Abstract .Transportations one of the important indexes of air pollution in cities has always occurred in the form of a big Unavoidable problem. Lack of comprehensive approach and enough (Sufficient) attention toward transportation and traffic issues have unsparing social, economical and environmental costs and damages in the country which the most important of them are: high fuel consumption and growth of the fatal and injury crashes, air pollution and environmental damages. Among the public transportation networks, railway public transit is known as the healthiest, fastest, safest and generally the most efficient transportation network which is proved the undeniable role in solving economic, social and environmental problems caused by public transport and traffic problems. Considering the political and economic centrality of Tehran as capital of Islamic Republic of Iran with an increasing population of over 10 million people, and the construction of satellite cities, and conducting population to these cities, it is important to construct several connecting subway lines for these satellite cities. This paper focuses on economic problems via comparing underground subway as public vehicle with motor vehicle.