This investigation delves into the design principles and ancillary technologies germane to External Human Machine Interaction (EHMI) within the context of autonomous vehicles, with the objective of augmenting traffic safety and efficiency. Fundamental principles encompass the simplification of information, a focus on user centered design, the maintenance of interface consistency, and the preservation of motion continuity. Cutting-edge technologies, including multi-sensor fusion, machine learning, and edge computing, facilitate real-time interaction and precise environmental perception. The research underscores the potential of EHMI to enhance road safety, traffic efficiency, and public acceptance, while also emphasizing the necessity for standardized protocols and adaptive behavior studies to ensure effective implementation.