Although EPA gas-mileage ratings may or may not be achievable in real-world driving conditions, they're a good relative benchmark.

They're also a very public encouragement to carmakers to make more fuel-efficient cars.

Hyundai, whose new 2011 Elantra compact model is rated at 40 mpg highway for all sedan models (the Touring is a carryover from the previous generation), has now stepped up its challenge to other makers.

Two months ago, the company began breaking out sales totals for every car it sold that got 40 mpg or better, starting with November sales figures. And it all but dared other carmakers to do the same, though we're not aware of any that took Hyundai up on its challenge.

2011 Hundai Sonata Hybrid, La Jolla, California, October 2010

2011 Hundai Sonata Hybrid, La Jolla, California, October 2010

Now, Hyundai is going further, saying it will include in its monthly sales data a sales-weighted average gas mileage. That is, its average mileage will be higher if it sells lots of Elantras and Sonata Hybrids, but lower if it sells high volumes of the less efficient Genesis and Equus large luxury sedans.

For January, the company says, the sales-weighted average for all models it sells was 34.7 mpg. That breaks down into 36.4 mpg for its cars, and 29.8 mpg for minivans and crossovers (it does not sell pickup trucks).

Hyundai is making an aggressive push to raise the fuel efficiency of all its models, including a flat ban on any V-6 engines for the midsize Sonata sedan and the compact Tucson crossover.

"In 2008, Hyundai had committed to achieve a CAFE level of at least 35 mpg by 2015," said Hyundai Motor America CEO John Krafcik. "Now we can confidently project achieving a 35 mpg average several years early."

"With 2025 CAFE targets being discussed in the 47-to-62 mpg range," he continued, "Hyundai's fuel economy may provide some confidence to policy-makers that this industry can achieve remarkable fuel efficiency gains, without compromising vehicle sales, appeal, value, or customer satisfaction."