One of the main hubs for United Airlines is located at George Bush Intercontinental Airport (IAH) in Houston, specifically in Terminals B, C, and E. United Airlines IAH Terminal operates its regional flights out of Terminal B, and United handles its domestic and international flights out of Terminals C and E. Because of its widespread presence, United is able to provide a variety of flights, making IAH one of the airline's busiest airports nationwide. Because the terminals are connected, travelers may move between gates with ease thanks to the Skyway, an efficient subterranean train system that shuttles people between the terminals.