Tokyo is an important center of traffic. Tokyo has a big railroad and two airports, the international airport Narita and the national airport Haneda. The city also has a large subway. There are also four harbors in Tokyo, the biggest is Yokohama. Tokyo had the first public monorail. Tokyo has almost no pollution problems. The cars are all supplied with instruments that make the pollution as less as can be. The public transport is also well organized by many private corporations. Private corporations also collect the trash in the city.