Can't tax mileage without privacy invasion and tedious paperwork, and unfairness in general.
Just tax tyres. One rule for everyone, works a treat. Massive incentive for manufacturers to make tyres that last longer too.
Cas 
Actually they can and it's quite easy.
Each year when you go in to renew your plate / registration. ask, whats the odometer read? There's what they need, fine, you drove 13k miles / km at 3.2 cents a mile so you owe us xxx for the tag.
if people want to get childish about it then charge them a flat rate of 500 dollars. Your insurance company collects this data when they renew your policy. How much do you drive so we can adjust our rates for YOU accordingly.
I don't care where you drove or went, what time, how many times, bla bla, just how many miles last year did you drive?
if you own a business and are writing off miles / vehicle use you darn sure bet you the IRS wants to know this info too !
in fact, they should just do this for EVERYONE. Gas / electric, it don't matter, you pay by use. For those who own fleets of vehicles because of the nature of their business, then that price gets baked into the cost of what they charge. It really IS fairly easy to do if we could only get a few adults to the table to figure it out

Aaron