American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index decreased 2.1% in July, following a revised 1.6% decline during June. In July, the index equaled 134.3 (2000=100), down from 137.1 in June. The all-time high was 144 in February.

Compared with July 2015, the SA index rose just 0.3%, the smallest year-over-year gain in 2016. In June, the year-over-year increase was 2.1%.Year-to-date, compared with the same period in 2015, tonnage was up 3.2%.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 138.2 in July, which was 2.7% below the previous month (142).

"On a monthly basis, tonnage has decreased in four of the last five months and stood at the lowest level since October during July," said ATA Chief Economist Bob Costello. "This prolonged softness is consistent with a supply chain that is clearing out elevated inventories.

"Looking ahead, expect a softer and uneven truck freight environment until the inventory correction is complete. With moderate economic growth expected, truck freight will improve the further along the inventory cycle we progress," he said.

Trucking serves as a barometer of the U.S. economy, representing 68.8% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled just under 10 billion tons of freight in 2014. Motor carriers collected $700.4 billion, or 80.3% 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.