For the first time, vehicles rated 25 mpg (9.4 L/100 km) or higher comprise more than one-third of light vehicles sold in the U.S. over a full year, according to the WardsAuto Fuel Economy Index.

The average fuel economy of LVs delivered in 2012 rose 4.8% from year-ago, improving on the ’12 model year’s (ended in September) comparison of 4.5%.

The Index’s total LV sales’ number excludes some light trucks that are not part of the Environmental Protection Agency’s corporate average fuel economy program.

The 2012 LV rating of 23.8 mpg (9.9 L/100 km) was a 1.1 mpg (0.5 km/L) improvement over the 2011 rating, and a 13.5% increase over the Index base rating of 20.9 mpg (11.2 L/100 km) set in fourth-quarter 2007.

LVs achieving less than 15 mpg (15.7 L/100 km) made up just 0.7% of calendar- year sales, compared with 2.8% in like-2011 and more than 8% of deliveries in the base period.

On the other end of the spectrum, LVs rated 40 mpg (5.9 L/100 km) doubled their penetration of the U.S. market, accounting for 3% of total deliveries, compared with 1.5% in the prior year.

The share of vehicles rated between 30 mpg (7.8 L/100 km) and 40 mpg surged 159% year-ago to 8.1%.

LVs rated 25 mpg (9.4 L/100 km) or higher accounted for 37.1% of 2012 sales, compared with 32% in 2011, and 16.1% in the base period.

Small cars helped move the Index needle, increasing their share to 19.6% compared with 18.4% year-ago, while also improving their FEI rating 3.8% to 29.5 mpg (7.9 L/100 km).

Midsize cars showed the largest gain on the Index of any segment, rising 4.7% to 27.2 mpg (8.3 L/100 km), while accounting for 21% of LV sales, compared with 19.3% in 2011.

Cross/utility vehicles remained the best-selling segment, making up 23.8% of U.S. LV deliveries, while averaging 22.2 mpg (10.6 L/100 km), a 2.9% improvement over prior year.

The light-duty pickup segment showed the second-best improvement on the FEI, while still earning the lowest index rating of any segment, 16.8 mpg (14.1 L/100 km), up 3.8% from 2011.

Only Large cars showed no improvement on the FEI, with a flat 20.2 mpg (11.6 L/100 km) rating. The segment became almost irrelevant, making up just 1.6% of all LV sales, its lowest annual share ever.

Toyota sat atop the FEI last year, lifting its average fuel economy 7.1% to 27.5 mpg (8.7 L/100 km), followed by Volkswagen, up 4.2% to 26.8 mpg (8.8 L/100 km).

Ford led the Detroit-based auto makers with a 22.5 index rating, a 6.7% improvement spurred by increased small-car sales and the introduction of several new hybrid and electric vehicles.

Jaguar Land Rover’s fleet of heavier SUVs and luxury sedans improved 5.8% over year-ago, but stayed at the bottom of the WardsAuto FEI with a 16.8 mpg (14 L/100 km) rating.

Chrysler and Daimler suffered the next lowest annual scores, with both auto makers rated at 19.8 mpg (12 L/100 km).

jsousanis@wardsauto.com