with November 2014, the seasonally adjusted index increased only 0.2%, the smallest year-over-year gain since February 2013.

“Looking ahead, I remain concerned about the high level of inventories throughout the supply chain,” said Costello. “We recently learned that inventories throughout the supply chain and relative to sales rose in October. This will have a negative impact on truck freight volumes over the next few months.”