If you walk through the center of a German city, you will rarely smell one thing: car exhaust fumes. Environmental zones have been established to improve air quality. This means high-polluting vehicles are prohibited in city centers.

Colored stickers prominently displayed on the windshield provide information about a vehicle's emissions. The environmental friendliness increases from no sticker (very harmful) to red and yellow to green. The appropriate sticker, for example, can be obtained in car repair shops for as little as €5. The majority of environmental zones are off-limits to vehicles without a sticker or with a red sticker, which are mainly older diesel vehicles. Berlin, Hanover and nearly 50 other cities have stringent regulations: Only vehicles with a green sticker are permitted in the low-emission zone. Each year, more and more cities implement these regulations. Anyone caught driving in such a zone without the appropriate sticker faces a €40 fine as well as a penalty point on the German traffic offenders' index.

What if your sticker doesn't pass muster? Then you have to park your car outside of town and take a bus or train to the city center. One ray of hope for these car owners: cities' well-developed public transportation networks!