By Warren Brown
Sunday, October 21, 2007

Caution: Federal gas mileage estimates for 2008-model cars and trucks will be 12 to 30 percent lower than those for 2007 models.

For gas-electric hybrid cars, such as the Toyota Prius, the drop will be 20 to 30 percent. For example, the city mileage rating for the 2008 Prius falls to 48 miles per gallon from 60 mpg for the 2007 model. (Current-generation hybrid cars get better mileage in stop-and-go city traffic, where their electric motors do most of the work. Their gasoline engines carry the load on the highway, which means their highway fuel efficiency often is lower than the city average.) On the highway, the 2008 Prius will get 45 mpg, down from its federal highway estimate of 51 mpg last year.

The new, lower mileage ratings do not mean automotive technology is moving backward. They come because the federal government's testing for vehicular fuel efficiency has moved forward and become more realistic.

Under rules approved by the Environmental Protection Agency in 2006 and now being used in evaluations of 2008-model cars and trucks, the government considers extreme temperature changes, varying road grades, the use of power-sucking devices such as air conditioners and aggressive driving in testing for fuel efficiency.

As has been the case in the past, the new tests are conducted in a laboratory environment. But they go far beyond the EPA's old fairytale mileage approach, which involved running cars and trucks at steady legal and lower speeds on dynanometers in mild ambient temperatures.

Still, consumers should be advised that the EPA's new testing procedures do not guarantee that the mileage ratings they see on window stickers will be the same miles per gallon they get on the road. No laboratory test can make that guarantee. That means actual mileage, up or down, will continue to vary from mileage on the federal fuel economy label.

That raises the question: Why bother?

The answer is that past federal mileage ratings were so out sync with real-world experience, they more often misled consumers than informed them. The new testing procedures are meant to bring truth in advertising more in line with truth in driving. And that means we are likely to see fewer car companies boasting about their "30 mpg and over" new-vehicle fleets in 2008. That is a good thing.

The revamped mileage-rating system should help consumers make better cost-benefit analyses when buying new vehicles. For example, is it really worth it to buy a gas-electric hybrid vehicle that gets marginally better, or lower, fuel economy than, say, a smaller, traditional gasoline-powered vehicle that has a lower overall purchase and operating cost and possibly a better trade-in value?

Why the concern about trade-in value? It's simple. The auto industry has been downright reticent about what will happen to the value of used gasoline-electric hybrids with old nickel-metal-hydride batteries that will be made obsolete by more efficient lithium-ion and lithium-polymer battery packs.

I have asked foreign and domestic car companies if we will be able to replace the nickel-metal-hydride packs with lithium batteries when lithium automotive batteries become available in five years, possibly less. All of my queries on the matter have gotten negative answers.

What, then, will happen to the resale value of the nickel-metal-hydride hybrids? No one seems to know. Or if they know, they are not willing to give a definitive answer, which leads me to believe that today's hybrids will be as valuable at resale as yesterday's laptops.

Might it not be better then to use the EPA's new, tougher mileage rating system to choose a high-mpg gasoline or diesel-powered car, or one powered by an alternative fuel, and dispense with the worry about which batteries will replace current batteries down the road, whether those batteries would be interchangeable, and what would be the environmental and financial disposal cost of those batteries once they are depleted? Should we not consider those things alongside fuel-efficiency ratings?

At least, the EPA has moved to take some of the guesswork out of buying new vehicles. Along with its more accurate mileage ratings, it is offering a simplified mileage statement label that helps consumers compare the fuel economy of vehicles in the same size and performance categories. That is a very good thing, now available in detail, including a full vehicle guide, at http://www.fueleconomy.gov/feg/FEG2008.pdf.

For those of you who want more information on the government's new testing procedures -- exactly what those testing protocols are and the rationale for using them -- go to http://www.epa.gov/fueleconomy.