Research purposes: With the further implementation of the Medium and Long-term Railway Network Plan and the progress of investment and financing system reform, some railways in difficult mountain areas not serving as network trunks and functioning not so important are increasingly put on the agenda. The construction scale of projects often becomes the focus to decide to construct a single-track line, a double-track line, or a single-track line with conditions reserved for future track doubling. So, this paper focuses on those railway projects which must be doubled in the far future (bridges and tunnels accounts for 70% or more), compares and studies the scheme of single-track line, and the scheme of single-track line with conditions reserved for future track doubling, thus proposes suggestions on how to decide the construction scale for difficult mountain railways.
Research conclusions: (1) The construction scale of railways project in difficult mountainous areas should take the forecast of traffic volume and the local economic development into consideration. (2) Future track doubling is difficult for mountain railways with 50% or higher bridges & tunnels ratio, and also requires high investment, which is unfavorable for land requisition, demolition and removal, environmental protection and land conservation. (3) In the difficult mountainous areas where double-track line is needed to meet the transportation demand in the long run, it is suggested to construct a double-track line once upon a time through friendly consultation, in line with the principle of scientific demonstration and moderate advance, so as to achieve the best comprehensive benefits. (4) The research results can provide a reference for railway survey and design.