With continued motorization and urbanization in Chinese cities, there is a growing demand for innovative transportation policies at the city level to address the challenges of congestion, local air pollution, and greenhouse gas emissions. Using Beijing and Shanghai as case studies, this paper draws on 32 in-depth semi-structured interviews with municipal government officials, academics, and transportation professionals to explore the city-level transportation policymaking process in Chinese megacities. Across the two cities, we identify three common contributors – policy learning, data informatization, and public opinion—and four obstacles—public complaint, unilateral decision-making, inadequate coordination among relevant departments, and lack of adaptiveness in policy implementation practice—to adopting timely and appropriate transportation policies. We then introduce a processual model that connects the contributors and obstacles identified within the flow of transportation policy among key actors in city-level government. This process shows how transportation policymaking in Chinese megacities is often reactive to public outcry over a transportation problem. This problem is investigated by a technical government research center that reports to the municipal transport committee. This committee then assesses public opinion and submits a policy recommendation to city government leadership, who make the final policy decision. Based on both case studies, we discuss potential recommendations for how to better enable transportation policymaking at the city level in China through more formalized processes of policy experimentation and public participation. We conclude with a discussion of limitations and areas of future research.