Adaptive cruise control (ACC) is becoming increasingly common; however, many users still struggle to understand system states and interventions, which may hinder trust and acceptance. Prior research has focused primarily on visual human–machine interfaces (HMIs), but driving is a visually demanding task. Therefore, voice-based HMIs are increasingly being considered as an alternative or complementary modality; however, empirical evidence regarding their acceptability for ACC remains limited, particularly in partially automated systems that require continuous driver monitoring. This study examines the subjective a priori acceptance of voice-based ACC notification designs through a video-based experiment. Participants (N = 240) view standardized highway driving scenarios and evaluate multiple HMI conditions that vary in informational and cautionary audio–visual content relative to a silent baseline providing purely visual content. The results reveal significant differences in acceptance across notification conditions. Overall, simple notification strategies exhibit consistently moderate acceptance, without eliciting strong rejection, whereas more detailed or strongly directive voice messages tend to be evaluated less favorably. Furthermore, the exploratory analysis yields preliminary, hypothesis-generating insights into age-related patterns in user evaluations. Overall, our findings suggest that the design of voice notifications may be an important factor in shaping the a priori acceptance of ACC and emphasize the need for further research targeting diverse user groups.