Demand and supply principle predict public transport tool passenger behaviourEconomists need to use the right economic ideas to predict consumer behaviour. So, Misuse the wrong economy ideas to predict consumer behaviours. It will do more wrong judgement to evaluate or predict why and how and when the country's consumer behaviours will change. It is every economist needs to consider issue. For example, the economy idea application of economic supply-demand principles to public transport. Different fares would give commuters with more-flexible hours the incentive to avoid peak travel times. They would allow passenger traffic to spread out over time, reducing the pressure on the public transport system when enabling even larger total passenger flow. IT aims to reduce traffic congestion, increased public-transport use, reduced car-bon emissions and cause air pollution and generated considerable revenue for the country's transport system. So, if the country can apply supply and demand economic principle to attempt to predict how many passengers number needs to catch transport tools to go to work or go to school or other activities. Then, it can predict how many bus, ferry, taxi, train, underground train, tram etc. different public transport tools to satisfy future public transport passengers' needs in society. So, this demand and supply principle is the comparative best rule to predict any kinds of public transport passengers' road needs, when they need to either go to school, go to office, go to leisure or shopping etc. different kinds of activities. So, applying the demand and supply principle to predict road and sea public transport passengers can help the country to reduce air pollution when they feel that they can find any public transport tools to catch any time conveniently, then it can encourage them to reduce car purchase desire. When many people choose to catch public transport tools, then it will reduce many cars number on the road. Then, air pollution will reduce as well as any public transport tools' income will also increase as well as traffic jam will also reduce.