American motorists stand to save billions of dollars a year from higher fuel economy vehicles now on the road, the Environmental Protection Agency said on Wednesday.

Fuel economy for new light-duty vehicles in the United States reached an all-time high in the 2013 model year, averaging 24.1 miles per gallon, up 0.5 mpg on the year, the EPA said in an annual report. At the same time, average carbon dioxide emissions fell to a record low.

U.S. fuel economy has increased in eight of the last nine years and is up nearly 5 mpg since 2004, the agency said.

The EPA said recent improvements in part reflected automakers' rapid adoption of more efficient technologies such as gasoline direct injection engines, turbo chargers and advanced transmissions. 

“Today’s announcement points to the greatness of American ingenuity and the strength of our auto industry," EPA administrator Gina McCarthy said.

The EPA estimates that a plan to double fuel economy by 2025 will save the average American family more than $8,000 in fuel costs per vehicle.

The agency said Mazda vehicles averaged the highest fuel economy, at 28.1 mpg, and lowest greenhouse gas emissions from the 2013 car and light truck fleet.

Nissan logged the biggest improvement in average fuel economy and greenhouse gas reductions, posting fleet-wide fuel economy of 26.2 mpg, up 8.7 percent on the year.

"The realization of this accomplishment came in part due to the introduction of three all-new fuel-efficient models for the 2013 model year - Altima, Pathfinder and Sentra," Nissan Group said in a statement.

Sport utility vehicles, long castigated as gas-guzzlers, achieved the greatest improvement by class, the EPA said.

Assuming gas prices of $3.50 per gallon, the 3-mpg jump in passenger car fuel economy from 2008 to 2013 would save a typical driver over $300 in the first year, the Natural Resources Defense Council estimated.