cars are only a certain percent of the total emissions. in fact your usual commuter cars are only 10% of it. everyone could drive a prius tomorrow and emissions would go down 10%. 5-6% is actually the big freight trucks, those would also need to be greened to hell and back.. and then you'd have about 15% of the problem solved.  hence driving eco vehicles is good, it's not like it doesn't do anythign, but it also doesn't do much either. 34% of emissions comes from power plants aka all the coal/gas ones including the countless ones in china. going green/nuclear power would be twice as effective, not to mention evs get their power from the grid which often is using coal/gas anyway so it's more like just outsourcing the pollution back to the power plant and pretending your farts don't stink.
Japan