Design knowledge plays a key role in the design of a good automotive user interface. In this paper, we propose a qualitative field study and design approach to develop a design knowledge system for automotive user interface. The methods used are based on contextual design and similar concepts from the area of User Centered Design (UCD). Using the data from field study and design as the knowledge content, we developed a web-based design knowledge system: Transportation User Interface Design Knowledge System (TUI) that consists of user, design, and scenario modules. Designers and engineers can use the system to identify drivers' needs, generate design ideas, and help them enhance the automotive user interface. The system has been adopted in one automotive design firm in China, and one actual interface has been designed with the help of the system. The success of the adoption of the system is also discussed in this paper.