It just keeps rising: Average gas mileage for new cars has once again hit a new high in the U.S.

Statistics kept by the University of Michigan's Transport Research Institute (UMTRI) show sales-weighted MPG of 24.8 mpg in May.

That contrasts with 24.6 mpg in March, and a rise from 24.5 mpg in January.

When report authors Michael Sivak and Brandon Schoettle began taking figures in October 2007, the average gas mileage of new cars was just 20.8 mpg, illustrating the constant improvements carmakers have made to improving fuel efficiency--and the public for buying the new cars.

The figures are calculated from the monthly sales of individual models of light-duty vehicles--cars, SUVs, minvans and trucks.

When this data is paired with the EPA window sticker gas mileage of each vehicle sold, it's possible to determine the average.

So while the overall number seems low--under 25 mpg is certainly nothing special these days--it's much more representative when you consider just how many sub-20 mpg trucks and mid-twenties minivans are helping bring down the average.

And even those vehicles have made significant advances over the past half-decade--as the lowest lows creep upwards, so too will the overall sales-weighted efficiency.

Should buyers switch to the most economical models in even greater numbers, sales-weighted MPG will rise even further.

UMTRI also measures what it calls the 'Eco-Driving Index', or EDI.

Two EDI measurements are calculated--one based on the average fuel used per distance driven in new vehicles; the other for distance driven by an individual driver.

While distance driven has remained fairly static since data recording started (98 percent of the October 2007 figure), fuel used per distance driven has dropped by a significant 17 percent.

So we may be driving as much as we were five or six years ago, but the fuel we're using has dropped by quite a volume.

And we'll keep seeing that figure drop--and average economy rise--in the future.

By how much? Well, that's really up to you guys...


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