This study analyzed the greenhouse gas (GHG) reduction potential and cost of urban road transportation policies from a boarder perspective including tank-to-wheel (TTW) and well-to-wheel (WTW) assessments, with Chongqing in China taken as the case city. Three policies and two mixed policies, including improving the fuel economy of passenger cars, promoting electric vehicles (EVs), and promoting natural gas vehicles (NGVs), are analyzed in this study. The two groups of mixed policies are developed to analyze the interaction between the policies. The results indicate that all the policies will reduce TTW and WTW fuel consumption and GHG emissions from 2016 to 2035. During this period, promoting an NGV policy will have the smallest marginal abatement cost (MAC) but the smallest GHG reduction potential, and promoting an EV policy will have the largest MAC but the largest GHG reduction potential from TTW. However, considering the GHG emissions from upstream energy consumption, the GHG emission reduction from promoting the EV policy is reduced and that of improving the fuel economy via the motor vehicle policy will increase significantly, resulting in a larger MAC from WTW than from TTW. With the mixed policies, hedging effects impact fuel savings, GHG emission reductions, and MACs. We put forward some policy suggestions to provide a reference for the formulation and adjustment of China's urban road transportation policies to cost-effectively mitigate GHG emissions in the future.