[tspiteri]

I'm finding it a bit hard to make sense of your comment.

I don't know of that "many vehicles that will do far over 55mpg on a fossil fuel powered engine."

And how is "higher mpg = higher carbon emissions"? Higher mpg means less gas per mile, leading to less emissions per mile. As for the claim that government "can easily control maximum mpg", really?

So either I'm not seeing it properly, or the comment is anything but "simple logic".

[Someone]

Slight nitpick: higher MPG does not necessarily mean less emissions per mile; car engines do differ in the amount of emissions they produce per gallon of gas consumed.

For example, adding a catalytic converter to a car may decrease both MPG and emissions (http://en.wikipedia.org/wiki/Catalytic_converter#Environment...), so removing it may increase both MPG and emissions. And that is even disregarding the fact that adding that converter increases the weight of the car.

[zurn]

Also the fuel has a large impact on the MPG since fuels differ in energy content per volume.