Gas mileage and driving

I keep hearing on CNBC and reading at some blogs that if cars get better mileage that people will drive more by enough to offset the improved mileage.

I can see that people could drive more because of the savings. But to argue that reducing mileage by 20%, for example will lead to people increasing their driving by more then 20% seems like a very questionable conclusion. I’m willing to listen to an argument that increasing gas mileage would be partially offset by increased driving, but not that the responses would be more than 100%.

Does anyone have any idea of the original source or research of this belief by so many Republicans, Conservatives and Libertarians?

Is it just another Wall Street Journal editorial page finding that is too good to be true?