What is the meaning of the following traffic sign?

1. It is forbidden to exceed the speed indicated in the sign (in k.p.h).
2. Correct answer: Road for motor vehicles that are permitted and capable of driving at least the speed indicated in the sign (in k.p.h).
3. Speed limit of 55 k.p.h.
4. It is forbidden to drive slower than the speed indicated in the sign (in k.p.h).

WhyA blue circle with a number is a minimum speed: the road is for vehicles that can and are allowed to go at least that fast. A maximum is not shown this way.