American Trucking Associations’ advanced seasonally adjusted For-Hire Truck Tonnage Index decreased 1.2% in July after falling 2% in June. In July, the index equaled 109.8 compared with 111.1 in June.

“Softness in tonnage over the last few months is due more to supply constraints, rather than a big drop in freight volumes,” said ATA Chief Economist Bob Costello in a press release. “Not only are there broader supply chain issues, like semiconductors, holding tonnage back, but there are also industry specific difficulties, including the driver shortage and lack of equipment. For-hire truckload carriers are operating fewer trucks than a year earlier. It is difficult to haul significantly more freight with fewer trucks and drivers.

Retail sales and housing starts, both large drivers of truck freight, retreated in July, although both rose on a year-over-year basis, Costello said.

June’s reading was revised down to -2% from 1.5%.

Compared with July 2020, the SA index fell 2.9%, which was the first year-over-year drop since March. In June, the index was flat from a year earlier. Year-to-date, compared with the same seven months in 2020, tonnage is down 0.2%.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 111.9 in July, 3.2% below the June level (115.6). In calculating the index, 100 represents 2015. ATA’s For-Hire Truck Tonnage Index is dominated by contract freight as opposed to spot market freight.

Trucking serves as a barometer of the U.S. economy, representing 72.5% of tonnage carried by all modes of domestic freight transportation, including manufactured and retail goods. Trucks hauled 11.84 billion tons of freight in 2019. Motor carriers collected $791.7 billion, or 80.4% 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 5th day of each month. The report includes month-to-month and year-over-year results, relevant economic comparisons, and key financial indicators.