Under the NRTA, when is a driver permitted to drive on the left shoulder (yellow lane) of a single-lane road to allow another vehicle to pass?

1. At any time, provided the passing vehicle is flashing its lights.
2. During daytime, on a flat road with clear visibility for at least 150 meters, and only when it can be done safely without endangering pedestrians or other traffic.
3. Only during night-time, to maximize safety.
4. It is strictly illegal under all circumstances.