Which type of device is placed by a public body to regulate, warn, or guide traffic?

The term "official traffic control device" encompasses all devices placed by a public agency to regulate, warn, or guide traffic on roadways. These devices include traffic signals, signs, and pavement markings that help manage vehicle and pedestrian movement, ensuring safety and efficiency in traffic flow. The classification as "official" indicates that these devices are authorized and standardized according to government regulations, which helps drivers and pedestrians follow consistent rules on the road.

While traffic lights, private warning signs, and directional markers may serve specific functions, they do not cover the full scope of what an official traffic control device represents. Traffic lights are a subset of traffic control devices but do not include all forms of regulation or guidance. Private warning signs are not issued by public authorities, and therefore, do not qualify as official devices. Directional markers also provide guidance but do not encompass the regulatory and warning aspects critical to traffic management. By recognizing the comprehensive nature of official traffic control devices, it is clear that this option is the correct choice for the question regarding how traffic is managed by public bodies.