The average fuel economy of new cars sold in the United States fell once more in September, although not by much.

Average new-car fuel economy continues to hover around 25 mpg, according to recent analysis.

The sales-weighted average window sticker fuel economy for new cars in September was 25.2 mpg, according to the University of Michigan Transportation Research Institute (UMTRI).

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That represents a 0.1-mpg decrease in average fuel economy from August, which researchers attribute to low gas prices and increased sales of SUVs and pickup trucks.

September was the second month in a row that new-car average fuel economy decreased.

The 25.2-mpg figure also represents a 0.1-mpg drop from the same period last year.

2016 Honda CR-V

2016 Honda CR-V

Of the nine months of 2015 recorded so far, eight have shown decreases compared to the same months a year ago.

So far, the overall average for 2015 stands at 25.3 mpg--the same as 2014.

If that holds steady--or if average new-car fuel economy continues to decrease--2015 could be the first year that average fuel economy hasn't increased since UMTRI researchers began tracking it in October 2007.

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Fuel economy is down 0.6 mpg from the peak recorded in August 2014, but still higher by 5.1 mpg over the level when monitoring began.

Researchers also calculate a monthly Eco Driving Index, which estimates the average monthly greenhouse-gas emissions generated by individual U.S. drivers.

It takes into account both fuel economy and distance driven.

2016 Ford F-150

2016 Ford F-150

For July (the most recent month with available data), the index stood at 0.82--unchanged from June.

That's an increase from the 0.79 recorded in July 2014 (lower numbers are better).

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The July 2015 figure means the average U.S. new-car driver generated 18 percent lower emissions than in October 2007, but four-percent higher emissions than the record low reached in August 2014.

The decline in fuel economy for September "likely reflects the decreased price of gasoline," said researchers Michael Sivak and Brandon Schoettle.

That in turn, they said, produces "consequent increased sales of pickup trucks, SUVs, and crossovers."


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