The U.S. Environmental Protection Agency recently released its annual report, "Light-Duty Automotive Technology, Carbon Dioxide Emissions, and Fuel Economy Trends: 1975 through 2010." For the sixth consecutive year, the EPA is reporting a decrease in average carbon dioxide (CO2) emissions and a slight increase in the average fuel efficiency for new cars and light-duty trucks. For 2009, the most recent year for which the EPA has final data from automakers, the average CO2 emissions from new vehicles were 397 grams per mile and the average fuel economy value was 22.4 mpg. The findings confirm that, beginning in 2005, average CO2 emissions decreased and fuel economy increased each year. Since 2004, average CO2 emissions have decreased by 14 percent and average fuel economy has increased by 16 percent. The positive trend reversed a long period of increasing CO2 emissions and decreasing fuel economy that ran from 1987 to 2004.

This would seem to be encouraging news that would have polar bears high-fiving Eskimos and penguins doing back flips. Dig a little deeper into the report, however, and a different reality is revealed.

It turns out that the good news is more a function of consumers buying a different mix of vehicles in model year 2009 than individual models becoming more fuel efficient and emitting less CO2 from their tailpipes. According to the report, model year 2009 was a "year of considerable turmoil in the automotive market."

Production numbers in 2009 totaled just 9.2 million units, the lowest of any year since the report's database began in 1975. Those numbers represented a 34 percent drop in total vehicle production compared to 2008 and 40 percent against 2007. So unexpected was this situation that the final 2009 values for CO2 emissions were lower and fuel economy was higher than the previous year's report had predicted.

Fewer Trucks Sold, Better Environmental Results

The EPA told AOL Autos that there were many factors at play in increasing fuel economy and decreasing CO2, with the most important being that the truck market share was eight percent lower in 2009. Light trucks-which include sport-utility vehicles, minivans and vans, and pickup trucks-accounted for 40 percent of all vehicle sales, its lowest level since 1995.

Just as fewer light-truck sales had a positive effect on the 2009 numbers for CO2 and fuel economy, the high truck sales numbers of the past sent the numbers in the opposite directions, with higher CO2 emissions averaging between 120 to 140 grams per mile and six to seven mpg lower fuel economy than cars. These factors contributed to much of the increase in CO2 emissions and decline in fuel economy of the overall new light-duty vehicle fleet from 1987 through 2004.

Better Fleet Fuel Economy Means Lower CO2 Emissions

In 2009, all but one of the 14 largest automakers increased their fuel economy, which in turn decreases CO2 emission rates. In addition, seven manufacturers increased their average fuel economy numbers by one mpg or more.

Toyota had the lowest fleetwide adjusted composite CO2 emissions (and the highest fuel economy performance), followed by Hyundai and Honda. Chrysler was the one manufacturer that did not improve its numbers in 2009 and it had the highest CO2 emissions and lowest fuel economy, followed by Daimler and Ford.

Toyota had the biggest improvement in adjusted CO2 and fuel economy performance from 2008 to 2009. It reduced its CO2 emissions by 10.3 percent while increasing its fuel economy by 11.4 percent. Nissan followed with a reduction in CO2 emissions by 7.1 percent and improving fuel economy by 7.8 percent. Ford was the most improved domestic manufacturer with a reduction in CO2 emissions by 4.8 percent and improving fuel economy by 5.2 percent.

Less Power + Lower Weight = Better Numbers

Model year 2009 saw the largest annual decrease in vehicle weight and power since 1980. Vehicle weight averaged 3917 pounds-a decrease of 168 pounds (about four percent) from 2008-and the lowest average weight since 2001. The average weight of a truck dropped by roughly 100 pounds and the average weight of a car by 60 pounds; the remaining difference was due to lower market share for trucks.

Along with weight, average power for the fleet dropped, too. In 2009, the average vehicle had 208 horsepower, the lowest number since 2003. Average horsepower dropped by 11 hp (about five percent). Interestingly, four-cylinder engines increased their share of the market from 38 percent in 2008 to 51 percent in 2009-and comprised nearly 70 percent of the car market. Speed freaks need not fret, however: The estimated 0-to-60-mph time remained constant at 9.7 seconds.

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