A good point brought up here, is that if you tax on a yearly basis much like your income tax. People will find good ways to avoid it, like the miles are included in their business travel so they include it with their deduction etc.....
If you charge a new car road usage tax, you can't avoid or fraud it. The dealership collects the money and sends it to the government bank account along with their sales tax. Everything is charge at one time, far less administration and headache for drivers. The tax is rolled into the car loan so it's alot easier to pay for spread out over 12 monthly payments for 5-6 years. The added bonus to the goverment is less controversy and backlash. Paying another yearly tax will rile the people up every time they have to calculate their mileage and write out a fat check.