What is the meaning of a circular sign with a red border containing the text '4.4m' with black arrows pointing to it from the top and bottom?

1. The minimum distance between two vehicles is 4.4 meters
2. A height limit of 4.4 meters; vehicles taller than this cannot pass
3. The road width is 4.4 meters
4. The distance to the next highway exit is 4.4 km