Truck tonnage dropped 3.3% last month to its lowest level since November 2007, according to the American Trucking Associations (ATA).
ATA Chief Economist Bob Costello said the latest tonnage reading was "a significant setback.
"I’ve been concerned that the recent run-up in tonnage might not be sustainable, and clearly March’s figures confirmed that apprehension."
Costello continues to forecast a mild recession for the overall economy during the first half of 2008, but notes that March’s tonnage drop might suggest the economic contraction could be more severe than previously thought.
"Truck tonnage often leads both recoveries and recessions, and the latest contraction suggests the economy and trucking are not out of the woods yet."