But road usage by cars is not the problem, CO2 emissions is. By doing this kind of punishment-by-proxy the whole taxation becomes ideological (car too big, car too foreign) and loses legitimacy. Keep in mind that in a democracy you shouldn't aspire to force people to do "the right thing", you should aspire to create consensus. A high tax on gasoline is easy to understand and easy to argue for. Double payments, illogical taxation, and "nudging" just pisses people of into the arms of right-wing parties.