A mileage tax is a tax levied for road usage. It would be the closest thing we have to a tax that actually charges users for the wear-and-tear on roads they are directly responsible for. The major problem with this kind of scheme is administrative expenses. Which is why an unfair flat tax regardless of mileage on electric vehicles is likely to be the "solution".
Actually we already are taxed on our use of the roads via gasoline taxes... which are pretty much exorbitant and never are used to repair roads. Mileage taxes begin to invade privacy by collecting individual data... erodes liberty. Not a conservative solution at all. Again.. Wow... I hope you are kidding.