Sounds like a great idea, until you think about this:

Unless there is constructed a DIRECT corollary between gas consumption and payroll tax return, or some sort of end-of-year deduction scheme, all this will do is make rich people richer and the poor, poorer.

Low and middle-income people don't go out and buy new cars. They can't afford to. They put $5 in their tanks at a time and go to work. And face it, for the most part, it's the lower-incomers who drive the lower-mileage vehicles.

So these low and middle-incomers see an IMMEDIATE knock to their cash flow but a VERY gradual and probably unbalanced recompense, since the payroll tax 'repayment' would be a national average. And payroll tax is proportional to income, right? So Joe Bubba is laying out hundreds of dollars more in gas costs and seeing only a few dollars return every week. Keep in mind, Joe Bubba is living week to week...

It's only the upper mid and upper income people who will go out and buy that new Explorer with the better mileage. And then see a greater profit, because they're paying the higher tax, but they're getting more back and expending less on gas. The lower brackets will suffer it out and take a beating.

One other possible corollary to make the scheme work would be if there was some sort of subsidization, tax incentive, whatever, to allow lower-income people to go and buy those lower-mileage automobiles.

baa baa, United Sheep of America, it ain't gonna happen, there's too much stroke and too little incentive, especially culturally, against conservation. Ask yourselves why don't we have more mass transportation, for instance?