Final answer:
In foggy conditions, it is safest to increase your following distance to allow for more reaction time and to accommodate for the reduced visibility and increased stopping distances required.
Step-by-step explanation:
In foggy conditions, the correct action to take is to increase your following distance. This is because visibility is significantly reduced, and it takes longer to react to any potential hazards on the road. By increasing your following distance, you give yourself more time to respond to the movements of the car in front of you. A rule of thumb is to follow the four-second rule in foggy conditions, which means you should stay far enough behind the vehicle in front of you that there are at least four seconds between when it passes a certain point and when your car passes the same point.
Maintaining your usual following distance or, worse, decreasing it would be unsafe due to the decreased visibility and increased stopping distances required. Therefore, increasing your following distance is the most prudent course of action in foggy conditions.