Oh I wasn't directly trying to fight/contradict Marti. Just stating some facts on how things are actually done, including reading more about it myself, as I am no car pollution expert. Although I deal a lot with emissions in my industry. When you change spare parts on much larger machines then car engines you have to note all the information of where they come from down, and make sure they're approved, as this effects your NOx out puts.
There is a lot of independent miles per gallon tests in the UK, I know this. You can buy a lot of independent magazines every month with lists of new or second hand cars and their pros and cons, and the independent MPG is normally in there.
There is different MPG readings given for urban and normal driving. But if the engine is idle, and the car is not moving, I think this is what you mean, then the idle consumption is very roughly realitive to how many litres the engine is, so a 1.1 litre city car will spill a lot less exhaust when the car is not moving, then a 6 litre Pick up truck. Because the larger litre engines always have more energy loss, due to larger or more cylinders, and more mass of moving parts in engine causing more resistances.
http://www.consumerenergycenter.org/tra ... osses.html
The losses of aerodynamic drag, rolling resistance, intertia are pertically larger on larger vehicles, but really all of the things noted on the above link are larger on larger engine, larger SUV/pick up trucks.
As stated before, some modern engines turn off in idle, and on again as you proceed to move. This also occurs in fully electric cars, electric cars also have a lot less resistance, as they have a lot less components. They are also a lot less likely to break down, because they are a lot less complicated. Not only did the oil industry block electric cars for a long time, but car manufacturers were scared as they make a fortune from spare parts.
If you have not seen the Documentary, Who Killed the Electric Car, I highly recommend it, really well made and interesting documentary, as well as being related to this topic, but in the smog of Califonia instead.