With continued motorization and urbanization in Chinese cities, there is a growing demand for innovative transportation policies to address the challenges of congestion, local air pollution, and greenhouse gas emissions. Using Beijing and Shanghai as case studies, this paper draws on in-depth interviews with municipal government officials and non-governmental experts to document the ways in which transportation policy is currently implemented at the city-level in China. Using recursive and iterative qualitative data analysis techniques, this study (1) further justifies existing factors that contribute to transportation policy decisions, (2) identifies other factors that contribute to or obstruct effective transportation policy implementation in the two cities. The results indicate policy learning, public opinion, and data informatization emerge as key contributors to policy implementation; while public complaint, unilateral decision-making, inadequate coordination among relevant departments, and failure to commit to adaptive policy implementation practice pose significant challenges to adopting timely and appropriate transportation policies. This study finds that in Beijing, and even more so in Shanghai, public opinion is both a contributor and an obstacle to the introduction of new transportation policies. The motivation for policy comes partly from public opinion, but it is also public complaint that sometimes stops policy implementation. The authors conclude by describing the transportation policymaking process in Beijing and Shanghai and identifying where contributors and obstacles fit within this process.