What action should be taken if an oncoming vehicle does not have its headlights on during low visibility?

Using the horn to alert the driver while proceeding with caution is the appropriate action when encountering an oncoming vehicle without its headlights on in low visibility conditions. This approach serves two purposes: it helps to notify the other driver of their potentially unsafe condition, and it emphasizes the importance of caution due to the reduced visibility that both drivers are experiencing.

In such scenarios, maintaining a safe distance and being vigilant is crucial. Flashing headlights can also alert drivers but might cause confusion or result in a misinterpretation of intent. Speeding up to pass the vehicle quickly is dangerous as it could lead to a loss of control or increase the risk of a collision. Turning around to find an alternate route may not be practical or safe, especially if it could lead to longer exposure to risky driving conditions. Therefore, using the horn for alertness while remaining cautious is the most balanced and sensible course of action.