[ubqbuppp] Car fuel economy

Why is it that in America we set fuel economy standards for manufacturer fleets to reduce carbon emissions instead of simply raising a gasoline tax and letting the market develop fuel-efficient cars?

Raising the gasoline tax could be coupled with lowering the income tax to make it revenue-neutral for the government and politically palatable.

Is the problem that when a consumer chooses a car to buy he or she cannot easily see the fuel cost and consequently acts irrationally? The nanny state is trying to correct a flaw in human nature and induce rational behavior? Not that this is wrong.