American Trucking Associations' advanced seasonally adjusted For-Hire Truck Tonnage Index declined 1.1% in March after easing 0.8% in February. In March, the index equaled 110 (2015=100), down from 111.2 in February.

ATA revised the February decline from the originally reported 2.6% to 0.8%.  

Compared with March 2017, the SA index jumped 6.3%, which was below February's 7.7% year-over-year gain, but still well above 2017's annual increase. For all of 2017, the index increased 3.8% over 2016. In the first quarter of this year, tonnage rose 0.9% and 7.4% from the previous quarter and a year earlier, respectively.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 114.6 in March, which was 12.9% above the previous month (101.5).

"Despite a softer March and February, truck freight tonnage remains solid as exhibited in the year-over-year increase of 6.3%," said ATA Chief Economist Bob Costello. "While I expect the pace of growth to continue moderating in the months ahead, if for no other reason than year-over-year comparisons will become more difficult as tonnage snapped back in May of 2017, the levels of freight will remain good going forward."

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.