Maybe Nissan and GM are still talking in MPG because that’s all they know, but the EPA and NHTSA are also partly to blame for the confusion.  The first problem is that consumers are accustomed to gauging efficiency in MPG, so the big auto makers and the EPA are inclined to rate fuel economy of electric vehicles using a MPG equivalency figure.  The second problem is that since car companies must comply with strict Corporate Average Fuel Economy (CAFE) regulations set forth by NHTSA, electric vehicles must also have some sort of MPG value applied to them for the purposes of calculating regulatory compliance.  Consequently, the resulting calculations and policies have more to do with politics and influence that any basis in science.

In fact, under the current CAFE rules, the MPG equivalency of an electric car is calculated assuming about ~82kWh of energy per gallon of gas, when the actual energy content of a gallon of gasoline is about 34kWh. Meaning, the CAFE regulations have essentially changed the law of physics to artificially enhance MPG for electric cars, and all to give manufacturers a boost to comply with the regulations.

We get that fuel economy is one of the biggest factors when people buy a new car. It’s such a big deal that according to a Pike Research study, 85% of respondents said that improved fuel efficiency will be an important factor in their next vehicle purchase. But, we also think that MPG equivalency ratings aren’t an honest way to communicate electric car fuel economy to consumers.   To us, it’s like comparing apples to oranges.

The efficiency of an electric vehicle has nothing to do with gallons of gasoline, so why are we still talking in miles per gallon?  Using the EPA’s approach for the Chevy Volt fuel efficiency rating, the CODA electric car would have iMPG – infinite miles per gallon – because it doesn’t use ANY gallons of gasoline.  So while EPA fuel economy ratings can give consumers a way to compare the efficiency of one vehicle to another, when the calculations are driven by politics and influence rather than hard science MPG equivalencies only confuse consumers more.

At CODA, we believe the best way to measure efficiency of an all-electric vehicle is by calculating the amount of energy used per mile (watt hours per mile.) This also gives consumers an accurate way to compare different electric vehicles side by side.  We think the issue is confusing enough and that we shouldn’t be trying to compare electric cars to internal combustion cars when it is obvious that they are completely different.

As for plug-in vehicles that have some amount of “all-electric range” but also use an internal combustion engine either in parallel (Toyota Prius) or in serial (Chevy Volt or Fisker Karma), a new approach is needed. Plug-in hybrid vehicles should be rated on “electricity per mile” for the all-electric component and traditional MPG for when the engine is running. Both ratings should be shown on fuel-economy stickers.

Now that’s more like apples to apples.