Under what conditions should you apply the four-second rule?

Answer: B — If the road is wet or frosty

The four-second rule is a guideline that helps riders maintain a safe following distance under various driving conditions. This rule becomes particularly important when the road is wet or frosty because these conditions can significantly increase the stopping distance due to reduced traction. When the road surface is slippery, such as in wet or frosty weather, motorcycle riders should allow for more distance between themselves and the vehicle in front to give themselves ample time and space to react in the event of sudden stops. Maintaining a greater following distance, like the four-second rule suggests, allows for a safer riding experience by providing a buffer that can accommodate the longer stopping distances caused by decreased tire grip. Consequently, this rule is critical for safety and accident prevention when weather conditions are less than ideal.