## 5 Discussion  
This study effectively categorized perceived anthropomorphism into three levels, corresponding to Agents A, B, and C. The results indicate a clear and significant increase in perceived anthropomorphism from Agent A (machine voice and no humanized speech strategy) to Agent B (human voice and no humanized speech strategy), and from Agent B to Agent C (human voice and humanized speech strategy). This progression confirms that the agents were designed in such a way that the incorporation of human-like elements into voice agents enhances users' perception of anthropomorphism. This finding confirms the robustness of our experimental design in effectively exploring UXs across different levels of anthropomorphism. Interestingly, this study found no significant differences in trust and perceived safety between Agents A, B, and C. This could be attributed to the inherent complexity of these constructs, which may not be influenced solely by the human-like qualities of the voice agents. Trust and perceived safety are multifaceted and could be influenced by prior experience with technology, individual differences in risk perception, and the specific context of use. For instance, one participant commented, \"While the human voice lacked unnecessary emotional explanations, it felt more trustworthy and efficient\" (Agent B, sixth participant). Conversely, another noted, \"As the voice felt more familiar, the trust and safety perception diminished, especially since it used a human voice\" (Agent C, seventh participant). In contrast, positive feedback included, \"The explanations provided a sense of stability, and the empathetic remarks made me feel the agent considered my safety and comfort\" ([PERSON] C, 22 nd participant). These varied responses highlight the need for further research to dissect these constructs and identify other factors that may influence users' trust and perceived safety when interacting with voice agents in autonomous vehicles. It also suggests that while humanized voices may increase perceived anthropomorphism, this may not necessarily translate into increased trust or perceived safety. Thus, additional research is required to dissect these constructs and identify other factors that may influence users' trust and perceived safety when interacting with voice agents in autonomous vehicles. The results regarding intention to use revealed several interesting patterns. Specifically, Agent A showed a higher intention to use than Agent B, and Agent C showed a higher intention to use than Agent B, with no significant difference between Agents A and C. This suggests that while humanized speech and a human voice contribute positively to intention to use, the mechanical voice of Agent A still has a strong appeal. One possible explanation is that users may perceive the mechanical voice as more efficient or reliable, qualities that are highly valued in utilitarian contexts such as driving [55]. In this regard, mechanical voices could play a significant role in future systems, particularly in contexts where efficiency and reliability are prioritized over emotional engagement, such as automated customer service, navigation systems, or industrial environments. Additionally, individuals who prefer functional interactions or are less inclined toward emotionally driven interfaces may find mechanical voices more appealing. This suggests that the value of mechanical voices may continue to be recognized in certain fields and for specific user preferences, and that the adoption of mechanical voices could remain relevant in applications in which trust, accuracy, and task-oriented communication are important. Additionally, the use of a human voice without a humanized speech strategy for the anthropomorphic design of Agent B may have caused participants to feel that the conversational communication was different from what they would expect in either a normal human-to-human conversation or a human-to-voice agent conversation.