What is the name given to the additional feature on the fourth connector allowed by NEMA?

The term associated with the fourth connector as specified by NEMA is the "D connector." This connector serves a specific purpose in traffic signal controllers, often providing a means for additional communication options or enhancing functionality beyond what is provided by the traditional connectors.

In practical applications, the D connector is designed to accommodate various external devices or communication protocols which can be critical for modern traffic management systems that require interoperability with different types of equipment and data management systems. This is especially useful for advanced traffic control measures, monitoring systems, or data collection tools.

Furthermore, the designation of "D connector" aligns with NEMA standards which ensure that systems are compatible and can be upgraded or modified as needed to integrate new technology. Understanding the significance of the D connector helps signal technicians troubleshoot and install traffic signal systems effectively.