The drop in U.S. Class 8 truck sales in March marked two consecutive years of monthly decline for the segment.
Sales in March fell 10.9 percent to 11,138 units compared with the same month a year ago.
Low-volume truckmaker Western Star, owned by DaimlerChrysler, posted the steepest Class 8 percentage drop in March. Its sales plunged 62 percent to 90 units.
Volvo had the second-largest percentage drop: 29.2 percent to 943 units.
Kenworth, which is owned by Paccar Inc. of Bellevue, Wash., bucked the Class 8 segment's downward trend, with sales up 36.3 percent to 1,511 units.
Class 8 sales for the first three months of the year were down 18.9 percent to 28,026 units.
Combined medium- and heavy-duty truck sales were down 21.1 percent in March to 26,485 units. Sales for the first three months of the year for these segments were down 21.9 percent to 69,754 units.