Core Viewpoint - The development of the second high-speed rail lines in major cities like Shenzhen, Beijing, and Chengdu is essential to meet the increasing passenger demand and upgrade existing rail technology [1][10][12]. Group 1: High-Speed Rail Expansion - Shenzhen's Development and Reform Commission has initiated the planning for the second high-speed rail line extending to Hong Kong [1]. - The second high-speed rail lines are under construction in major corridors, including Beijing-Shanghai and Chengdu-Chongqing [2]. - Major cities are entering the "second high-speed rail" era, enhancing the existing "eight vertical and eight horizontal" high-speed rail network [3]. Group 2: Capacity and Demand - The existing high-speed rail lines are experiencing capacity constraints, with peak periods leading to ticket shortages [7][10]. - The Beijing-Shanghai high-speed rail, which operates the most trains globally, still faces demand exceeding supply during peak times [10]. - The need for a second high-speed rail line is driven by the increasing passenger flow and the necessity for technological upgrades to achieve speeds of 400 km/h [10][12]. Group 3: Geographic Coverage and Connectivity - The second high-speed rail lines aim to connect more regions, addressing gaps left by the first high-speed rail lines [12][14]. - The planned Guangzhou-Shenzhen second high-speed rail will connect major airports and extend to Hong Kong, enhancing regional connectivity [14][16]. - The Chengdu-Chongqing line will significantly reduce travel time between the two cities, improving access to central Sichuan [18]. Group 4: Economic and Strategic Considerations - The overall high-speed rail network in China has reached 81.5% completion, with 48,000 kilometers of operational lines, covering 97% of cities with populations over 500,000 [22]. - Future high-speed rail construction will prioritize economic viability, population density, and strategic importance, moving away from indiscriminate expansion [22][23]. - Only a few high-speed rail lines, such as Beijing-Shanghai and Beijing-Tianjin, have achieved sustained profitability, indicating a shift towards more economically sound projects [23].