As U.S. emissions standards grow stricter, carmakers appear to be keeping pace thus far.
Cars and light-duty trucks built for the 2012 model year beat EPA environmental standards, the Los Angeles Times reports.
Overall, carmakers achieved fleet-average emissions for 2012 of 286 grams of carbon dioxide per mile--9 grams less than the EPA standard specified in the Corporate Average Fuel Economy (CAFE) regulations set by the Obama administration for model years 2012 through 2016.
Average fuel economy was 23.6 mpg, up from 22.4 mpg the previous model year, showing progress toward the target of 54.5 mpg set in the second phase of standards, which governs model years 2017 through 2025.
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For reference, that "54.5 mpg" in the CAFE standards actually translates to an EPA gas-mileage rating of about 42 miles per gallon on the window sticker.
However, the progress isn't as straightforward as it seems.
While consumers can buy more fuel-efficient cars, the numbers used to determine compliance with regulations, don't necessarily indicate real-world efficiency improvements.
That's because certain carmakers have met their goals by buying credits from other manufacturers.
In its report, the EPA noted that without credits, average carbon-dioxide emissions would be 296 grams per mile--1 gram above the mandated standard.
The Safe Climate Campaign--a Washington-based advocacy group--told the Los Angeles Times that only one carmaker, Honda, would have complied with the CAFE standards without credits.
Manufacturers can earn credits for deploying certain technologies, or building vehicles with emissions lower than the standards, and then sell those credits to other companies.
General Motors, for example, was set a standard of 369 grams of CO2 per mile for its light-truck fleet.
Without credits, the GM trucks averaged 397 grams, but the Detroit carmaker was able to bring that number down to 366 grams by purchasing credits from other carmakers.
The alternative for some carmakers, meanwhile, is simply to pay noncompliance fees if they don't meet EPA standards.
Doing so, however, may carry a publicity downside that automakers like to avoid--much as companies worked hard not to pay "gas-guzzler taxes" in previous years.