According to the development of self-driving technologies are rapidly progressing, self-driving taxis are expected to be commercialized and narrow the social and economic isolation of people with disabilities as a means of personal transportation. However, there is a lack of interest and research on increasing informatical and physical accessibility so that self-driving taxis can widely use as transportation for people with disabilities. This paper presents eight universal access principles (four principles each in two layers: digital and physical) and detailed examples describing the principles. Eight principles build through (1) existing literature studies mainly based on the prominent universal design principles of NC State University, and (2) robot-taxi journey analysis of users with three types of disabilities (wheelchair users, blindness, and limblessness). Moreover, I have repeatedly verified and co-design examples of the eight principles through interviews with people with disabilities. This thesis facilitates discussion of how much universal accessibility of self-driving cars is necessary and essential and leads to more research and design.