What does a circular traffic sign with a red border, white background, black digits, and two vertical inward-pointing triangles (e.g., '3.5m') indicate?

1. Restriction on Clearance Height: prohibits vehicles with a total loaded height exceeding 3.5 meters from entering
2. Restriction on Clearance Width: prohibits vehicles wider than 3.5 meters from passing
3. Safe Following Distance: mandates a minimum gap of 3.5 meters between trucks
4. Elevation Marker: indicates the roadway is 3.5 meters above sea level