While we are on the subject of "green" stuff, the Americans have named fuel saving driving measures "hypermiling". Bit of a daft name, and common sense to some. It is possible in any car and comes as instinctive. You can only do it within the limits of the car you have, so the more modern it is the better. I don't know when manufacturers figures for fuel consumption are supposed to change, but the old system (urban, extra urban, average) is nonsense and unachievable, at least in small cars. I had a Suzuki Alto 3 cylinder 1 litre petrol engined car for a bit, it was supposed to do over 60 mpg, but the best I ever got (with some hypermiling techniques) was 55. Mainly it is what you do with your right foot, whether it is diesel (spit) or petrol or some hybrid thing. It would also work in an electric car. Efficiency is the thing. I won't say what you have to do, that should be common sense, but there are websites which describe the techniques. If more people drove in this way fuel useage, and hence emissions would decrease.