Valuation and forecast solutions provider Black Book’s Used Vehicle Retention Index registered 113.8 for March, a 0.6% decline from February (114.5) but a 1.7% improvement from March 2018 (112.0).

The index has reflected a late start to the spring selling season, dropping each month since November, analysts said. SUVs and luxury vehicles showed the largest declines in March, with minivans, compact to midsize cars, and small pickups showing modest gains. Market share changes reflect a continued shift away from cars and toward more utilities and trucks.

"While the economy continues to expand, higher supply of used vehicles and affordability issues have continued to become headwinds for the industry," said Anil Goyal, the firm’s executive vice president of operations. "The spring market is expected to provide a quick jolt to the market during April, but we expect the index will feel the effects from slower retail demand of new vehicles that could lead to higher incentives."

The Black Book Used Vehicle Retention Index is calculated using Black Book's published wholesale average value on two- to six-year-old used vehicles, as percent of original typically equipped MSRP. It is weighted based on registration volume and adjusted for seasonality, vehicle age, mileage, and condition.