U.S. sales of medium- and heavy-duty trucks slumped 35.5 percent in January from a year earlier, to 17,118 units.
Sales of large trucks have been falling since April 2007. The latest monthly drop was the steepest in that period.
January sales fell by double digits in every class of medium- and heavy-duty truck. Class 8 sales dropped the least but still took a 23.2 percent tumble to 7,374 units. That drop ended seven consecutive months of rising sales of Class 8 trucks, the largest of the big rigs.
Sales of Class 6 trucks plunged 53.9 percent to 1,828 units. Class 4 sales fell 40.9 percent to 3,189. Class 5 sales slid 38.7 percent to 1,794. Class 7 sales dropped 37.2 percent to 2,933.
Freightliner claimed the top spot among truckmakers in January with sales of 4,169 vehicles, down 19.5 percent. Its Class 8 sales rose 3.7 percent to 2,527 units, helping Freightliner rise in the rankings from third place a year earlier.
International held onto No. 2, as its sales dropped 32.5 percent to 3,994 units. Ford Motor Co. fell to third in January large-truck sales from first in the year-ago month and for all of 2008. Ford's sales tumbled 46.6 percent to 3,528 units.
No other truckmaker sold more than 1,000 medium- and heavy-duty trucks in January.