Which of the following conditions makes it permissible to drive more slowly than the minimum speed?

Driving more slowly than the minimum speed is permissible under certain conditions, particularly when safety is a priority. Heavy traffic situations can necessitate slower driving as vehicles may be closely packed together, making it unsafe to travel at higher speeds. In such cases, the flow of traffic and the ability to maintain a safe distance between vehicles become more crucial, allowing drivers to go below minimum speed limits to ensure everyone's safety.

Weather conditions also play a significant role in this scenario. Adverse weather, such as rain, snow, fog, or ice, can severely impact visibility and road traction, compelling drivers to reduce speed. This adjustment is important not only for personal safety but also for the safety of other road users. In poor weather, going slower than the minimum speed may be the best decision to navigate safely through challenging conditions.

Together, heavy traffic and adverse weather conditions justify the need for slower driving than the established minimum speed limits, making both conditions relevant to the answer.