This paper focus on the introduction of Autonomous Vehicles (AVs) in cities of varying densities. While existing research focuses on the technology itself or government regulation, I seek to understand how urban density influences the way AVs are introduced and the changes they potentially bring. I develop a framework that links policy instruments, technology application, and urban density. Cases from China and the United States were studied. The results suggest that while population density does matter, political institutions and governance styles often play a greater role. By comparing cities such as Beijing, Suzhou, San Francisco, and Phoenix, this study highlights the need for AV policies that balance spatial and institutional considerations.