Is 40 mpg the new 30? Reading between the ad lines

In the world of car advertising, "40" is the new "30." And with gas prices still hovering around $4 a gallon, and threatening to rise, many consumers are looking toward more fuel-efficient vehicles to reduce their expenses. And a majority of car shoppers are willing to pay extra to save fuel, but as our latest analysis shows, some special-edition fuel misers are not worth the premium.

Several years ago, General Motors kicked off a wave of fuel economy-focused advertising that continues to gain momentum. In responding to heavy criticism that its cars couldn't match the gas mileage of import competitors, GM began touting the number of it models that were EPA-rated at more than 30 mpg on the highway, drawing attention away from the federal city and overall mpg numbers. The fact that GM made four redundant versions of almost every model became a true marketing advantage

Other automakers have picked up the mantle, with advancing technology boosting fuel economy even further. Now 40 has indeed become the new 30.

• Ford has been advertising that its new subcompact Fiesta gets 40 mpg on the highway, as does the new Ford Focus. (See ad.)
• Hyundai has been advertising its Sonata Hybrid, Elantra, Veloster, and Accent using their 40 mpg highway ratings. (See ad.)
• Now Honda is weighing in with ads touting the new Civic's 41 mpg highway rating. (See ad.)
• And of course, GM has followed up its earlier 30 mpg ads with new ads touting the "40-mpg" Chevrolet Cruze. (See ad.)

Not only do these numbers just reflect highway mileage, they only apply to certain versions of the cars. They come with additional equipment including things like air spoilers, shutters in the grille that improve aerodynamics at high speeds, and low-rolling-resistance tires, which we have sometimes found reduce braking and handling grip.

In the latest automotive survey by the Consumer Reports National Research Center, 58 percent of respondents told us they would pay more for a car that gets better mileage. That's fine, but if you're going to spend more, don't be mislead by false claims.

To clear 40 mpg on the highway, you have to spring for Ford's SFE (super fuel economy!) package on the Focus and even the subcompact Fiesta, or buy the new Honda Civic in HF trim. Chevrolet requires you not only to opt for the special Cruze Eco trim, you also have to order a manual transmission to get the advertised 42 mpg on the highway.

All these trim packages come at a cost: The SFE package runs $695 on the Fiesta and $495 on the Focus. The Civic HF costs about $800 more than the Civic LX. And the Cruze Eco costs the same as a mostly comparable Cruze 1LT (about $900 more than a base Cruze), but it lacks an automatic transmission. Adding the automatic costs another $925, but then you get just 36 mpg on the highway.

Of the current, non-hybrid models that advertise 40 mpg or more on the highway, only the Hyundai Elantra doesn't require you to pay extra for a special edition. And in our own real-world fuel economy testing, we've found some other models that return 40 mpg on the highway, even if their advertised EPA highway ratings are lower. They include the Mazda3, and the Toyota Corolla and Yaris.

In days ahead, we'll run the numbers on some of these special-edition models to see which ones may be worth the extra price.

Related:
40 mpg dollars and sense: Are the Ford Focus, Fiesta SFE models worth the money?
40 mpg dollars and sense: Chevrolet Cruze Eco saves fuel--as long as you shift yourself
40 mpg dollars and sense: Honda Civic HF may save fuel, but doesn't really save money

See our guide to fuel economy.

—Eric Evarts