Where:
On any road where the roadway ahead becomes very narrow,for example, at a bridge, tunnel, culvert, or passage, allowing only one vehicle at a time to pass safely.

Purpose:
To warn drivers in advance that the section of road or structure ahead is too narrow for two vehicles to pass side by side.
This ensures that drivers approach cautiously and prepare to give way to oncoming traffic if necessary.

Action:
Reduce your speed as you approach the structure.
If you see an oncoming vehicle already entering or close to the narrow section, stop at least 6 metres before the structure and yield to allow that vehicle to pass through first.
Proceed only when the way is clear.
Always be patient, make sure your vehicle can fit safely, and be alert for pedestrians, cyclists, or animals that may also be using the narrow passage.