The WardsAuto Fuel Economy Index held steady for the third straight month in May, as U.S. light-vehicle sales matched the record average fuel-economy rating of 24.3 mpg (9.7 L/100 km) set in March and equaled in April.

The May FEI score represented a 1% increase over year-ago and a 16% gain on the base rating established in fourth-quarter 2007.

But while the score remained the same, the market continued to shift away from the segments with the highest average fuel economy to those with lower ratings, raising doubt about the industry’s ability to maintain its current record-high efficiency level.

Cars made up less than 50% of LV sales for the second consecutive month in May, with a 49.2% share, the vehicle type’s lowest since December. However, the downturn was offset by an uptick in average fuel economy, which rose to a record 28.1 mpg (8.4 L/100 km).

While all four car segments lost share from April to May, three improved their FEI ratings.

Midsize-car sales accounted for 20.8% of LV sales while averaging 28.2 mpg (8.3 L/100 km), up 5% from year-ago. Luxury and large cars both achieved record FEI ratings, averaging 24.5 mpg (9.6 L/100 km) and 21 mpg (11.2 L/100 km), respectively.

Small-cars share fell slightly from April to May, but the segment remained atop the WardsAuto index with a 29.8 mpg (7.9 L/100 km) rating, even with April and up 1.1% from year-ago. Light trucks tracked by the index maintained a record 20.3 mpg (11.6 L/100 km) FEI rating for the third straight month.

May was the first month since last July that all four truck segments grew their month-on-month share.

Cross/utility vehicles accounted for 24.8% of LV deliveries, while attaining a segment-record 22.4 mpg (10.5 L/100 km), up 1.1% from prior-year. This offset, in part, the share increase of the three segments with the lowest FEI scores – vans, SUVs and pickups.

SUV share climbed to a 5-month high of 6.8% in May, earning a record 17.7 mpg (13.3 L/100 km) index score for the month, the second-lowest segment rating behind pickups.

Van deliveries made up 5.8% of LV sales, the segment’s largest share since August, and averaged 20.6 mpg (11.4 L/100 km).

Pickup sales were the biggest threat to the industry’s current record fuel economy. The lowest-rated segment on the FEI gained share for the second straight month, accounting for 13.5% of May deliveries, and expected to outpace industry growth through the summer as the housing and construction sectors continue to warm up.

While improving fuel-economy in other market segments so far has staved off the downward effect of escalating pickup sales, it’s likely the trucks' growing share and 16.8 mpg (14 L/100 km) rating soon will knock the industry FEI rating off its current record-setting perch.

The WardsAuto Fuel Economy Index through May reached 24.3 mpg (9.7 L/100 km), up 1% from year-ago.

jsousanis@wardsauto.com