The Port Authority of New York and New Jersey bridges the sometimes troubled waters between the two states and helps with many of the region's other transportation needs. The bi-state agency operates and maintains airports, tunnels, bridges, a commuter rail system, shipping terminals, and other facilities within the 1,500-sq.-mi. Port District surrounding New York Harbor, including the World Trade Center site in Lower Manhattan. A self-supporting public agency, the Port Authority receives no state or local tax money. It relies on tolls, fees, and rents. Airport operations account for the majority of its revenue. The two governors each appoint six of the 12 members of the agency's board and review its decisions.