When I say gradually, it's an euphemism, it's an _extremely_ slow process, but it's the global tendency here.
generally what's happening is a combination of:
* making pedestrian zones (i.e. banning)
* deny access to certain types / times (no vans, no old cars, etc.. i.e. also banning)
* reducing roads (i.e. 2 > 1 lane, thus reducing attractivity)
* raising driving prices (the congestion / air quality certificates you mention)
* reducing access to parking (remove places, make them more expensive, etc)