With all the chatter about the need for stable funding for municiplaities, American states are also finding out that their traditional sources of revenue, like the gas tax, are not that stable. The problem with the state is that its left hand never knows what its right hand does. So when the state taxes gasoline to raise revenue (don't think it was to discourage driving), but also insists on better mileage for cars, it seems logical that better mileage means less consumption of gasoline. This means less revenue, which means the state needs to find different ways to raise money.
In the old days, kings used to get innovative. They taxed based on the size of one's windows. They taxed tea! Today, they want to tax drivers based on mileage. Of course, user pay is the issue. Heavy car users should pay more for roads than lighter automibile users. Of course, this is foolproof, because human innovation never figures out how to outwit the state. And of course, privatization of the roads never occurs to the politicos, because that would diminsh their reason for existing in the first place.