So what are your ideas on how to tax per kWh?
It's not to tax per kWh.
It's to price it per mile traveled.
Or a fixed fee.
Or a fee depending on where you live.
Or a fee depending on your vehicle axle weights.
Or a function, product or mixture of those.
I don't build roads, so I don't know how we _should_ be paying.
But we have a way of paying for road use via fuel taxation, even though, cost of road use is very obviously not directly linked to fuel consumption. A simple path is to have a system that's the same. Taxation based on fuel consumption is either an efficiency incentive, a proxy or a combination of the two..
If there's incentive efficiency you need to do the same with EVs, so you'd have fees (as in many European countries) adjusted to vehicle efficiency rating.
If it's a proxy, you pay a fee based on the factors for which fuel consumption is a proxy. The obvious factors would be weight and miles driven. By law, vehicles have a VIN and an odometer, so we _already_ have ways of obtaining a value for weight and miles driven. There could be a cost to (double-)checking odometers, but it's not a difficult, or time-consuming task and the sooner countries decide that we need easy access to the VIN and a reliable odometer reading, the sooner it will be legislated as a standard to make it even easier.
Another approach is to get a group of experts on roads to have a good, hard discussion to figure out the ideal pricing system, and then work backwards to a practical system that's as accurate and fair as reasonably possible.
Another approach is to give up, treat roads as a public good, and pay for them from general taxation.
But, politicians are politicians, and sat on their hands during 20 years of technological advances that have made it painfully obvious that the fuel tax system is fundamentally flawed and can't handle those advances, so the politicians are now wringing their hands and treating it as a revenue raising problem, rather than the pricing problem it really is. As a result, they are going for a soft option, because they think, as a Washington state politician openly stated, that EV drivers are affluent, so it doesn't matter if some of them are overcharged by several hundred dollars per year, so it doesn't matter whether a fixed fee is accurate or not.
