Tianjin Metro or Tianjin Rail Transit is the rapid transit system in the city of Tianjin, which was the second city, after Beijing, in mainland China to operate a subway system. Opened in 1984, the system has 6 operating lines and 185 stations spanning 220 km (137 mi). The lines are jointly operated by two companies, namely the Tianjin Metro Group Co. Ltd and the Binhai Mass Transit Development Co. Ltd. The former operates Lines 1, 2, 3 and 6, while the latter operates Line 5 and Line 9. The two companies merged and regrouped as the Tianjin Rail Transit Group Co. (TRT) in 2017.