What vehicles may enter a cycle highway that has this sign?

This sign indicates a "Fahrradstraße" (cycle street) where primarily bicycles have priority and the road is designed mainly for them. The additional sign "Anlieger frei" means that residents or people with legitimate business in the area (residents or local traffic) are allowed to enter with their vehicles.

According to German traffic rules, only residents and local traffic ("Anlieger") are permitted to enter motor vehicles in this cycle street. Other motor vehicles are generally prohibited to ensure safety and priority for cyclists.

The other answer options are incorrect because:

- Mopeds with a maximum design speed under 25 km/h are generally not allowed on a Fahrradstraße unless they are driven by residents or local traffic.
- Cars are not allowed to enter, even at walking speed, unless they belong to residents or local access traffic.

So, the rule is that apart from bicycles, only vehicles driven by residents or local traffic may enter this cycle highway, in accordance with the "Anlieger frei" sign. This maintains the cycle street's primary use for cyclists and limits through traffic.