Building a car is estimated to consume 1764 gallons of oil (42 barrels).
If you buy a new car every three years and drove 30,000 miles total, you would have already used .0588 gallons oil per mile just to build it. Taken alone, that's 17 mpg even if you car is so efficient it burns no gasoline at all.
What does this mean?
Idle or prematurely retired cars are a waste of oil. Parking one's late model SUV and getting a Prius definitely isn't the greenest thing one can do.
To be really green, consider buying only used cars instead of new ones.
The government should consider offering incentives for establishing a vibrant, job-creating used-car-rebuilding industry.