I've written about this before, but just to restate my objections...
The gas tax is already an approximation of a mileage tax. To the extent that it isn't a perfect mileage tax... great! It's also tax on heavy cars, which cause more road damage, and a tax on gas guzzlers, which are, you know, bad.
As for the politics... I don't get why people think that "well, it's politically infeasible to raise the gas tax, but voters will just love it if we set up a costly system to track all of their driving habits and send them a bill for how much they've driven." Just weird.
