That’s a terrible metric. You want to deter vehicles that use a lot of fuel disproportionately to the cargo they’re carrying — not just punish heavy vehicles.

Most automobiles in the US are designed to carry up to five people, and almost always carry just a single person.

It still makes sense to target those with an MPG requirement.

We could also eliminate the Federal tax credits for farm vehicles -- actually we should alter the vehicles which qualify for the subsidy. Because current tax law encourages the purchase of vehicles larger than 8000 pounds for primarily personal, non-farm activity.

Almost insane touch that one, though; it hands the story to those who would oppose any reduction of carbon subsidy. I mention it by way of illustrating one of the myriad ways that hardworking, independent Americans depend upon Federal handouts. (Using emotionally provocative language on purpose here. I prefer to avoid such framing, not useful. Here I use it by way of another illustration of warped perspective on carbon economy status quo.)

What SUVs are carrying enough cargo to justify their mpg? I think commercial transport is of scope of what the commenter meant rather than the swath of empty pickups and jeeps being driven as daily drivers.

The only way to make people care about fuel economy is if it hits them in the pocketbook, like a few years ago when gas was above $4/gallon.

Unfortunately gas taxes to force the price that high under current circumstances are terribly regressive and politically suicidal in all but the most secure jurisdictions.