When is it permissible to use high beam headlights?

Answer: C — On unlit roads when there are no oncoming vehicles

Using high beam headlights is permissible on unlit roads when there are no oncoming vehicles because high beams provide greater illumination, allowing drivers to see further down the road and enhance visibility in dark conditions. This is particularly important on rural or less populated roadways where street lighting is minimal or absent. In these situations, high beams can help detect potential hazards, such as pedestrians, wildlife, or other obstacles that might not be visible with regular low beams. However, high beams can be blinding to other drivers; therefore, it is crucial to switch to low beams whenever there is oncoming traffic or when following another vehicle closely to ensure everyone's safety on the road. Conditions like foggy weather or lit city roads make using high beams inappropriate as they can create glare and reduce visibility, while using them at any time during the night is not advisable due to these same safety concerns.