American Trucking Associations’ advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index jumped 7.1% in August, following a 0.5% gain during July. In August, the index equaled 149 (2000=100), up from 139.1 in July.

Compared with August 2016, the SA index surged 8.2%. In July, the index rose 2.7% on a year-over-year basis. Year-to-date, compared with the same eight months in 2016, the index is up 2.1%.

As part of this report, ATA also revised its July increase in the index upward to a 0.5% gain from the previously reported 0.1% increase.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 156.4 in August, which was 10.5% above the previous month (141.6).

“Tonnage was stronger than most other economic indicators in August and more than I would have expected,” said ATA Chief Economist Bob Costello. “However, prep work for the hurricanes and better port volumes likely gave tonnage an added boost during the month.

“I suspect that short-term service disruptions from when the storms made landfall, as well as the normal ebb and flow of freight, could make September weaker and tonnage will smooth out to more moderate gains, on average,” he said.

Trucking serves as a barometer of the U.S. economy, representing 70.6% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled nearly 10.5 billion tons of freight in 2016. Motor carriers collected $676.2 billion, or 79.8% 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.