Cars will have to include a mandatory windshield sticker stating their pollution levels, according to the Euro xx standards and will be subject of fines if the most polluting ones get to the city center. This is specially important for diesel cars: most of them don't have DPF installed. DPFs can actually improve the color of the car's sticker. Red color will be for cars that produce more than 50 mg of particules per cubic meter of air (Euro I).
The banned areas are established by every municipality. Drivers caught will have to pay a 40 EUR fine and lose one point from their driver's license. German authorities are helping motorists retrofit their diesels with DPFs through a 330 EUR subvention.