We examine the connection between public knowledge and attitudes in the context of urban transportation policies. We categorize policy knowledge into received, subjective, and reasoned knowledge, and measure them empirically using a survey of Shanghai’s residents (n=1,000) on the vehicle license auction policy. We quantify the relationship between the three types of knowledge and public acceptance and its predecessors (perceived effectiveness, affordability, and equity). We find variegated impacts of knowledge on acceptance: reasoned knowledge increases acceptance but subjective knowledge decreases it, while received knowledge has no direct impact. Public information needs to emphasize societal benefits and the underlying policy rationale.