New MPG

I just read this quick write up about how the Chevy Volt, which is to be released next year, will have a MPG rating of 230. That's a lot. But that's also the point. I don;t mean to belittle the achievement. I do mean to attract attention to the problem here. I think MPG is only a good measurement of fuel economy with traditional liquid fuels. By branching off and making the volt primarily electrically powered, the Volt uses very little gas, but it does use energy and fuel to move. I think we need an across the board measurement of economy. My first instinct is to measure miles against CO2 output. That would give an industry standard to measure across all types of vehicles: hybrids, gas, diesel, electric, hydrogen, etc. That way you can measure the carbon output and compare. Yes, MPG is useful in figuring fuel costs, but the environmental advantages need a new metric.