A common misconception. Friction losses from airflow cube with any increase in velocity. So as an example if you reduce velocity by 20% friction from airflow reduces by 50% and therefore energy needed to overcome it reduces by 50%. So despite being in the area for longer, the amount of fuel and therefore emissions are reduced.In Newport on the M4 there is an area where it goes down to 50 because the signs say kill speed air pollution kills.....Now, I don't know a lot about this stuff but surely if you are doing 70 you get through this area quicker so less pollution.....Or if you go 50 you are in the area for longer so more pollution. Now if there is more pollution at 70 then surely the fact you are in the area for longer at 50 it cancels it all out and 70 is no different to 50 ?
Put it this way, if the fuel light is on in your car and you are worried you won’t make it to the petrol station, do you drive there more quickly, or more slowly?