I personally think it should be mileage based - the more you drive, the more you pay.
Along those same lines, I'd gladly pay extra for a "high-speed" lane where you have to have a special permit, car and/or license, but basically you are free to drive as fast as you want in it.
2010 E90 335i Black Sapphire
COBB/PTF proTUNE/Alpina/BMS Drop-in/PSS/Blizzak
Best Stock 1/4 time = 14.1 @ 99.4 at Bandimere Speedway (DA = 7,400ft ASL; 13.5 @ 103 corrected)