Tom
If I understand you correctly, less cars=less petrol consumption=less carbon emissions. That appears to be the goal. Here are a few other ways to do this:
1 Increasing MPG standards to 25mpg would reduce U.S. oil import dependency by 20%. Taxes required.
2 The free market has an answer - the hybrid car. You gain 25% better mpg vs. gasoline car. No taxes required.
3 Diesel cars get 30% better MPG, last longer, cheaper to buy.
4 Diesel-hybrid cars gain 30% more MPG by diesel, and 25% more mpg with an electric hybrid, creating a 55% more fuel efficient car.
5 Biodiesel-hybrid cars. 55% more MPG, and less carbon emmissions. Now we're talking!
Combination=Solution. None of these alone will solve the problem. A combination of 1-6 together will help solve petrol import, environmental, economic problems.
Thanks for weighing in here and sharing ideas.
Will Thurmond
Author, Biodiesel 2020
http://www.emerging-markets.com/biodiesel