Here in Germany, if you have a car without Euro 3 or better, you can't drive into towns at all. You have to stop outside and use park and ride.
You have to get a windscreen sticker from the TÜV (MOT), which is colour coded. If you car doesn't qualify for one of the Euro norms, you can't enter the town, if you car does qualify, but you haven't bothered to get the sticker, you can't enter the town.
I had a particle filter put on my Mondeo, so I get a 4 sticker, instead of 3, so my tax is also cheaper.