It all depends where the councils put their monitoring equipment, for instance one of the Kirklees Council's stations overlooks the M62 on an overbridge a few hundred yards from my home and hence the local school is also heavily polluted. But Kirklees has a large area and such separate town centres HUddersfield, Dewsbury, Batley and Cleckheaton, I'm not sure how one determines what measures should be put where.
There again I have read the suggestion that the Tinsley Viaduct in Sheffield which carries the M1 over the valley will need to have a reduced speed limit to reduce the pollution in the valley but there again those of us that can remember steel making in Sheffield and the level of the visible pollution that used to hang over the city and that valley, wonders what all the fuss is about.
But on another point its about time that vehicles that spend their life in the city centres are cleaned up first, buses, taxis, private hire cars, rubbish wagons etc
alan