User-Centered Design with AI in the Loop: A Case Study of Rapid User Interface Prototyping with "Vibe Coding"

We present a case study of using generative user interfaces, or ``vibe coding,'' a method leveraging large language models (LLMs) for generating code via natural language prompts, to support rapid prototyping in user-centered design (UCD). Extending traditional UCD practices, we propose an AI-in-the-loop ideate-prototyping process. We share insights from an empirical experience integrating this process to develop an interactive data analytics interface for highway traffic engineers to effectively retrieve and analyze historical traffic data. With generative UIs, the team was able to elicit rich user feedback and test multiple alternative design ideas from user evaluation interviews and real-time collaborative sessions with domain experts. We discuss the advantages and pitfalls of vibe coding for bridging the gaps between design expertise and domain-specific expertise.