What does it mean that the Yangtze River Bridge runs north and south, and three roads lead to the snowy area?

A bridge connecting the north and south of the Yangtze River refers to the Nanjing Yangtze River Bridge. At that time, the opening of Nanjing Yangtze River Bridge made the traffic between the north and the south of the Yangtze River smooth and played an extremely important role in the economic development of the Yangtze River Delta region. Three steps into the snowy area, Happy Sino-Tibetan refers to the Qinghai-Tibet, Xinzang and Kangzang highways designed and built by China in 1950s. Starting from Xining in Qinghai, Yecheng in Xinjiang and Xikang in Sichuan (now called Ya 'an), they are connected with Tibet. They were the traffic lifeline connecting Tibet when there was no railway connection at that time, and also the core route of Tibet's foreign exchange.