American Trucking Associations’ advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index decreased 1.8 percent in August after increasing 1.9 percent in July. In August, the index equaled 112.9 (2015=100), down from 115 in July.

Compared with August 2017, the SA index rose 4.5 percent, down from July’s 8.6 percent year-over-year increase. Year-to-date, compared with the same period last year, tonnage increased 7.6 percent, far outpacing the annual gain of 3.8 percent in 2017.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 120.4 in August, which was 5 percent above the previous month (114.6).

“Truck freight remained solid in August despite the monthly decline,” said ATA Chief Economist Bob Costello. “However, the year-over-year increase was the smallest since July 2017. The deceleration in the year-over-year increases has begun due to more difficult year-over-year comparisons. It was a year ago when freight began to surge. We should all expect smaller year-over-year gains going forward than we witnessed over the last year.”

Trucking serves as a barometer of the U.S. economy, representing 70.2 percent of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 10.77 billion tons of freight in 2017. Motor carriers collected $700.1 billion, or 79.3 percent 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.