The fallacy is assuming that the fuel economy of standard cars can be raised from 30 to 60 mpg.
It would seem reasonable to assume that the marginal benefit of diminishing fuel economy will be achieved by marginal vehicle ownership costs that rise at a steeper rate.
There is no calculation for the carbon emission associated with the marginal vehicle ownership rise
I don’t want to see a 40 mpg light truck pull a 16,000 pound trailer or even a 7,000 pound one. I don’t even want to see a 40 mpg light truck.