Here in North Carolina, gasoline taxes fund roads and public transportation. Cutting taxes, as this story from 2006 describes, directly impacts that infrastructure.
As high oil and gas prices today reduce demand, revenue to maintain that infrastructure decreases.
In a future where personal vehicles don't run on fossil fuels, where will that money come from? The general fund? Bonds? Taxes on electricity and natural gas? Tolls?
My futuristic guess: In the future, you will subscribe to American Super Highways(tm) road service, just like you subscribe to Internet service, thus giving your vehicle or PRT access to that roadway.
In any case, if gasoline-fuelled cars become the minority, that "hidden" cost must be borne elsewhere. This is not a criticism of any particular policy. I'm merely a technocrat wondering aloud about an unsolved problem we must eventually confront.