I live in Oregon, one of the states proposing a per mile tax on EV's. One of the authors of the proposed tax had this to say about it a couple days ago on a radio talk show. First, any tax would exclude EV purchased or in existence before 2014. This exclusion is for the life of the vehicle. (So hurry up and buy your Tesla, those on the fence). This exclusion is to incentivize people to buy EV's. The second part is that they want it to be calculated on miles driven. They don't want a flat tax, like our neighbor Washington state is proposing.
To editorialize, I have no problem paying my fair share for "road use", but I think it should be miles driven and weight of the car, as we know the heavier the car the more road wear. Second, how we report miles driven is a little problematic. Do we rely on people's honesty and submit a form with a declaration of miles driven. Maybe submit of photo of the odometer to show the miles driven in a year. Or do we put some layer of inspection, like we have to bring the vehicle to DMV to have the odometer inspected to verify the number of miles driven.
In Oregon, we have to take our ICE cars to be checked by Dept of Environmental Quality every two years, maybe this would be acceptable, where we take our EV's in every two years for an odometer inspection.