Beijing, as the capital and one of the four municipalities of the People's Republic of China (PRC), is a transport hub, with a sophisticated network of roads, railways and two major airports. Five completed ring roads encircle the city with nine expressways heading in virtually all compass directions, supplemented by eleven China National Highways. Transport in the capital is overseen by the Beijing Municipal Commission of Transport. Road network Ring roads The city is served by five completed ring roads. From the centre of the city outward, they are: 2nd Ring Road 3rd Ring Road 4th Ring Road 5th Ring Road 6th Ring Road The "1st Ring" of Beijing refers to the historic tram route (now demolished) through Xidan, Ping'anli, Di'anmen, Beixinqiao, Dongdan and Tiananmen. No ring roads are built on this route but it is still called "1st Ring". From that on, ring road built on Beijing's historic city limit is called 2nd Ring. Expressways Main topic: Expressways of Beijing Nine toll expressways link Beijing to its suburbs, outlying regions, and other cities; these are: Jingzang Expressway (Madian Bridge to Badaling and Yanqing District) Jingcheng Expressway (Connects Beijing to Chengde in Hebei province) Airport Expressway (Sanyuanqiao to Beijing Capital International Airport) Jingtong Expressway (Dawang Bridge – Tongzhou District) Jingha Expressway (Beiguan Roundabout – Yanjiao in Hebei province) Jingshen Expressway (Sifang Bridge – Shenyang) Jinghu Expressway (Runs from Beijing to Shanghai) Jingkai Expressway (Yuquanying–Yufa) Jingshi Expressway (Liuliqiao–Shijiazhuang) China National Highways Eleven China National Highway routes depart from Beijing in virtually all compass directions: China National Highway 101 (Dongzhimen–Chengde–Shenyang) China National Highway 102 (Chaoyangmen–Harbin) China National Highway 103 (Fenzhongsi–Tianjin–Tanggu) China National Highway 104 (Yongdingmen–Fuzhou) China National Highway 105 (Yongdingmen–Zhuhai–Macau) China National Highway 106 (Yuquanying–Guangzhou) China National Highway 107 (Guang'anmen–Shenzhen) China National Highway 108 (Fuxingmen–Kunming) China National Highway 109 (Fuchengmen–Lhasa) China National Highway 110 (Deshengmen–Yinchuan) China National Highway 111 (Dongzhimen–Heilongjiang province) Traffic congestion Beijing as of 2011 has an estimated 5 million registered cars on its roads, so traffic congestion is widespread. Traffic in the city centre is often gridlocked and is only predicted to get worse as the number of vehicles on Beijing's roads increase. It is predicted by 2016 Beijing will have over 6 million cars on its roads. To combat congestion the local government has rapidly been building the subway system adding more lines and working towards doubling the length of the subway system by 2015. In addition to