(I know, this is really radical...but...)
How about creating incentives for people to drive lower-emitting cars? How, you ask? Try this...currently, the cost of registering your car is based on the value of the car. Instead of that, base the cost of registration on the grams/mile of emissions produced by the car (and the year-over-year odometer reading). A model T might cost you $10,000 per year to register, while an EV-1 might cost you $250-$500 per year.
Keep in mind that there is no such thing as zero emission automotive transportation. Even an electric car requires emissions at the point of electricity generation.
So, we'd have to save that $0 registration fee for some yet-to-be invented solar or wind-powered car.
Is there any transportation at all which is "zero" emission? Nuclear submarines, I guess...until you have to decommission. Or maybe bicycles--except for the CO2 exhaled.
--Boris