It would be far simpler to place a "mass tax" on each vehicle where the heavier vehicle is taxed a higher rate; it would be a simple matter to place scales at gas pumps connected to computers that would adjust the fuel price based on the vehicle weight, a 3,000 pound car would pay the standard gas tax while a 6,000 pound truck would pay twice the base rate, and so on.
Honda Accord: $1.39/gal., Cadillac Escalade: $1.55/gal....
Please don't give them any ideas for a gas surcharge. Just what we need, another way to hit the SUV crowd.
Of course, we could institute a new "Emergency Room and Medical Tax" on smaller vehicles, since their users disproportionately clog hospitals after traffic accidents.