⦁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. When the country can evaluate how many people choose to catch bus or taxi or ferry or train or underground train, or tram or train etc. different kinds of public transport tools, then the country can predict the more accurate public transport tools number to every kind of public transport tool to satisfy their journey needs. e.g. whether underground train or train or tram need to decrease or increase the frequent times or number to catch the volume of passenger in busy or non-busy time; or whether bus company has need to increase how much buses to catch the city location passengers when they are living in the city. Moreover, supply and demand principle can help any public transport tools to explain why their passengers number reduces in the year, it may due to fare charge is unreasonable, feeling uncomfortable to sit on the seat or air condition is poor in the transport tool environment, or there are no more seats because many there are much time is full passenger and no seat vacancy to provide to them to sit . So, supply and demand principle can help any kinds of public transport tools to find whether which is (are) the factor(S) can influence the current or last year passengers number reduce. Then, they can concentrate on improving their weaknesses to raise their service quality . So, supply and demand principle can also help they to evaluate whether what their weakness are in order to improve to increase passengers number. They can do questionnaires to enquiry their passengers' response to evaluate whether which areas of services that they feel unsatisfactory.