The federal "Cash for Clunkers" incentive program did indeed spark light vehicle sales in July and August, and all but 3,000 to 5,000 vehicles would not have been traded in without the rebates, according to a study by Ball State University's Center for Business and Economic Research.

A little more than 690,000 vehicles were exchanged under the program with associated rebates of $2.88 billion, the Department of Transportation said, and Transportation Secretary Ray LaHood labeled the program wildly successful, "which if measured by the yardstick of vehicle sales...