As Autonomous Vehicles (AVs) remove the human driver from road interactions, external Human-Machine Interfaces (eHMIs) become essential for communicating with human road users (HRUs). This dissertation investigates how cultural differences and branding affect eHMI design, understanding, and effectiveness.

Through cross-cultural studies in China, Germany, and the U.S., it identifies universal preferences (e.g., for displays) alongside culture-specific expectations and responses. Findings support a modular, multi-modal eHMI system that combines a universal hardware base with culturally adaptive software to tailor message content and delivery. Symbol-based visuals and egocentric perspectives enhance clarity, while light, context-sensitive branding may be acceptable in non-critical scenarios. This research offers a scalable, culturally aware framework for AV communication that enhances safety, trust, and global usability.