Average per-vehicle incentives from U.S. auto makers slid 8.6 percent in March from February and declined 17 percent from a year earlier, according to car-shopping site Edmunds.com.

“These latest numbers show by far the biggest February-to-March incentives decline since Edmunds.com started tracking (the metric)  in 2002,” said Edmunds.com analyst Ivan Drury.

Drury said the decline was most likely a result of a projected 26 percent month-over-month sales jump in subcompact and compact cars. Those vehicles typically have a much lower  incentives than large trucks and sports-utility vehicles, Drury said.

General Motors Co.  spent 8.6 percent less on incentives from a year earlier, and the figure was 17 percent lower on a sequential basis.

Director Jessica Caldwell said the costly incentives GM spent inthe first two months of the year slid sharply in March and will translate to lackluster retail sales.

“The industry will be carefully watching GM’s performance this month to see if March was an aberration or the start of a downward trend,” said Caldwell.

On a year-to-year basis, the six top auto makers reported lower incentives. Toyota Motor Corp.  spent 27 percent less on incentives, while the figure dropped 3.2 percent for Honda Motor Co.  Year earlier figures for both were a record for their incentive spending, according to Edmunds.com.

The industry gave out an average $2,346 for each vehicle sold last month, down $469 from last year and off $220 from February.

Among segments, large cars again had the highest average incentives, followed by premium luxury cars. Subcompacts had the lowest, with sport cars next.