The American Trucking Assns. (ATA) reported a slight increase in June for its advanced seasonally adjusted (SA) For-Hire Truck Tonnage Index. The Index climbed 0.1% in June following a 2.1% jump in May.

In June, the SA index equaled 125.9 (2000=100) versus 125.8 in May. June 2013 is the highest level on record, ATA said. Compared with June 2012, the SA index surged 5.9%, which is robust, although below May’s 6.5% year-over-year gain. Year-to-date, compared with the same period in 2012, the tonnage index is up 4.7%.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 125.9 in June, which was 5% below the previous month (132.4).

“The fact that tonnage didn’t fall back after the 2.1% surge in May is quite remarkable,” said Bob Costello, ATA chief economist. “While housing starts were down in June, tonnage was buoyed by other areas like auto production which was very strong in June and durable-goods output, which increased 0.5% during the month according to the Federal Reserve.”

Costello added that auto sales helped push retail sales higher in June, helping the Index.

 “The trend this year is heavy freight, like autos and energy production, is growing faster than lighter freight, which is pushing truck tonnage up,” he said.