Soft manufacturing numbers are affecting truck freight, with the American Trucking Associations' seasonally adjusted For-Hire Truck Tonnage Index rising only 1.1% to 132.1 in May following a 1.4% loss in April.

May’s number is 2.7% off of the all-time index high of 135.8 reached in January of this year. Compared with last May, the SA index increased 1.8%, which was less than last month’s 2.7% year-over-year gain and the smallest year-over-year gain since February 2013.

Year-to-date through May, truck tonnage is up 3.7% over the same period last year.

“The good news is that truck tonnage increased in May,” said Bob Costello, ATA chief economist. “But tonnage is certainly not strong at the moment as factory output is soft and there is an inventory reduction occurring throughout the supply chain.”

Without seasonal adjustment, the index equaled 133.1 in May, which was only 0.3% above April’s not-seasonally adjusted index.

“I believe the inventory correction should end this summer and truck freight, helped by better personal consumption, will accelerate,” said Costello. “Which is good because I think it is unlikely factory output will boost truck tonnage much until later this year or next year.”