How much you want to bet all the car manufactures fall way short of this and simply negotiate a reduction so its hardly meaningful?

People want their cake with no pain. If you want high mileage cars, and to reduce emissions etc, you need to raise the price of gas. As we saw last summer the breaking point is $4-$5 a gallon. The goverment can do this with taxes, and while it would be painful short term, long term it would probably be better.

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1999 SL500
1969 280SE
2023 Ram 1500
2007 Tiara 3200