The sales-weighted average fuel economy of new cars and trucks sold in the U.S. declined last month, although it remains high overall.

Average window-sticker fuel economy for new vehicles in April was 25.2 mpg, representing a decrease of 0.2 mpg from March.

This information comes from the University of Michigan Transportation Research Institute (UMTRI), which tracks fuel economy on a monthly basis.

DON'T MISS: Plug-In Electric Car Sales In Apr: Pace Continues Steady: FINAL UPDATE

April's sales-weighted average was down 0.6 mpg from the peak reached in August 2014.

However, overall fuel economy is still up 5.1 mpg from October 2007--the first month of monitoring by UMTRI researchers.

In addition, average fuel economy for the first seven months of the current model year--considered to begin in October 2014--is 25.3 mpg.

Gas pump

Gas pump

That matches the average figure for the entirety of the preceding model year, measured from October 2013 to September 2014.

The UMTRI also calculates an Eco-Driving Index, which estimates the average monthly emissions of greenhouse gases generated by an individual U.S. driver.

ALSO SEE: Green-Car Decline: Combined Hybrid, Electric Sales Started Falling Last June

For February--the most recent month with available data--the index was 0.82, the same as the value for January. Lower numbers equal lower estimated emissions in this case.

That value indicates that the average new-vehicle driver generated 18 percent lower emissions in February 2015 than in October 2007.

UMTRI researchers attribute April's drop in average fuel economy to increased sales of trucks and SUVs.

Non-ethanol gasoline pump, with Six Month Road Test Hyundai Veloster

Non-ethanol gasoline pump, with Six Month Road Test Hyundai Veloster

SUV sales in particular have been robust for several months, something many analysts have attributed to the current low average price of gasoline.

Yet while consumer trends may drive the average fuel economy of vehicles sold in a given month down, it should continue to trend upward over the long term.

RELATED: Gas Mileage Rules For 2025 Could Be Lowered If Buyers Stick With SUVs

That's because carmakers will have to continue improving fuel economy across their lineups to meet Corporate Average Fuel Economy (CAFE) standards.

These standards mandate a fleet average of 54.5 mpg by 2025, which is equivalent to about 40 mpg on the window sticker.


Follow GreenCarReports on Facebook, Twitter, and Google+.