Concourse B (which has 28 gates) composes the western half of the building. It is the first of the permanent elevated midfield concourses. Originally constructed in 1998 and designed by Skidmore, Owings & Merrill and Hellmuth, Obata and Kassabaum, the B concourse contained 20 gates. In 2003, 4 additional gates were added to concourse B, followed by a 15-gate expansion in 2008. In addition to the AeroTrain station located between gates B51 and B62, Concourse B also has an underground walkway to connect it to the main terminal. Concourse B is used by some international carriers, and is also utilized by all non-United domestic and Canada flights. The facility also includes a British Airways Galleries lounge, a Lufthansa lounge divided into Senator and Business class sections located between gates B49 and B51, and a Turkish Airlines Lounge near gate B43.