Consumers Confused Over MPG Ratings for Hybrid and Electric Autos

Chrysler’s announcement that prototypes of its soon-to-be-released Volt are achieving fuel economy ratings of 230 mpg under city driving conditions has ignited a firestorm of controversy.

Within days, Japanese automaker, Nissan, posted a “tweet” on the Twitter social media site claiming its new Leaf battery-electric vehicle will achieve a jaw-dropping 367 mpg.

Skeptics were quick to point out that the numbers reported by Chrysler have not been verified by the EPA. The fact that Nissan’s Leaf design doesn’t even include an internal combustion engine (and therefore doesn’t use fossil fuels) drew further scrutiny along with calls for a universal standard for measuring fuel efficiencies for new automotive technologies.

According to many in the automotive engineering community, the new standard needs to employ kilowatt-hour, joules or some other equivalent to the current miles per gallon rating system.

Eric Cahill is the senior director for the Progressive Automotive X Prize Foundation, whose mission is to assist in the development of energy-efficient, affordable vehicles. As automakers continue to produce conventional gas and diesel vehicles and move toward evolving technologies including hybrids and battery-electric vehicles, Cahill says, “We’re now moving from a single-fuel era into a multiple-fuel era.” He says, “Miles-per-gallon just doesn’t stand up anymore, especially when you’re talking about burning multiple fuels.”

GM’s Volt is one such multiple fuel burning vehicles. According to the automaker, the Volt can travel up to 40 miles on battery power before switching to a traditional internal combustion engine. GM, however, has not divulged details on how it arrived at its 230 mpg figure. Senior advisor to the Automotive X Prize Foundation senior advisor John Shore says, “Nobody knows how they made the calculation. They just said they are basing it on what they think the EPA standard is going to be.”

Responding to such criticisms, GM has said that it arrived at the estimate using the EPA draft methodology which the agency has not yet released to the general public. GM also said that the 230 mpg estimated does not take into account electric energy usage. Rob Peterson, a GM spokesman, said, “It’s a pure miles-per-gallon-of-gas figure.”

Nissan said it also employed the EPA methodology in establishing its 367-mpg estimate for the Leaf. According to Scott Vazin, director of product communications for both Nissan and Infinity, the Leaf consumes 0.223 kW-hour / mile. Nissan, he says, calculated the Leaf’s 367 mpg equivalency using the EPA’s 82.049 kW-hour / gallon baseline numbers. Vazin says, “When the vehicle comes out, we believe it will be in the range of 360 mpg.”

Despite clarification from GM and Nissan, many experts insist that current methodologies lack universal standardization and do not provide the transparency necessary to make results usable by consumers.

Cahill contends that automakers are doing their customers a disservice. “Automakers may get some `green-wash’ with consumers by publishing those numbers,” he says, “But as the consumers get confused and skeptical, they will discount those numbers.” The danger for automakers, he says, is that consumers “won’t be able to differentiate one model from the next.”

The Progressive Auto X Prize Foundation is joined by Consumer Reports in its call for automakers to adopt a single miles-per-gallon equivalency (MPGe) standard by which every vehicle can be measured, regardless of its power source. Both contend that the new MPGe measure would be less confusing to consumers than kW-hour, joules or other rating methodologies.

GM underscored the concern over implementation of standards not based on the familiar mpg methodology. Rob Peterson said, “At this stage, we’re building awareness for the Volt and it’s important for us to communicate a metric that people understand. We’re not going to say that the Volt is burning so-many joules to the mile. Nobody would understand that.”

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