American Trucking Associations’ advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index increased 2.7% in May, following a revised 1.7% drop during April. In May, the index equaled 139 (2000=100), up from 135.3 in April. The all-time high was 144 in February.

Compared with May 2015, the SA index jumped 5.7%, which was up from April’s 2.4% year-over-year gain. Year-to-date, compared with the same period in 2015, tonnage was up 4%.

“Following two consecutive decreases totaling 6%, May was a nice increase in truck tonnage,” said ATA Chief Economist Bob Costello. “Better consumer spending in April and May certainly helped, but economic growth remains mixed and I’d expect the recent choppy pattern in tonnage to continue for the next quarter or two.

“We recently received good news on the inventory cycle, with the total business inventory-to-sales ratio declining for the first time in nearly a year. While one month doesn’t make a trend, this was good news for the trucking industry,” he said.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 138.9 in May, which was 2.4% above the previous month (135.6).

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.