What motor vehicles may enter an environment zone that has this sign?

This sign indicates an environmental zone ("Umweltzone") in Germany, where only certain vehicles are allowed to enter to reduce pollution. The main rule is that motor vehicles must have a green particulate emissions sticker to enter this zone legally. This sticker proves that the vehicle meets strict emissions standards.

Motorcycles are also allowed to enter the zone regardless of having a sticker because they generally produce less particulate matter.

Vehicles that meet the emissions requirements but do not display the green sticker are not allowed to enter. The sticker must be visibly attached to the windshield.

So, to summarize:

- Motor vehicles with the green sticker can enter.
- Motorcycles can enter even without the sticker.
- Vehicles without the sticker, even if they meet the emissions standards, cannot enter.

Understanding this rule helps protect air quality in certain urban areas by restricting higher-polluting vehicles.