On US Sept 11 Terrorist Attack to public transportation tools influence aspect, in Washington and New York cities, although subway and bus trips significantly outnumber for hire vehicle trips, for hire vehicles provide some services that the mass transit system can't. Many Washington and New York cities residents use for hire vehicles when subway or bus lines are too far away from their homes or destination or when mass transit is perceived as too slow or requires too long a wait. IN addition to convenience and speed, passengers may also select for hire vehicles for comfort, privacy and the relative ease of transporting bulk items and packages. Moreover, most Washington and New York residents get around using subways or buses. Public transit makes up the largest part of Washington, New York city transportation system by ridership, but taxi service has significant role. SO, although air pollution will influence bus, ferry, underground train, tram public transportation tools needs much. Due to they choose to sell their private vehicles or they choose to walk to avoid often driving cars to influence Washington, New York cities air to be more polluted, but the taxi need is not needed vey much, they won't prefer to choose taxi transportation tool to catch. It is possible due to taxi fee is charged higher than other general public transportation tools in Washington, New York cities US. So, Washington and New York cities air pollution won't influence taxi service need to increased significantly.In the future, Washington and New York residents will continue to consider air pollution challenge. So, the Washington and New York cities public transportation service will trend to have the lowest rate of private car ownership in the nation, instead of New York, Washington cities and the highest utilization of for -hire services. Every day Washington, New York residents and tourists take trips in-for-hire vehicles, relying on them to get to work, school, medical appointments to and from the airports and other destinations. Hence, future New York and Washington cities residents will depend on public transport tools or vehicle rent services more than to drive themselves owning vehicles to go to anywhere often, when they begin to consider air pollution challenge in their both large cities US.It seems that these both big cities, US public transportation tools and vehicle rent service needs will be increased . Even, future these both big cities' transportation tools and vehicle rent service price will be raised, their higher price won't influence these both cities residents to choose to catch them to go to anywhere because they will consider future air pollution serious challenge will be increased from their frequent driving behavioral cause.