Note:
(a) "In 1912, shortly after he took over as China's first president, Sun Yat-sen called for a trans-Tibetan line, not least to help prevent Tibet from falling under the sway of Britain (which had already invaded Tibet from India a decade earlier [1904])."
(i) In the Web, "trans-Tibetan" rail is not associated with Sun, but used occasionally (and decidedly unofficially) to describe the recent railroad that China completed in 2006.
(ii) 张双志, 孙中山设计的西藏发展蓝图. 中国民族报, May 17, 2009.
dangshi.people.com.cn/GB/85038/9313650.html
"孙中山在《实业计划》[1920; English: The International Development of China] 中提出拟在全国修建 * * * 铁路系统。修建通达西藏地区的铁路线主要是在高原铁路系统中，包括：拉萨—兰州线，拉萨—成都线，拉萨—大理车里线，拉萨—提郎宗线，拉萨—亚东线，拉萨—来吉雅令及其支线，拉萨—诺和线，拉萨—于阗线。
(A) The "dangshi" in the URL is 党史.
(B) Economist is correct in the singular form of Trans-Tibetan Line, for Sun proposed one in 1912. Then in his 1920 book he proposed numerous ones (I am unsure whether it was just his imagination).
(b) "But it is only after building the world's second-longest railway network—including, in the past few years, by far the biggest high-speed one—that China’s government has felt ready to take on the challenge."
list of countries by rail transport network size https://en.wikipedia.org/wiki/Li ... nsport_network_size
(top 5: US> China> Russia > India > Canada)
(c) "That [2006] line, connecting Lhasa with Golmud in Qinghai province to the north (and extended two years ago from Lhasa to Tibet's second city, Shigatse)"
Golmud 格尔木市 https://en.wikipedia.org/wiki/Golmud
(The name of the city derives from Mongolian, and its literal meaning in the local Western Mongolian is "Rivers")
(d) "In Litang 理塘县, a town high up in Sichuan on that difficult stretch" of the new line
(e) "The journey time from Chengdu to Lhasa is a gruelling three days by road, or more than 40 hours by train through Qinghai [including the 2006 stretch]. The new line will reduce it to a mere 15 hours."
(f) "A Chinese government website, China Tibet News 中国西藏新闻网, said in 2014 that building the Sichuan-Tibet railway 川藏铁路 had become 'extremely urgent,' not just for developing Tibet but also to meet 'the needs of national-defence-building.' "
(g) "a railway-building spree * * * On May 16th Tibet Daily 西藏日报 * * * said that work would start in the coming five years on around 2,000km of track. It would include a line from Shigatse to Yadong 亚东县 (or Dromo), near the border with India and Bhutan, and another one to Jilong (or Gyirong 吉隆县 ['Its name in Tibetan, Dzongka means "mud walls" '; en.wikipedia.org), near the border with Nepal."