Final answer:
Driving speed in fog is highly dependent on visibility, road conditions, and weather conditions; often requiring driving below the posted speed limits to ensure safety.
Step-by-step explanation:
How fast you drive in fog is mostly dependent on a combination of several factors, with visibility being one of the most critical. In conditions of poor visibility, such as heavy fog, it is imperative to reduce your speed to ensure that you have adequate time to react to any obstacles that may appear on the road suddenly. Road conditions are also crucial to consider, as they can be affected by weather and can lead to increased hazards during foggy conditions. While speed limits do set the maximum lawful speed, in many cases, it will be necessary to drive below these limits in fog to maintain safety. Weather conditions themselves directly influence visibility and road conditions, making them integral to determining safe driving speeds in fog.