What is the rule concerning the use of red lights or flags?

The use of red lights or flags serves a crucial function in transportation and safety regulations. They are specifically designed to indicate that a vehicle is slow-moving or has come to a stop, allowing other drivers to be aware of potential hazards on the road. This is particularly important for vehicles like construction equipment or farm machinery that may not be traveling at the same speed as conventional vehicles.

When drivers see a vehicle with red lights or flags, they immediately understand that they need to approach with caution, maintaining a safe distance and reducing speed. This communication is vital for minimizing the risk of accidents and ensuring the safety of both the vehicle operators and other road users.

The other choices do not accurately capture the purpose of red lights or flags, as they primarily focus on other functions or incorrectly suggest limits to their use. For instance, they are not merely used for decoration or as a signal for help but serve a specific role in conveying the status of a vehicle on the road.