Classify vehicles within a country is possible but in the world would not be practical.那就按国内的来。。。随便分一分就好了。。关键是看句式To reduce the air pollution from vehicle emission and also to contol the noise pollution from the growing vehiecle population , it is good to classify the vehicles. The classification can be in term of types and the capacity of the engines (CC). Classify by type of vehicle will help in the curb in noise pollution and charge the tax accordingly. We should also consider that if the vehicle, like public bus is a public transport means, the tax should be lower and the population can be increase base on the needs. Private car on the other hand is for individual need, so the tax can be higher to curb people from owning it. Classification by the car capacity will save the country oil consumption and air pollution. Higher capacity car must be taxx higher for the annual fee. If you want to drive big car, you have to pay more annual tax.