Where:
This sign is displayed at the beginning of a single-carriageway freeway, where the road changes from an ordinary public road into a controlled-access freeway that carries traffic in both directions without a central dividing barrier.
These freeways are usually found in rural or semi-urban areas, where traffic volumes are lower and physical separation between lanes is not always necessary.

Purpose:
The purpose of this sign is to inform drivers that a single-carriageway freeway begins at this point, and that all rules, restrictions, and driving regulations that apply to freeways come into effect from this location.

This helps to,
    Alert drivers to the transition from an ordinary road to a freeway,
    Ensure compliance with freeway regulations such as access control and speed limits,
    Promote safe driving behaviour in an environment with higher-speed traffic and limited stopping points, and
    Improve traffic flow and safety by standardising driver expectations and actions.

Action:
From this point onward, follow all freeway rules, including,
    No stopping or parking on the carriageway or shoulder except in emergencies,
    No pedestrians, cyclists, or animal-drawn vehicles allowed on the freeway,
    Enter and exit only at designated on-ramps and off-ramps,
    Observe the speed limit applicable to freeways,
    Keep left, pass right, and maintain safe following distances.

Exercise extra caution when overtaking, as traffic from the opposite direction travels on the same carriageway without a median barrier.