Tax

[Dum-Dum]

The thing is I've seen 45mpg out a V6 mondeo and 20mpg out a prius and I know which is kicking out more emissions so why wouldn't you make the "emissions tax" as it were relative to the amount of emissions a car will actually make because of its usage not because of how economical it could being testing under a very specific set of conditions in a lab that modern cars are made specifically to do well in which is why they have huge holes in fuel maps at certain points in their rev ranges.