The numbers are in, and it turns out that 2013 was another record year for the average fuel economy of new vehicles.

Researchers at the University of Michigan Transportation Research Institute (UMTRI) say the sales-weighted average fuel economy of all new vehicles sold in the United States last year was 24.8 mpg, fully 1 mpg higher than the 23.8 mpg for 2012.

In fact, 2013's record performance is typical: Fuel economy has been improving year-to-year since UMTRI began collecting data in 2007.

Average fuel economy started strong in January at 24.5 mpg, and reaching 24.8 mpg in May.

The average dipped to 24.6 mpg in September, but climbed back to 24.8 mpg in December.

UMTRI's sales-weighted average covers all new vehicles, from hatchbacks and sedans to pickup trucks and SUVs, which is why the number is relatively low.

Three Old Gas Pumps Near Waldo, Ohio, by Flickr user The Upstairs Room

Three Old Gas Pumps Near Waldo, Ohio, by Flickr user The Upstairs Room

Fuel-efficiency numbers were available for 99.8 percent of new vehicles sold, according to the university. Model years were assumed to run from September of the previous year to August of the calendar year.

The university also calculates what it calls the Eco-Driving Index, which estimates the monthly greenhouse-gas emissions produced by the average individual U.S. driver.

The index--based on gas mileage and miles driven--was at 0.80, compared to 0.79 for 2012. Overall, it shows a 20 percent reduction in emissions from each new-car driver compared to the starting point of October 2007, which is set at 1.0 on the index.

The continuous improvement in fuel economy isn't surprising, as automakers try to keep pace with more stringent fuel-efficiency requirements.

The EPA and NHTSA announced a stricter set of rules for model years 2012 to 2016 back in April 2010, and even more stringent rules will take effect for model years 2017 through 2025.

In addition to improvements to internal-combustion fuel-economy, the 2013 average was slightly boosted by growing sales of plug-in electric cars, which in 2013 were nearly double the previous year's total and are expected to rise again in 2014.


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