What tax is this proposed tax replacing?
When we all drive electric or homebrew biodiesel cars, there will be no gas tax to pay for roads.
And as fuel economy increases from better engine design and lighter/smaller cars, existing gasoline tax revenue drops. The gasoline tax model is simply not sustainable. Most states already require cars to come in for emissions checkups every other year. Why not require electric cars to come in for a mileage check and tax accordingly? Isn't this the model for public utilities? Some municipalities have automated utility meters that send real-time usage data back to HQ. If folks are OK with that, why not mileage tracking on cars? (BTW your cellphone company, and probably the goverment already knows where you go if you leave your cellphone on all the time. Who needs GPS lol!)
Another option is to make a default use tax for each vehicle and offer rebates the less you drive. You purchase the right to drive up to 15,000 miles via monthly fees, but get a big rebate at the end of the year when you only drive 10,000 miles. Insurance companies are already doing this, so why not the government? You can even have special provisions for low-income households who have to drive a long way to work and are underserviced by public transit.
But these are just ideas. Ideas are bullshit. Execution is what matters, and thats fucking hard to do.