EPA gas-mileage label (window sticker), design used starting in model year 2013Enlarge Photo
Car buyers remain aware that the real-world fuel economy of new vehicles may not match the ratings on their window stickers.
The year-old Volkswagen diesel scandal has also shown the vulnerability of laboratory emissions tests to deliberate cheating by manufacturers.
But the news isn't entirely bad.
Today's Environmental Protection Agency (EPA) fuel-economy labels are far more accurate than they were a decade ago, according to a recent study conducted by Consumer Reports.
The study is a followup to one conducted by the magazine in 2005, and it showed much better results than its predecessor.
The original study analyzed 303 vehicles from model years 2000 and 2006, and found that 274 vehicles (90 percent) delivered fuel economy that was lower than their EPA ratings.
Gas pumpEnlarge Photo
They averaged a difference of 3.3 mpg, or 10.3 percent.
In its new analysis, Consumer Reports found that the gap between EPA ratings and its own observed fuel economy had narrowed significantly.
The average difference is now 0.8 mpg, or 3.1 percent.
The new study found that 57 percent of vehicles had lower fuel economy than their EPA labels, but for more than 80 percent of those vehicles, the real-world results were within 1 mpg of the rating.
However, the accuracy of EPA labels seemed to depend on the type of powertrain.
Gasoline engines averaged fuel economy that was 0.7 mpg lower than EPA ratings, but diesel engines were on average 0.7 mpg higher.
2016 Toyota Prius Two EcoEnlarge Photo
Hybrid powertrains averaged 3.3 mpg lower fuel economy, although Consumer Reports noted that many owners report higher average fuel economy that's closer to EPA ratings.
The magazine attributes the increased accuracy of EPA labels to changes in testing procedures made in 2008.
Those changes were meant to account for a wider range of operating conditions, including more robust acceleration, air conditioning use, and colder temperatures.
Yet even with the new testing procedures, major gas-mileage discrepancies can still occur.
2013 Hyundai Elantra sedanEnlarge Photo
In 2012, Hyundai and Kia were found to have overstated fuel economy on 13 models, spanning model years 2011 through 2013.
The two automakers subsequently settled with owners for $395 million, and paid $300 million to the U.S. government in penalties.
In 2014, Ford was forced to lower gas-mileage and efficiency ratings on six models, and make small compensatory payments to owners—following an earlier lowering of its C-Max Hybrid ratings.
In the end, a Ford C-Max Hybrid originally rated at 47 mpg combined carried a twice-revised EPA rating of 39 mpg combined, far closer to actual owners' real-world results.
So while the accuracy of fuel-economy tests may have improved, regulators must always be on the lookout for potential issues, as well as for ways to further refine the process.