Final answer:
Driving slower than the posted speed limit is necessary in bad weather and heavy traffic for safety reasons.
Step-by-step explanation:
Driving slower than the posted speed limit is necessary in specific situations for safety reasons. In bad weather conditions, such as rain or snow, it is important to reduce speed to maintain control of the vehicle and prevent accidents. Heavy traffic also requires driving at a slower speed to ensure there is enough time and space to react to changing situations on the road.