What a load of witless drivel. A car WONT DO 20 mph in fourth or fifth gear. So in 3rd gear at 20mph you will be emitting the same CO2 and particulates as a car doing 30 mph in fourth. You will be in the zone for 50% longer emitting 50% MORE CO2 for the journey. The 20 mph zones are asinine, all they do is annoy people. Is there anyone on here that lives in the real world?