What type of unit controls the traffic signal controllers in today's traffic systems?

The microprocessor is the correct choice as it represents the advanced technology utilized in modern traffic signal controllers. Microprocessors are integral components that perform calculations, process data, and execute control algorithms essential for managing traffic lights efficiently. This technology allows for adaptive signal control, where the traffic signals can adjust in real-time based on traffic flow, improving overall traffic management and reducing congestion.

Microprocessors also facilitate communication with other devices and systems, enabling the integration of traffic signal controllers with traffic management centers, cameras, and sensors. This capability enhances the coordination between signals and various traffic control measures, ensuring safety and efficiency on the roads.

In contrast, other options like electro-mechanical devices, analog switches, and relay systems represent older or less sophisticated technologies. These systems lack the flexibility, programmability, and real-time processing capabilities found in microprocessor-based controllers, making them less effective in meeting the demands of today’s traffic environments. Thus, the adoption of microprocessor technology is a significant advancement in traffic signal control systems.