This chapter first explains that road congestion can be seen as a market failure problem caused by "external costs"; secondly, it compares the results of free market equilibrium and economic optimal equilibrium of road use; thirdly, it discusses how to achieve economic optimal equilibrium through congestion pricing policy, and then compares the efficiency of price policy and non price policy; finally, it explains why the economy is in an economic state Optimal policies are often difficult to implement in a democratic society.