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New MPG Labels: Fueling Debate & Controversy

New labels that are designed to provide a better comparison of how much fuel and energy that new vehicles will consume are a step in the right direction, but they tend to oversimplify the differences, particularly for electric cars and plug-in hybrids.

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The mandatory fuel-economy labels that are incorporated into the window sticker of every new vehicle always have been as much about bragging rights for auto manufacturers as they have been a definitive tool for anyone who shops for a car, SUV, pickup or minivan. But consumers have a new and more complicated label to deal with that’s designed to do a better job of helping them to compare the fuel efficiency and the long-term costs of operation for vehicles that have different fuel sources.

The radical makeover for the label is the result of automakers adding more vehicles that run on electricity and other alternative fuels. The new label, which was approved by federal regulators in June, is mandatory for 2013 model-year vehicles, and manufacturers can use them on new 2012 models as early as this fall.

Precisely what a vehicle’s new label measures and shows depends on its source of power. (See “Behind the Fuel-Economy Label.”) But the new labels for all vehicles—including gasoline-, diesel-, electric- and plug-in-hybrid-powered models—are more crowded than the current label is. In addition to information about fuel economy and annual fuel cost, both of which are on the current label, the new label adds information that allows you to compare tailpipe emissions, potential fuel-cost savings over a 5-year period, fuel consumption per 100 miles and driving range for some vehicles—most notably electric cars and plug-in hybrids.

Independent fuel-economy experts whom we interviewed say the new labels are a step in the right direction, because they give consumers more information about the fuel costs and emissions impact of their vehicles. But in trying to provide all of that information—and despite roughly 18 months of work by Environmental Protection Agency and National Highway Traffic Safety Administration—plenty of evidence suggests that the new labels in some cases will give consumers oversimplified, inflated or misleading information about the fuel economy and the environmental impact of the latest vehicles.

ELECTRIC COMPARISON. For the first time, electric cars and plug-in hybrids have a separate calculation of fuel economy. The new calculation is called MPGe, and it provides an equivalent of the MPG of gasoline-powered vehicles and those that run on other standard fuels, such as diesel.

Electricity isn’t measured in gallons, of course. It’s measured in consumed kilowatt-hours (kwh). So the estimates that are on the new label rely on a complicated formula that converts electricity into what’s called a gasoline-equivalent gallon. The approach theoretically allows electricity and other nonliquid fuels, such as compressed natural gas, to be compared with a gallon of gasoline. On the new label, the plug-in-hybrid Chevrolet Volt has a combined highway/city MPGe of 93 for electric mode, while the all-electric Nissan Leaf has a combined MPGe of 99.

If the conversion of electricity to gasoline were that simple, MPGe would be at least as reliable a way to predict an electric car’s performance in the real world as MPG is for gasoline-powered vehicles. But because an electric car runs so efficiently, it makes the car much more vulnerable to vagaries, such as driving habits or weather, than a car that’s powered by gasoline, say independent vehicle-research experts.

For example, there’s cold weather. Most car heaters operate on waste heat that comes from the engine, but an electric car must use electric energy that’s drawn from the battery, which can mean that as much energy is going to heat the car as it is to power the car on a cold day. That can mean that it cuts the mileage by at least one-third, says Tom Turrentine, who is director of the Plug-In Hybrid Vehicle Research Center at University of California-Davis.

In addition, most batteries lose efficiency in cold weather, particularly when the temperature drops below about 20 degrees Fahrenheit. That variable also can chip away at MPGe, experts say.

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