Without knowing the general driving population's driving habits, it's difficult to estimate how effective driving will improve fuel efficiency and/or reduce pollution. Sure there are known bad driving habits like sudden accerlation/sudden stops will increase fuel consumption, but what about road sign design, speed limits, traffic light designs and Electronic Toll Collection systems? Those are all factors of fuel efficiency.

Also, the government regulation on emission is going to get tighter and tighter due to incentives to push for EV adoption. So arguing emission test method is a moot point.