Bangkok Mass Transit System (BTS) or Skytrain (Thai: รถไฟฟ้า) is the elevated metro system in Bangkok, Thailand, operated by Bangkok Mass Transit System Public Company Limited (BTSC) under a concession granted by the Bangkok Metropolitan Administration (BMA). The Skytrain with 23 stations along 2 lines, was opened on December 5, 1999 by HRH Princess Maha Chakri Sirindhorn. The Sukhumvit line runs northwards and eastwards, terminating at Mo Chit and On Nut respectively; the Silom line plies Silom and Sathon, the Central Business District of Bangkok, terminating at the National Stadium and the Taksin Bridge. The lines interchange at Siam station and have a combined route distance of 23 km. The Skytrain is formally known as the Elevated Train in Commemoration of HM the King's 6th Cycle Birthday (รถไฟฟ้าเฉลิมพระเกียรติ 6 รอบ พระชนมพรรษา) because it was opened to the public on HM King Bhumibol Adulyadej's 72nd birthday.