Researchers Proposing Method for Determining Plug-in Mileage
 

http://ecogeek.org/images/stories/prius-dyno.jpgThe Society of Automotive Engineers and the National Renewable Energy Laboratory are recommending that the EPA come up with two different ratings for plug-in vehicles: miles per gallon and electricity per mile.

The two groups will finalize their proposal within the next six months, hoping to prevent the EPA from coming up with a rating that combines gas and electricity mileage like the sky-high MPG claims GM and NIssan recently came up with for their plug-in models. Jeff Gonder, an NREL researcher says "If you combine them into one (number) artificially, you can't derive a final output like annual costs."

If fuel efficiency is stated in terms like electricity per mile and gallons per mile, the cost of fuel in both forms is immediately apparent to the consumer
NREL is also coming up with a new way to judge fuel efficiency with dynamometers. Instead of just putting the car on the machine and seeing how far it can go until the tank is empty, a procedure that doesn't reflect actual performance for plug-ins, the researchers are mimicing average driving behavior on the machines to come up with average yearly fuel costs.

So, is it MPG or GPM?

2 mpg is .5gpm. Why not just say watts or kilowatt per mile?

I prefer CO2/mi.

depending on the power source the CO2/mile could well be 0 but would still have a real cost in terms of the cost of energy.