The average fuel economy of light vehicles sold in the U.S. rose 4.5% over year-ago during the ’12 model year, the WardsAuto Fuel Economy Index reveals, while finishing 14% above the base index score set in fourth-quarter 2007.

The combined fuel economy for all LV deliveries during the traditional October-September model-year period reached 23.6 mpg (10 L/100 km), a full 1 mpg (0.4 km/L) increase over the ’11 industry score of 22.6 mpg (10.4 L/100 km) and 3.7 mpg (1.5 km/L) better than the base rating of 20.9 mpg (11.2 L/100 km).

The year-over-year increase came as a result of improved Environmental Protection Agency ratings for many ’12 models and a shift in the market toward smaller, more fuel-efficient segments.

Small-car sales, which were hampered for much of ’11 by tsunami-related supply issues, accounted for 19.3% of the ’12 volume, up from prior-year’s 18.3%, while earning a record 29.4 rating for the period.

Midsize cars accounted for 21.2% of deliveries, up from 19.8% in ’11, while inching up the index to 27.0.

The light-duty pickup segment was the lowest-rated sector on the index, earning a 16.8 score, while accounting for 13.4% of ’12 deliveries, down slightly from 13.8% in ’11.

Large cars showed the least improvement, up just 0.3% to 20.2 mpg (11.6 L/100 km), while making up just 1.6% of the market – the segment’s lowest share ever.

Cross/utility vehicles comprised the best-selling segment in ’12, with 23.7% of LV sales, while also sporting an index rating of 22.1, up 3.3% from ’11.

Toyota regained the top spot on the index, as it recovered from severe tsunami-related inventory issues. The auto maker’s average fuel economy rose 7.6% to 27.3 mpg (8.6 L/100 km). Hyundai finished second with 26.8 mpg (8.8 L/ 100 km), followed by Volkswagen and Kia, each at 26.7 mpg (8.8 L/100 km).

Ford led Detroit-based auto makers with a 21.8 index rating, ahead of GM’s 21.3 and Chrysler’s 19.7 – the only sub-20 score among the top seven auto makers.

Vehicles rated more than 20 mpg (11.8 L/100 km) on the index accounted for 70.1% of all ’12 deliveries, up from 64.4% in ’11. In the index’s base period, fewer than half the LVs sold were rated higher than 20 mpg.

Vehicles achieving more than 30 mpg (7.8 L/100 km) accounted for 10.3% of volume in ’12, a 285% increase from the prior model year.

The WardsAuto FEI rating for calendar 2012 was up 5.1% to 23.8 through September and likely will outpace entire 2011 by an even larger margin. A year-ago, the fourth-quarter sales mix was skewed toward less-fuel-efficient vehicles as a result of tsunami-driven small- and midsize-car inventory shortages.

jsousanis@wardsauto.com