ARLINGTON, VA — The amount of for-hire truck freight moved in the U.S. fell in April to its lowest level in a year, according to the American Trucking Associations.

Its seasonally adjusted For-Hire Truck Tonnage Index declined 3% from the month before following a revised gain of 0.4% in March.

The April index reading of 128.6 is the lowest level since April 2014. The all-time high of 135.8 was reached in January 2015.

Compared with April 2014, the index increased just 1% last month, well below the 4.2% year-over-year gain in March and the smallest one since February 2013. Year-to-date through April, compared with the same period last year, tonnage is up 3.8%.

The not seasonally adjusted index, which represents the change in tonnage actually hauled by the fleets before any seasonal adjustment, equaled 130.6 in April, 5.9% below the previous month reading of 138.7.

“Like most economic indicators, truck tonnage was soft in April,” said ATA Chief Economist Bob Costello. “Unless tonnage snaps back in May and June, (U.S. gross domestic product) GDP growth will likely be suppressed in the second quarter.”

Costello added that truck tonnage is off 5.3% from the high in January.

“The next couple of months will be telling for both truck freight and the broader economy. Any significant jump from the first quarter is looking more doubtful,” he said.

According to ATA, 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. It calculates the tonnage index based on surveys from its membership.