What is the primary reason for using reflective materials on traffic control devices?

The primary reason for using reflective materials on traffic control devices is to enhance visibility in low light conditions. Reflective materials are designed to bounce back light towards its source, which significantly improves the ability of drivers to see signs and signals during nighttime or in poor weather conditions. This capability is crucial for ensuring safety on the roads, as it helps prevent accidents by allowing drivers to recognize and respond to traffic control devices effectively, even in darkness or low-visibility situations.

While factors like cost, color, and aesthetics may play a role in the design of traffic control devices, they are secondary to the essential need for clear visibility, which is critical for the safety of all road users.