What is the primary risk of driving in fog?

The primary risk of driving in fog is reduced visibility. Fog can significantly impair a driver's ability to see the road, other vehicles, and any obstacles that may be present. When visibility is limited, it becomes challenging to judge distances and speeds accurately, which can lead to dangerous situations such as collisions or losing control of the vehicle.

In foggy conditions, it is crucial for drivers to adjust their speed and maintain a safe following distance, as they may not be able to see brake lights or other indicators until it is too late. Additionally, using high beam headlights in fog can create glare and further reduce visibility, making it even more essential for drivers to be cautious and aware of their surroundings. Ensuring proper use of low beam headlights and fog lights can help improve visibility in these conditions but will not eliminate the inherent risks associated with driving in fog.

The other options, while they may be concerns in certain circumstances, do not represent the most immediate and critical hazard presented by foggy driving conditions.