Some Money With Your CAFE
I'm with Beutler and DeLong that raising CAFE standards would be better than not raising CAFE standards because it would be better to have higher gas taxes, and then not having higher gas taxes either because it's too unpopular, but I don't think CAFE fans should go as far as Brian does in obscuring CAFE's limits as a policy option. It's true that driving habits aren't incredibly responsive to short-term changes in the price of gas, but they're not completely inelastic and their may well be more long-term sensitivity.
CAFE, meanwhile, relies entirely on the fuel efficiency lever as a means of reducing gasoline consumption even though the total amount of driving is clearly an important determinant of how much gas gets used.
Most of all, though, gasoline taxes, apart from their impact on carbon emissions (and emissions of other things), raise revenue which is useful in a number of ways. I feel like something green types tend to overlook when citing political feasibility as the reason for preferring certain kinds of regulatory measures to tax-oriented ones is that from the point of view of progressive politics more broadly the politically difficult task of raising taxes just can't be postponed forever. Raising the gasoline tax would be politically difficult. But so would instituting a VAT. And so would an across the board income tax rate increase. And so would everything else. Just getting the Bush tax cuts to expire will be a non-trivially difficult task, but implementing progressive priorities on health care, education, etc. will require even more revenue than their cancellation would raise.
It seems to me that there's a case to be made for going bigger -- for taking on a task that, while more politically difficult, also helps a broader coalition of people accomplish their goals.
(NB: needless to say, higher gas taxes and tighter CAFE standards aren't mutually exclusive policy options)